spontaneous neoplasms in amphibia: a review and ... · mor, situated on the head, invaded the skin...

Spontaneous Neoplasms in Amphibia: A Review andDescriptions of Six New Cases*

MICHAELBALLS

(Station de Zoologie expÃ©rimentale,Route de Malagnou 154, Geneva, Switzerland)

SUMMARYFifty-two previous accounts of neoplastic growths in Amphibia are listed and sum

marized. Six new cases, including five of lymphosarcoma, are described. The diversity,sites, and distribution of amphibian tumors are discussed.

The last detailed review of neoplasms occurringspontaneously in amphibia was that of Schlum-berger and LÃ¼cke(38), who summarized sevencases in Urodeles and 22 in Anurans. The sameauthors (22) also discussed the literature on theexperimental induction of tumors in these coldblooded vertebrates, as did Leone (18). Schlum-berger and LÃ¼ckeconsidered that, in spite of thesmall number of tumors, there was no good reasonfor believing amphibians to be less susceptible toneoplastic growth than fish or other vertebrates.This view has been upheld by the increase in ourknowledge of amphibian tumors as a result ofrecent research.

A completely comprehensive review is madedifficult by both the isolated occurrence of animalswith neoplastic disease and the varied journals inwhich the details are published. Lists of cases havemore recently been given by Leone (18) and Stolk(49). Schlumberger (37) and Reichenbach-Klinke(33) both comment on the high incidence of cutaneous tumors in the cases reported and the lackof visceral neoplasia. The author considers thatthis position has been so altered by the work ofInoue (16, 17), Mori (24), Schlumberger (37), El-kan (10), and the occurrence of the six new casesto be described below that there is a fresh opportunity to discuss the distribution of spontaneous tumors in the Amphibia.

The known reports of spontaneous neoplasms* This investigation has been carried out in the Embryology

Laboratory, Department of Zoology, Oxford University, andat the Institut de Zoologie, Geneva University. The workhas been supported by grants from the Medical Research Council (U.K.) and the Fonds National Suisse pour la RechercheScientifique.

Received for publication May 29, 1962.

in amphibians are listed chronologically in Table1. Short abstracts of those original publicationsnot summarized by Schlumberger and LÃ¼cke(38)follow.

ABSTRACTS OF REPORTS OF TUMORSIN AMPHIBIA

TUMORSIN ANUBALlambÃ©sand Garcia (20) : described the spontaneous appear

ance of multiple tumors on the left leg, the abdomen, and between the eyes of a frog (Rana catesbiana). The tumors werediagnosed as adenoepitheliomas of skin. A tumor fragmentgrew rapidly after transference to the anterior eye chamber ofanother frog.

Stolk (48) : found a spherical encapsulated tumor of kidneyin Bufo bufo.

Rose (85): transplanted fragments of a fat-body tumor ofa Rana pipiens. The original tumor had invaded one lung andretained the ability to store oil. The transplants took in allcases, but oil storage was not a property of further seriallytransplanted fragments.

Rostand (36) : found a female Rana temporaria bearing inthe anal region a melanic tumor covered with rounded protuberances.

Stolk has investigated a number of tumors in Anura :(a) (49). An adenoma of parotid gland in Bufo marinus.

This was a white, nodular structure composed of cystic andnoncystic tissue. No infiltration, metastasis, or parasites werefound. The tumor cells had large, vesicular, and polymorphicnuclei, some being acidophilic and having cytoplasmic inclusions.

(6) (50). Multiple adenoma of skin in fiana artalis. Thenodules consisted of stratified squamous epithelium cells arranged as tubules, acini, or solid sheets separated by a delicatestroma. The nuclei were large, vesicular, and polymorphic, andthe cytoplasm contained some special inclusions. There was noinfiltration or metastasis, and the tumor was apparently benign.

(c) (51). Hemangioma of heart in Hyla arborea. A dark-redmass was found on the side of the ventriculus, being composedof a network of dilated blood vessels separated by a stroma.Proliferation of the endothelial cells had proceeded to such anextent that some blood vessels were occluded.

(d) (54). Erythrophoroma of skin in Dendrobatestypographi-

1142

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TABLE 1

REPORTSOFSPONTANEOUSNEOPLASMSIN AMPHIBIA

DATE1868189819021905190619081912191219181914191919281928192919301932193419341934194819481948194919501952195719571958195819591959195919601960196019601961New

c196219621962196219621962AUTHORSSPECIESTUMORSITENo.

ANIMALSAnuraEberth,

C.J.Ohlmacher,H.P.Vaillant,

L., & Pettit,A.Smallwood,W.M.Plehn,

M.Murray,J.A.Pavlovsky,

E.N.Pavlovsky,E.N.Carl,

W.Pentimalli,

F.Secher,K.Masson,

P., &Schwarz,E.Volterra,

M.Duany,J.Gheorghiu,,

I.[6)Downs,A.W.Pirlot,

J., & Welsch,M.Pirlot,J., & Welsch,M.LÃ¼cke,B. [32,47]Schlumberger,

H.,&LÃ¼cke,B.Schlumberger,

H.,&LÃ¼cke,B.Willis,

R.A.LlambÃ©s,J. J., &Garcia,J.

M.Stolk,A.Rose,

S.M.Stolk,A.Stolk,A.Rostand,J.Stolk,A.Stolk,A.Stolk,

A.Stolk,

A.Elkan,E.Elkan,E.Elkan,E.Elkan,E.Stolk,

A.asesBalls,

M.utÃuu((Rana

sp.RanavirescensRanaesculentaRanapipiensRanaesculentaRanasp.Ranasp.Ranasp.RanaesculenteRana

sp.RanaesculentaRanaesculentaCeratophrus

ornataRanacatesbÃ¬anaRanaesculentaRanapipiensRanafuscaRanafuscaRanapipiensRanacatesbianaRana

clamitans(tadpole)Rana

esculentaRanacatesbianaBufo

bufoRanapipiensRufomarinusRanaarvalisRanatemporariaHuÃaarboreaDendrobatestypo-graphicusHuÃa

arboreameri-dionalisIlyla

arboreaRufocalamitaXenopuslaevisXenopuslaevisXenopuslaevisBufo

bufojapÃ³nicasXenopus

laevis laevisXenopus

laevisvic-torianus/'Xeno-pus

laevislaevisXenopusfraseriXenopusfraseriXenopus

laevis laevisXenopus

laevislae-oaAdenomaOsteogenic

sarcomaFibromaAdenocarcinomaCarcinomaAdenocarcinomaAdenomaAdenocareinomaHypernephroma(

=carcinoma)AdenomaAdenomaAdenocarcinomaFibrosarcomaAdenocarcinomaSarcomaAdenocarcinomaAdenomaMyxofibrochondromaAdenocarcinomaNeurosarcomaMyxosarcomaHepatomaAdenoepitheliomaCapsulated

tumorCarcinomaAdenomaAdenomaMelanomaHaemangiomaErythrophoromaGuanophoromaXanthoplioromaAdenocarcinomaAdenocarcinomaFibromaFibromataFibromaLipomaLymphosarcomaLymphosarcomaLymphosarcomaLymphosarcomaLymphosarcoma

& leukemiaSkinFemurBuccal

cavityKidneyOvarySkinSkinSkinKidneySkinSkinSkinLeg,

liverSkinLegKidneySkinLegKidneySacral

plexusTailLiverSkinKidneyFat-body,

lungParotidglandSkinSkinHeartViscera

&skinSkinSkinLungKidneyPelvisFaceSkinUnder

skinVisceraVisceraVisceraHead

muscle & visceraHead

muscle, viscera & blood1111112111111111171<6.7%111111111111111118111111



1144 Cancer Research Vol. 22, November 1962

TABLE 1â€”Continued

DATE190219031908191619201923193519471948195019531954195419581958AUTHORSSPECIESTDUOBSITENo.

.\sni\L3UrodelaVaillant,

L., & Pettit,A.Pick,

L., & Poll,H.Murray,

J.A.Krontovsky,A. A.[12JTeutschlaender,

O.Schwarz,E.Champy,

C., &Champy,C.Broz,

O.Sheremetieva-Brunst,E.,&

Brunst,V.Rickenbacher,J.Sheremetieva-Brunst,E.Inoue,S.Mori,

H.Stolk,

A.Schlumberger,H. G.MegalobatrachusmaximusMegalobatrachusmaximusTrituras

cristatusSiredonmexicanumSiredonmexicanumMegalobatrachusmaximusTriturus

alpestriÂ»Triturus

teaniatusSiredonmexicanumTriturus

alpestriÂ»SiredonmexicanumTrituruspyrrhogas-terTriturus

pyrrhogas-terTriturus

taeniatusNecturusmaculatitiFibromaCarcinomaAdenocarcinomaMelanomaMelanosarcomaFibromaCarcinomaChondromaMelanomaCarcinomaEpitheliomaLymphosarcomaSarcomaFibromaAdenocarcinomaPalm

offootTestisSkin-glandsSkinSkinUnder

skinSkinSkinSkinSkinSkinVisceraLiverSkinKidney1111113121112251

cus. The animal had a red, irregular mass on the trunk andred nodules on the liver, spleen, and kidneys. These consistedof fusiform cells containing small pigment granules and withvacuolar cytoplasm. An erythrophoroma is a tumor arisingfrom the red pigment-containing erythrophores.

(e) (55). Guanophoroma of skin in Hyla arboreameridionalis.This tumor was found between the eye and tympanic membrane and, when sectioned, had a silver-white sheen. Microscopically, it was made up of spindle-shaped cells containingguanin crystals. Vascularization was scanty, and necrosis andinfiltration were absent.

(f) (56). Xanthophoroma in Hyla arborea. The animal hadan orange mass behind the right tympanic membrane. Thetumor was made up of large epithelial cells and single or multi-nucleate giant cells, all of which contained orange-yellow pigment in the cytoplasm. The tumor was abundantly vascular-ized and showed hemorrhage and local necrosis. Stolk wasuncertain whether this was a true neoplasm or a granulomatousreaction to injury.

Elkan (10): considered four cases of Anuran cancer.(a) Pulmonary carcinoma in Bufo calamita. An adult female

refused food, became emaciated, and died. White nodules, 1-2mm. in diameter, were found in both lungs, and sections revealed an adenocarcinoma invading the alveoli and fillingthem.

(Â¿>)Renal carcinoma in Xenopus laevis. The animal stoppedfeeding, and its abdomen became swollen. On dissection a largetumor was found, lying retroperitoneally, in continuation withthe left kidney and pushing the intestines forward. Sectionsshowed the lesion to be a typical adenocarcinoma which haddestroyed most of the kidney.

(c) Pelvic fibroma in Xenopus laevis. A large adult femaledied and was found to contain a firm, pale tumor near thebladder and attached to the pelvic wall. It had little cellularstructure, consisting of layers of poorly staining tissue withsome nuclei at the periphery and none at the center. Elkanwondered if the tumor had arisen as a defense against cercarÃa.

(d) Facial fibromata mXenopus laevis. An adult female, with

many tumors near the external nares, stopped feeding and died.Sections showed no evidence of malignancy, but a widespreaddestruction of the maxillary region of the skull, which, nodoubt, prevented feeding.

Stolk (59-61): observed on the dorsal surface of eight adulttoads (Bufo bufo japonicus] circumscribed nodular swellingsconsisting of fusiform fibroblasts surrounded by interlacingbundles of connective tissue fibers. The tumors were similarto those described in Triturus taeniatus (Stolk, 1958, etc.) inthat the same four phases of development were apparent, andtransplantation experiments and those involving the inhibitoryeffect of colchicine gave similar results.

TUMORSIN URODELATeutschlaender1(62) : mentioned a melanosareoma of skin in

Siredon mexicanum.Broz (3) :discovered a female newt (Triturus taeniatus) with

islets of cartilage-like tissue in the stratum spongiosum coriion the side of the trunk, behind the head, and on the right hindlimbs. The blets appeared to be tumorous, probably chondro-mas, and were benign. No mÃ©tastaseswere found in otherorgans.

Rickenbacher (34) : described an ulcerated pseudo-adenoma-tous carcinoma in a female newt (Triturus alpestris). The tu-

1Since Teutschlaender (62) mentions the melanosareoma ofthe Axolotl only in his Table I and II, it is possible that thisis mistaken reporting of the melanoma of Axolotl reported byKrontovsky (1916, see Finkelstein [12]), whose work is listedin the references but not cited in the text or tables ofTeutschlaender's paper.

Teutschlaender also mentioned the following neoplasia, butwithout giving any details:

Anura: Hyla sp.â€”carcinoma of skin-glands.Urodela: Newtâ€”carcinoma of testis.

Salamanderâ€”fibroma of heart.These last three cases are not included in the tables in the

present paper.



BALLSâ€”SpontaneousNeoplasms in Amphibia 1145

mor, situated on the head, invaded the skin and the right OSnasale. The tumor was of slow growth and there were no mÃ©tastases. The author considered that the neoplasm originatedin the skin glands.

Sheremetieva-Brunst (48, 44): found a richly vascularizedtumor on the upper jaw of an adult black axolotl (Siredonmexicanum). The tumor, an epithelioma, grew rapidly until theanimal died 2 months later, having refused food and lostweight. Fragments were transferred into 21 animals, in fourteenof which tumors developed. Pieces of the most rapidly growingtumor were transferred into albino axolotls and increased insize in 85 per cent of them. The most actively growing tumorscaused loss of appetite in their hosts, but no mÃ©tastaseswerefound in the viscera at autopsy.

Inoue (16, 17): found sarcomas in an adult male newt(Triturus pyrrhogasler), consisting of a large tumor of the liver,measuring 1.1 X 0.7 X 0.4 cm., and 37 smaller nodules in theliver and spleen. The tumor was made up of a stroma and cellswith large polymorphic or smaller round nuclei. The tumorhad invaded blood vessels. Transplantation experiments weresuccessful when: (a) fragments were put into the abdominalcavity of other newts; (6) centrifuged supernatant of implantswas injected into other newts; (c) tumor fragments, stored inglycerine/saline for 34 days at room temperature, were ground,centrifuged, and injected into other newts.

Mori (24) : records post-mortem examinations of two newts(Triturila pyrrhogaster) containing liver sarcomas. In one casewere found a large white mass, 8 cm. in diameter, and eightsmaller nodules. The neoplastic cells were smaller than normalliver cells, and their cytoplasm was less stainable.

Stolk (52, 53, 57, 58): observed in adult newts (Tritunistaeniatus) firm, irregular nodules consisting of fusiform fibro-blasts and collagenous connective tissue fibers. Four phaseswere distinguishable in the development of these fibromas:(a) enlargement of the nodular swellings of the adenoepidermalreticular network; (6) continued enlargement of the nodularswellings and concentration of fibroblasts in the vicinity of theswellings; (c) formation of new fibrils from the swellings, sothat round about the fibroblasts a densely structured networkis formed; and (d) fusion of the concentrated masses of fibroblasts to form the small tumor nodules.

Small pieces of tumor tissue of nineteen newts were eachtransferred to a normal area of the same animal. In thirteenof these newts a distinct tumor of the same histolÃ³gica!typedeveloped after 3 weeks at the site of transplantation. In sixcases, the transplant was resorbed. A further series of experiments showed that colchicine had an inhibitory effect on thegrowth of similarly transplanted tumor fragments.

Schlumberger (37) : described a lobed tumor measuring 3 X4 cm. and found on the ventral part of the kidney in Necturusmaculosus. On microscopic examination, the tumor was foundto be an adenocarcinoma.

NEW CASES2

MATERIALSANDMETHODSIn spite of recent publications on the pathology

of the Amphibia (Schlumberger [37], Elkan [10],and Reichenbach-Klinke [33]), little is known ofthe anatomy and histology of nonparasitic diseasein these animals. The cases to be described occurred in the colony of animals of the genusXenopus of the Embryology Laboratory, Department of Zoology, Oxford University. During 14months, 28 animals died of disease, including twocases of vascular hamartoma, two of hematoma,

one of granuloma, and six of neoplastic disease.Tumors were found in Xenopus fraseri, Xenopuslaevis laevis, and in two animals created by em-bryological technics. The six tumors were identified as a subcutaneous lipoma and five cases oflymphosarcoma, one with lymphocytic leukemia.The animals in question were fixed in formalin,Worcester's fluid or Zenker's fluid. Paraffin sections were cut at 5-12 ^ and stained with Mayer's

Acid Haemalum and Eosin.

CASENUMBER1 : Xenopus laevis laevis.â€”Lipoma

A large adult female imported from Cape Towndeveloped a prominent, dorsal lump. On dissectiona subcutaneous mass was found, measuring about2 cm. in diameter and having the appearance offat-body tissue (Fig. 1). The mass was encapsulated, little vascularized, and joined to the rightfat-body by a connection passing through thedorsal muscles of the body wall and into the abdominal cavity. The left fat-body and viscerawere normal. The animal was fixed in Zenker's

fluid.Sections confirmed that the growth consisted of

fat-body tissue. Such a growth could have arisenfrom a developmental hamartoma, by acquiredhyperplasia, or as a result of traumatic damage.However, since the animal appeared normal onarrival, it seemed more likely that this was a truelipoma. Neither of the special features mentionedby Willis (67) were apparent, viz.: (a) mixturewith fibroblastic or other mesenchymal tissue, or(6) incorporation of other tissues within thetumor.

Tumors of adipose tissue are relatively commonin animals. Feldman (11) mentions examples inalmost all domestic animals, and Willis writes oftwo cases in dogs and one in a parrot. Schlumberger and LÃ¼cke(38) reviewed seven reports oflipoma in fishes, including four subcutaneouslipomas, one within the ventral trunk musculature,one projecting into the posterior body cavity, andanother on the lower border of the liver.

CASENUMBER2 : Xenopus laevis victorianus/Xenopus laevis laevis

The first case of lymphosarcoma was found inan animal produced by Dr. J. B. Gurdon (15), whotransferred a blÃ¡stula nucleus of Xenopus laevisvictorianus into an enucleated egg of Xenopuslaevis laevis. An apparently normal frog developed.When 10 months old, the animal suddenly becameedematous in the head, abdomen, and legs, and

2Four of the cases have been briefly summarized elsewhere(Balls [1]), and are here numbered differently.




died. Dissection showed that this female had manyeggs in one ovary and few in the other. The kidneywas much enlarged, and nodules were scattered onthe outer surfaces of both lungs. In addition, tworound lumps were found in the mesentery near thestomach. The body was fixed in 5 per cent neutralformalin. Histological study gave the followinginformation :

Kidney.â€”The kidneys were very swollen andwere being destroyed by the widespread infiltration of lymphoid cells (Fig. 2). These cells were ofa small, uniform size, spheroidal, and with littlecytoplasm but round nuclei staining deeply withthe Haemalum. The left kidney contained fewintact tubules ; those of the right kidney persistedonly in the periphery and were widely spaced, butfragments of the destroyed tubules were foundamong the lymphoid cells. Few red blood corpuscles were present as compared with those innormal kidney, which might explain the widespread necrosis within the lymphoid tissue. Invasion of blood vessels was also observed.

Lung.â€”The lungs contained many cells similarto those replacing the normal tissue of the kidneys.These cells were destroying the lung epitheliumand enlarging the organ as a whole. Erythrocyteswere conspicuously few, and necrosis was morewidespread than in the kidneys.

Liver.â€”Sections of the liver showed very largenumbers of tumor cells mixed with liver parenchyma cells. Pigment, a striking feature of thenormal liver, was almost completely absent.Erythrocytes were common and uniformly spreadthroughout the tissue, but many of the lymphoidcells were necrotic.

Mesenteric nodules.â€”The two mesenterio nodules were each about 3 mm. in diameter, composedof lymphoid cells with foamy cytoplasm, andshowed much necrosis. Erythrocytes and oddpatches of pigment were also present. The nodulesappeared to have no limiting capsule.

A small piece of fat-body was incidentally sectioned with the kidneys and contained tumorcells, although the invasion was not so marked asin cases 3 and 4.

The widespread occurrence of the round uniform cells, similar to mature lymphocytes, showing diffuse infiltration and destruction of the normal tissues of the kidneys, lungs, and liver, led tothe conclusion that this was a case of malignantlymphosarcoma. A notable feature of the tumorcells was the lack of mitosis and the frequent occurrence of necrosis. The question whether thepresence of lymphosarcomas in many tissues isdue to multifocal origin or the metastatic spreadof cells has been much discussed. Willis (67, p.

774) considers that the occurrence of lympho-sarcomatous invasion in sites other than thelymphoid structures themselvesâ€”i.e., the liver,lungs, heart, kidneys, or skinâ€”is abundant evidence that metastasis occurs, but that studies ofearly lesions show that tumors also arise multi-focally. In any event, the infiltration of liver,lungs, and blood vessels in the present case suggests that metastasis had occurred, the tumororiginating in the kidneys or the mesentericnodules.

CASENUMBER3 : Xenopus fraseriâ€”Lymphosarcoma

Juvenile animals imported from the Congo inthe summer of 1960 were later identified as Xenopus fraseri (Boulenger). One female died in March,1961, and was found to have many white noduleson the ovaries and fat-bodies. The viscera werefixed in Worcester's fluid.

Microscopic evidence of neoplastic change wasfound in the ovary, gut, and fat-body. Theseorgans will be discussed in turn.

Ovary. (Fig. 3).â€”The main ovarian nodulemeasured 0.5 cm. in diameter and was found toconsist of a mass of uniform, small lymphocyte-likecells with round nuclei and little cytoplasm. Onlythe cells around the few fairly large collections oferythrocytes seemed viable; otherwise there werehuge areas of necrosis, no doubt because the tumor was outgrowing the blood supply. On one sideof the mass were egg cells surrounded by the tumor cells. The tumor mass also contained manypolymorphonuclear leukocytes.

Gut. (Fig. 4).â€”The duodenal region of thealimentary canal showed a mass of tumor cells invading between layers of the circular musclealong about one-third of the circumference of thesection. A large piece of circular muscle had beenpushed to the outside of the tumor mass, whichalso contained pancreatic cells. The tumor cellswere similar to those in the ovarian mass, butthere was much less necrosis, many groups oferythrocytes being uniformly spread throughoutthe tissue.

Fat-body. (Fig. 5).â€”The nodules on the fat-bodies illustrated very well the diffuse infiltrativegrowth of the lymphosarcoma. Figure 5 showsthree nodules on the outside of one of the branchesof the fat-body. The tumor cells were spreadinginto the organ from the outside, moving betweenthe fat-storing cells accompanied by erythrocytes.Macroscopical examination had shown that thefat-bodies were covered with such nodules. Theonly previously described tumor affecting the fat-



BALLSâ€”Spontaneous Neoplasms in Amphibia 1147

body of an amphibian was the transplantable sarcoma of Rana pipiens described by Rose (35).

The normal tubular structure of the kidney wasunchanged.

The difference in viability between the tumorcells of the ovarian mass and those invading theintestine and fat-bodies suggests that the tumormay have originated in or near the ovary andthat the other areas were affected as a result ofmetastasis. In the light of the above histologicalfindings the tumor was diagnosed as a malignantlymphosarcoma.

CASENUMBER4 : Xenopus fraseriâ€”Lymphosarcoma

A second Xenopus frÃ¤sen died and was dissected. The intestine, liver, kidneys, and fat-bodies were covered in a multitude of whiteswellings of various sizes. The viscera were fixed inWorcester's fluid.

Macroscopical examination of the viscera ofthis animal clearly indicated advanced tumorousgrowth. The intestine was, from stomach to rectum, completely covered with white lumps and inplaces was swollen to twice the normal size. Theliver bore five white masses, which seemed to bespreading over its surface, and fifteen smallernodules. The fat-bodies were covered with manysimilar nodules. Adjacent to the kidneys were fourlarge, white vascularized bodies in the positionnormally occupied by the testes, yet oviductswere also clearly present. The results of histological examination were as follows:

Alimentary canal.â€”Transverse sections in thestomach region showed a mass of small, uniform,lymphocyte-like cells similar to those described incases 2 and 3. These cells, mixed with pancreaticcells, formed a mass equal in size to the stomachand adjacent to it. The stomach itself appearedrelatively normal.

The duodenum was seen to have its normalstructure on the whole, but some tumor cells werecontained within the villi. Outside the muscularisexterna was a large mass loosely attached to theduodenum. This mass contained many of thelymphoid cells together with pancreatic cells andone large group and several smaller groups ofblood cells. The blood cells were not limited bya cellular wall but did not contain large numbersof the lymphoid cells.

A further part of the intestine was found tohave been completely replaced by tumor cells(Fig. 6). The mucous membrane and submucosahad been destroyed, leaving only the lymphoidcells maintaining the shape of the villi and fragments of the epithelium inside the lumen, together

with erythrocytes. Two large portions of themuscularis externa remained, and further fragments were seen among the tumor cells. Necroticlymphoid cells were found toward the center ofthe nodules, but those near the groups of bloodcells appeared to be very viable.

A lower region of the intestine had a tumornodule on one side, cells from which had replacedthe nearby muscularis externa and the entiremucous membrane and submucosa, but had leftthe muscularis externa intact for the other threeparts of its circumference. Within the lumen wereloose tumor cells and erythrocytes, together withcellular detritus.

Sections in the rectal region showed thatlymphoid cells had replaced the normal rectum, ofwhich only a few muscular and epithelial remnantsremained. An unidentified parasite was found inthe lumen, but was not thought to be directly connected with the general pathological condition ofthe animal.

Fat-body.â€”Nodules on the outside of the fat-bodies were seen to have given rise to neoplasticcells invading between the fat-storing cells. Thiscondition was similar to that described in Case 3and illustrated by Figure 5.

Liver.â€”Part of the liver bearing a large, whitenodule showed that the nodule consisted of a massof lymphoid tumor cells which were invading thenormal liver tissue (Fig. 7). Also present weresmall groups of tumor cells throughout the rest ofthe liver, a demonstration of the diffuse, infiltrating spread of this type of tumor (Fig. 8). The livercontained much less pigment than occurs in thenormal liver of Xenopus, and the pigment presentwas confined to the relatively normal tissue, beingabsent from the tumor nodules (Fig. 7).

Lung.â€”The lung contained large numbers oftumor cells, both in the lumen and infiltratingfrom the periphery and destroying the muscularbasis of the lung epithelium. The center of the lungcontained many erythrocytes, but tumor cellswere predominant toward the outside.

Kidney-gonad region.â€”This region was of special interest in view of the presence of four, white,testis-like bodies as well as oviducts. Microscopical examination of the stained preparationsimmediately confirmed that the animal was ahermaphrodite. The bodies below the kidneys werefound to be two testes and two enormous nodulescomposed of tumor cells and of a diameter equal tothat of the kidney. Figure 9 shows part of theposterior half of the left kidney together with anapparently normal, sperm-containing testis. Thekidney was relatively normal, but groups of tumor cells were present near the periphery. Figure




10 shows the anterior part of the right kidney, apiece of ovary containing oocytes, an oviduct, andone of the tumor nodules. This part of the kidneywas less normal, tumor cells invading from theglomerular region toward the tubules, though theblood vessels did not appear to have been invaded.The nodule of tumor cells showed greater differentiation than in any of the other previously described regions. The density of the lymphoid cellsvaried in different parts of the nodule to give afollicular appearance somewhat like a mammalian lymph node (Fig. 10). Circumscribednodes of lymphoid tissue, however, are notnormally found in amphibians (see "Discussion").

Other regions of the gonads showed invasionand less normality in the testicular tissue, that theovarian and testicular tissue were connected, butthat the gametes were not intermingled.

The above histological description clearly indicates that this was a further case of lymphosar-coma. From the information given by the sectionsof the alimentary canal, fat-body, liver, and kidney, it would appear that the distribution of thetumor throughout the visceral organs was the result of metastatic spread, the tumor cells infiltrating inward from the outside of the organs. Earlystages in this spread could be seen in the liver (Fig.8), fat-body, kidney, stomach, and duodenum.The eventual result was shown by the mid-gut(Fig. 6) and the rectum. The large size and greaterdifferentiation of the two nodules near the kidneymight be taken to suggest that this was the originalsite of the tumor, especially since the mid- andhind-gut were the regions where invasion had proceeded to the greatest extent and were situatedimmediately ventral to the nodules.

It is impossible to say whether the hermaph-roditism was in any way connected with thepresence of neoplastic cells throughout the viscera.

CASENUMBER5 : Xenopus laevis laevisâ€”Lymphosarcoma

A female Xenopus laevis laevis containing Xenopus laevis victorianus germ-cells was produced byDr. A. \V. Blackler (2). When about 17 monthsold, the animal developed three rapidly growingtumors anterior and posterior to the right eyeand at the left angle of the jaw.

Dissection of the abdomen showed that theviscera were of normal appearance. The head withthe tumors was fixed in Zenker's fluid, and the

rest of the animal was preserved in 5 per centformalin. Examination of the head tumors gavethe following information.

a) Tumor anterior to right eye.â€”The epidermisabove the tumor was found to be relatively normal,

but the glands of the dermis were absent orruptured, perhaps by the pressure of the rapidgrowth beneath it. Below the remains of the dermis was a red mass of small, lymphocyte-like cells(Fig. 11) similar to those described in cases 2, 3,and 4. The nuclei of the cells were round andabout the size of erythrocyte nuclei, but surrounded by much less and more faintly stainingcytoplasm. The lymphoid cells were arranged inlarge groups containing few erythrocytes and weresurrounded by less dense tissue with many moreerythrocytes and the remains of the replacedmuscle. Two particularly large groups of erythrocytes contained many of the lymphoid cells.

fr) Tumor posterior to the right eye and destroying the pterygoides and temporalis muscles.â€”Thedestruction of the muscle tissue was more complete in this region than in region a, there beingmany large groups of tumor cells with little muscleand few erythrocytes. The skin above the tumorwas intact and normally colored.

c) Tumor at left jaw angle.â€”Thetumor at theleft jaw angle was found to have destroyed thenormal tissue from the skin below the jaw throughthe submaxillary muscle to the lining of themouth. The ventral skin was ulcerated in aboutfifteen places, the edges of which were coveredwith pigment cells. The mucous membrane of thefloor of the buccal cavity had about ten similarulcÃ©rations,and in places the tumor cells couldbe seen invading the outer epithelial layer (Fig.12). The general appearance of the tumor betweenthe skin and mouth lining was similar to that oftumor 6. The tumor cells were grouped in verylarge numbers, among which were the remains ofthe muscle.

Microscopical examination revealed no abnormality in the lung, ovary, ventricle, spleen,or intestine. The liver sections showed manysmall groups of lymphoid cells among the liverparenchyma, but replacement of the normal tissuewas not advanced. The extent of invasion of thekidney was variable. The glomeruli containederythrocytes and lymphocytes in equal numbers.Some tubules were surrounded or replaced bylymphoid cells.

Thus from histological observations the tumorwas diagnosed as a lymphosarcoma affecting themuscles of the head, and the liver and kidney. Inview of the very rapid growth of the head tumorsand the variable degree of infiltration of the kidney, it would appear that the tumor originated ineither of these regions and that the invasion of theliver had just begun. The tumor proved to betransplantable, as will be discussed elsewhere.




CASE NUMBER 6: Xenopus laevis laevisâ€”Lymphosarcoma

A female Xenopus laevis laevis was found tohave rapidly growing swelling on the side of thehead behind the right eye. The skin had manylight patches, but that in the region of the tumorappeared normal. When the skin was removed, theswelling was seen as a white mass of firm consistency, which was replacing the temporalis anddepressor mandibularis muscles on the right side.When the abdominal cavity was opened, theviscera appeared normal, although the liver wasunusually large and the fat-bodies were small. Theregion containing the tumor was fixed in Zenker's

fluii!, and the rest of the animal was preserved in5 per cent formalin.

Microscopic examination of the abnormalregion of the head showed that the musculartissue had been completely replaced by lymphoidcells of a uniform, small size, with large roundnuclei and little cytoplasm. The tumor showedlittle sign of differentiation (Fig. 13), the largespaces among the lymphoid cells not being limitedby an epithelium. Sparse fragments of muscle remained, and a few erythrocytes were scatteredthroughout the tissue. Particularly interesting wasthe fact that most of the erythrocytes present werecontained in arteries which had not been invadedbut contained many tumor cells. Figure 14 showssuch a vessel surrounded by spheroid tumor cells.This suggested that the tumor cells had enteredthe blood vessel during its passage through another part of the tumor or that blood-borne metastasis had occurred. The results of the microscopic examination of the viscera were as follows :

Liver.â€”Sections of the posterior part of theright lobe indicated that the normal liver tissuehad been almost completely destroyed by lymphoid cells. The remnants of the liver parenchymawere seen between large groups of neoplasticcells, but the usual, large amount of pigment waspresent. The blood vessels contained many lymphoid cells as well as erythrocytes.

Kidney.â€”The destruction of the kidney hadproceeded to a state intermediate between thoseobserved in cases 2 and 4. The tubules were stillclearly present but were surrounded by lymphoidcells which could be seen replacing the cells liningthe tubules.

Lung.â€”Although the outer muscle of the lungwas intact, the whole respiratory epithelium wascovered by a mass of lymphoid cells with someerythrocytes. Large groups of lymphoid cells wereseen in the lumen.

Spleen.â€”The spleen contained large groups of

lymphocytes, which make up the white pulp of thenormal organ, but both the red pulp and the bloodvessels contained a predominance of lymphoidcells instead of erythrocytes.

Ovary.â€”Sections of the ovary showed thatlymphoid cells were present both in the stromaand replacing the follicle cells around the oocytes.In some cases (Fig. 15) oocytes had been invadedand contained lymphoid cells and erythrocytesamong the yolk platelets.

Ventricle.â€”The muscle of the ventricle had notbeen invaded by the lymphoid tumor cells, but theblood present within the heart was composed ofapproximately equal numbers of erythrocytesand lymphocytes.

Thus, examination of the viscera showed widespread infiltration of and destruction by the lymphoid cells. The tumor cells of the viscera appearedto have entered via the blood-system, since thecapsules of these organs were intact and withoutthe white nodules described in cases 3 and 4.Furthermore, the blood itself was highly abnormal.Counts of the blood within the ventricle and theblood vessels of the head tumor, liver, lung, andkidney gave a ratio of 1.2 lymphocytes to oneerythrocyte. This is outstandingly different fromthe normal ratio in Anurans, which is one leukocyte: more than 300 erythrocytes, lymphocytesrepresenting 19-50 per cent of the leukocytes(Schlumberger [37], p. 773).

As a result of the presence of malignant lymphocytes in the circulating blood, this case wasdiagnosed as one of lymphosarcoma with lympho-cytic leukemia. Since the condition was so advanced at the time of dissection, it is impossible tosay whether the tumor originated at any one siteof blood formation or simultaneously in manyplaces. In fact, it would seem better to call this acase of "lymphosarcomatosis"â€”a generalized and

widespread involvement of lymphoid tissuethroughout the body (Willis [67], p. 769). As far aswe are aware, no case of lymphosarcoma withlymphocytic leukemia has been previously reported in an amphibian.

DISCUSSIONTumors of lymphoid tissue are among the most

common tumors of many animal species. Furthet al. (13) have demonstrated a close resemblancebetween the lymphoid tumors of man and those ofother mammals, but Willis (67) is doubtful of theanalogy between avian and mammalian lymphoiddiseases.

Fish and amphibians have no lymph nodes assuch, circumscribed collections of lymphoid tissuebeing confined to mammals and some birds.




Hematopoiesis occurs mainly in the spleen, kidney, and intestinal submucosa in these lowervertebrates, but the bone marrow may also be asource of red cells in amphibia, as, for example, inRana temporaria (Young, 68). Therefore, muchcaution is necessary when comparing the lymphoid diseases of amphibia and man.

Schlumberger and LÃ¼cke (38) mention sometwenty cases of lymphosarcoma in fishes but consider that many other cases of sarcoma may havebeen tumors of lymphoid tissue. Fifteen were lym-phosarcomas of kidney, with a tendency to metas-tasize to the liver and spleen. The others weretumors in the branchial region, peritoneum, orbit,and under the skin.

TABLE 2

SITESAFFECTEDIN THEFIVECASESOFLYMPHOSARCOMA

CABENÃ¼

SITESkinMuscle

ofheadBuccalcavityLungHeartLiverGutKidneyFat

-bodiesGonadSpleenNodules

in abdominalcavityBlood2â€”â€”+?+â€”+â€”â€”â€”+Sâ€”â€”â€”â€”?â€”+â€”++â€”â€”~4â€”â€”â€”+?+++++â€”+~t+++â€”â€”+â€”+â€”â€”â€”â€”_aâ€”+â€”+â€”+â€”+â€”++â€”+

? = unknown; â€”= negative; + = positive.

The only previous record of spontaneous lymphosarcoma in an amphibian is that of Inoue (16,17). Nodules were found in the liver and spleen ofan adult newt (Triturus pyrrhogaster), and, on thebasis of transplantation experiments, Inoue decided that the tumor was a kind of lymphosarcoma.

Tumors of hemopoietic tissue have been induced, however, by chemical carcinogens. Leone(19) induced lymphosarcomas of the liver andspleen by placing methylcholanthrene crystalsunder the skin of newts (Triturus cristatus). Thetumors showed metastasis to the limbs and visceraand were transplantable.

The occurrence within 1 year of five cases oflymphosarcoma in a stock of frogs of the genusXenopus was surprising, in view of the sole previous report of Inoue. The five animals were kept infour separate aquariaâ€”only the two Xenopus

fraseri having been kept togetherâ€”and one has

no evidence of any infective agent. The destructionof normal organs in the Xenopus fraseri was particularly advanced. In one animal the gut, ovary,and fat-bodies were being invaded, the gut, liver,fat-bodies, kidneys, and gonads in the other. Sincethe viscera were being invaded from the outerperitoneal covering, it would appear that thelymphoid cells were carried in the fluid of the bodycavity. This is clearly different from case number6, where the blood was the probable means of transportation, leading to equally extensive infiltrationof the visceral organs.

Table 2 summarizes the sites affected by lymphosarcoma in the five animals. Four of theanimals were female, and one was hermaphrodite,although the stock of Xenopus contains a largenumber of males. The most frequently affectedorgans were the kidney and liver.

Any discussion of neoplasms in amphibiansmust consider certain facts which dominate thesubject and are as yet unexplained. They are asfollows :

1. The small number of reported cases. Schlumberger and LÃ¼cke (38) considered some 300 reports of tumors in fishes, but only 29 in amphibians.

2. The small number of species in which tumorshave been observed.

3. The lack of observations of tumors inurodeles as compared with anurans.

4. The high rate of skin as compared withvisceral tumors.

5. The lack of tumors of hemopoietic tissues orof pigment cells.

We believe that the six new cases described andimportant work of Stolk, Elkan, Inoue, and others,published since the 1948 review, add so much toour knowledge of amphibian tumors that a uniqueopportunity of discussing the above points is nowpresented.

1. The small number of reports.â€”The rarity of

tumors in amphibians has been widely discussed,and many explanations have been put forward.Some consider that the amphibians are merely lesssusceptible to tumor formation than the otherclasses of vertebrates. Others have suggested thatthe regenerative ability of newts may prevent uncontrolled cancer growth, the retention into adultlife of highly potent morphogenetic fields forcingaberrant cells to differentiate by the organizereffect of adjacent tissues. Skapier (45), havingdissected 30,000 toads without finding a singlespontaneous tumor, suggested that the toadvenom might give immunity against spontaneousor induced tumors. Yet one considers that none of




these explanations is adequate, but rather thatother biological factors and a general lack of observation are involved.

The 1948 review contained discussions of 29reports of tumors in amphibians, and the presentone considers 58â€”a twofold increase. Of the 29new reports, nineteen result from the work of threeauthors, which suggests that tumors do occur butare seldom identified and described.

Age and maximum length of life must also betaken into account. Reichenbach-Klinke mentions estimations that the maximum lengths oflife of amphibians range from 10 to 40 years according to species, but that one Megalobatrachusmaximus lived in Amsterdam Zoo for 52 years.Cancer, however, is mainly a disease of the aged,but few frogs would live to old age in the naturalenvironment with the hazards of prÃ©dation,parasitism, and other diseases. In this connection it isinteresting that many of the known amphibiantumors have occurred in animals kept in zoological gardens. Furthermore, one suspects thatfew of the animals used in laboratories all over theworld are kept after their useful lifetime and thatfew workers are able to turn from their specialresearch to the study of pathology.

2. The species distribution of amphibian tumors.â€”Theearly descriptions were mainly of tumors in Rana esculenta or unidentified Ranaspecies, but more recent publications, especiallythose of Stolk, have shown that neoplasms occurin a wide range of amphibian species. The presentpaper contains the first descriptions of tumors inXenopus fraseri (Boulenger) and in animals created by embryological technics.

The species distribution of amphibian neoplasms is summarized in Table 3. In this table(as also in Tables 4-6) each report of tumors iscounted as one under the appropriate headingregardless of the number of animals concerned.The new cases described, however, are countedseparately in view of the range of species, tumors,and sites involved.

3. The apparent rarity of tumors in urodeles.â€”Hitherto one knows of fifteen reports of tumors inurodeles and 43 in anurans. The view of Schlum-berger and LÃ¼cke,viz., that the difference in tumor incidence is due more to lack of investigationthan to any biological dissimilarity, is supportedby the fact that attempts at the experimental induction of cancer with chemical substances hasbeen far more successful in urodeles than inanurans (Leone [18â€”Table2, 19]).

4. The comparative incidence of skin and visceraltumors.â€”The 1948 review showed that more neoplasms had been reported in the skin than in all

the other organs, but Table 4 shows that 27 tumorshave now been described in the skin and 42 in theother organs. The high incidence of cutaneous tumors could be due to a special susceptibility inthis region which, especially in the amphibia, isthe center of so much metabolic activity and is inclose contact with the external environment. Onthe other hand, it may merely be that abnormali-

TABLE 8

SPECIESDISTRIBUTIONOFAMPHIBIANTUMORS

SPECIES No.REPORTS

Anura

Rana sp.Rana virescensRana esculentaRana pipiensRana caiesbÃ¬anaRana temporariaRana fuscaRana clamitansRana arvalisCeratophrys ornataIlyla arboreaHyla arborea merÃ¬dionalisDendrobates typographicusXenopus fraseriXenopus laevis laevisXenopus laevis victorianus/Xenopus

laevis laevisBufo bufoBufo bufo japonicusBufo marinusBufo calamitÃ

Urodela

Triturus cristatusTriturus alpestrisTriturus pyrrhogasterTriturus taeniatusSiredon mexicanumMegalobatrachus maximusNecturus maculatila

ties of the skin are so much more easily noticed inthe living animal.

It is interesting that the kidney should be themost common site of visceral tumors, the fourteenreports including adenocarcinomas of kidney inXenopus laevis and Necturus maculatus, as well asin Rana pipiens. Of the five lymphosarcomas described above, four involved the kidney, which isthe main site of hemopoiesis, whereas the othercase and that of Inoue did not. The two lymphosarcomas which were destroying the muscles ofthe head region were both of very rapid growth.




This argues against the opinion that amphibiantumors are of slow growth as a result of their lowmetabolic rate.

5. Tumors of hemopoietic tissues and of pigmentcells.â€”Notumors of hemopoietic tissues had beenfound in amphibia up to the time of the Schlum-berger and LÃ¼ckereview. This position has beenmarkedly altered by the work of Inoue, Leone, andthe reports in the present paper. Indeed, it is clearthat, when tumors of lymphoid tissue occur inamphibia, they are especially invasive and destructive.

Melanosarcomas have often been found inSiredon mexicanum and are notable because of

TABLE4SITESOFAMPHIBIANTUMORS

SITESkinMuscles

ofheadBuccalcavityFaceParotid

glandLegFemurPalmTail

(tadpole)PelvisSacral

plexusLungHeartLiverGutKidneySpleenFat-bodyTestisOvaryBloodANCHANo.

reporta172211311115172132331Per

centoftotalno.

reports25.53.03.01.51.54.51.51.51.51.57.51.510.53.019.53.04.54.51.5URODELANo.reports10121111Per

centoftotalno.

reports58.85.911.85.95.95.95.9

their genetic significance (Sheremetieva-Brunstand Brunst [41]). No tumors of pigment cells wererecorded in anurans, however, until Stolk described an erythrophoroma in Dendrobates typo-graphicus, a guanophoroma in Hyla arborea meri-dionalis, and a xanthophoroma in Hyla arborea,and Rostand (36) found a melanic tumor in Ranatemporaria.

Table 5 gives a classification of tumors recorded in amphibians, based on that of Willis(67, p. 17). When compared with that of Schlum-berger and LÃ¼cke,this table clearly illustrates theincrease in our knowledge of amphibian tumorssince 1948.

Table 6 is an attempt to summarize the spontaneous neoplasms in Amphibia. Of the tumors re

ported to date more were malignant than werebenign. Most of the malignant tumors were described as invasive, but less than one-third ofthem showed metastasis. Many of the animalsconcerned were found only after death. Attempts

TABLE 5

TUMORSOFAMPHIBIA

Ti M. .HGBOUPTumors

of epithelialtissuesTumors

ofnonhe-mopoieticmes-encbymal

tissuesTumors

of hemopoietictissuesTumors

ofneuraltissuesPigment-cell

tumorsAngiomasOther

tumorsTOMOBAdenomaAdenocarcinomaHepatomaHypernephromaCarcinomaAdenoepitheliomaEpitheliomaFibromaFibrosarcomaMyxosarcomaMyxofibrochondromaOsteogenic

sarcomaLipomaSarcomaChondromaLymphosarcomaNeurosarcomaMelanomaMelanosarcomaXanthophoromaErythrophoromaGuanophoromaHemangiomaCapsulated

tumorNo.

REPORTSAnura791121411111151111111UrodelaZ31311121

TABLE 6

SUMMARYOFPRESENTKNOWLEDGEOFAMPHIBIANTUMORS

Total number ofreportsMalignanttumorsBenigntumorsTumors

showinginvasionTumorsshowingmetastasisTransplantation:Not

attemptedSuccessfulattemptswith

malignanttumorswithbenigntumorsUnsuccessful

attemptswithmalignanttumorswithbenign tumorsAnuÃ.

i432419198325

(+1)*5(+1)*523Urodela159682104(+D*3i

(+D*Total5833252710429

(+2)*81

(+2)*523

* N.B. Figures in parentheses refer to the experiments ofStolk involving transplantation to different parts of the sameanimal bearing the original tumor.




at transplantation, when possible, have beenreasonably successful.

ACKNOWLEDGMENTSThe author is particularly grateful to Professor M. Fisch-

berg for his guidance and for his interest in this work, and toboth him and to Professor A. W. Blackler for reading themanuscript. The author is pleased to thank Dr. N. F. C. Gow-ing of the Royal Marsden Hospital, London, without whoseadvice and interest this paper would not have been written.Miss M. Petersen has provided valuable technical assistance.

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50. . Skin Adenoma in Rana analiÂ»Nilson. Ibid., pp.167-83, 1957.

51. . Haemangioma of Heart in Hyla arborea. Ibid., C.61:124-29, 1958.

52. . A Transplantable Fibroma of the Skin in theNewt, Triturus iaeniaius. Experientia, 14:243, 1958.

58. . Development of the Multiple Fibroma of theAdepidermal Reticular Network in the Skin of the Newt,Triturila toeniatua. Proc. Koninkl. Ned. Akad. Wetenschap.Amsterdam, C. 61:610-30, 1958.

54. . Erythrophoroma in Dendrobotes typographicus.Ibid., C. 62:381-89, 1959.

55. . Guanophoroma in the Frog Hyla arborea meridionali*. Ibid., pp. 390-95.

56. . Xanthophoroma in the frog Hyla arborea. Ibid.,pp. 568-75.

57. . Transplantation Experiments with the MultipleFibroma of the Skin in the Newt Triturus taeniatus. Ibid.,pp. 172-92.

58. . The Inhibitory Effect of Colchicine upon the Multiple Fibroma of the Skin in the Newt Triturus taeniatus.Ibid., pp. 267-77.

59. . Development of the Cutaneous Fibroma of theAdepidermal Reticular Network in the Skin of the ToadBufo bufojaponicus. Acta Neerl. Morphol., 4:237-53,1961.

60. . Transplantation Experiments with the CutaneousFibroma of the Skin in the Toad Bufo bufo japonicus.Proc. Koninkl. Ned. Akad. Wetenschap. Amsterdam, C.63:343-61, 1961.

61. . The Inhibitory Effect of Colchicine upon theCutaneous Fibroma in the Toad Bufo bufojaponicus. Ibid.,pp. 362-74.

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64. . LÃ©sionsstomacales observÃ©eschez un Python deSeba. Ibid., pp. 593-95.

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67. . The Pathology of Tumours. 3d ed. London: Butter-worths. 1960.

68. YOUNG,J. Z. The Life of Vertebrates. 1st ed. Oxford, 1950.

FIG. 1.â€”Xenopuslaevis laeris (Case 1). Animal dissected toshow lipoma (1) in situ. X0.75.

FIG. 2.â€”Xenopuslaevis laevis/X.l. victorianus (Case 2). Replacement of right kidney by lymphoid cells. Some tubules(tu) remain toward the periphery (top right) and among thelymphoid cells. X44.

FIG. 3.â€”Xenopusfraseri (Case 3). Ovarian tumor consisting of a dense mass of lymphoid cells. Some oocytes (o) werepresent in the outer part of the tumor. X44.

FIG. 4.â€”Xenopus fraseri (Case 3). Transverse sectionshowing lymphosarcoma cells adjacent to the duodenum. X44.



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FIG. S.â€”XmopuÂ»Â¡rasen (Case 8). Lymphoid cells infiltrating between the fat-storage cells from tumor nodules outside the fat-body. X50.

Fio. 6.â€”Xenopus froseti (Case 4). Section through mid-intestinal region to show how the normal cells have been largelyreplaced by lymphoid cells. The gut lumen (gÃ¬)and muscularisexterna (m) are still visible. Note the large necrotic areas (no)within the tumor tissue. X44.

FIG. 7.â€”Xenopus fraseri (Case 4). Liver bearing a largenodule (in) composed of lymphoid cells (<), which have alsoinfiltrateti the liver parenchyma. Pigment (p), a. striking feature of the normal liver, was absent from the nodule. X44.

FIG. 8.â€”Xenopus fraseri (Case 4). Higher magnification oflymphoid cells among the parenchyma and pigment (/)) of theliver. X140.



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FIG. 9.â€”XenopuÃifraseri (Case 4). Transverse section oftestis and left kidney. The testis contained mature spermatozoa(very darkly stained). X44.

FIG. 10.â€”Xenopuxfraseri (Case 4). Transverse section ofright kidney of the same animal and of a large nodule (in) oflytnphoid cells, which somewhat resembles a mammalian lymphnode. Also present are some oocytes (o), an oviduct (op),andii large blood vessel (bv). X49.

FIG. 11.â€”Xenopunlaevis laevis (Case 5). Section throughtumor anterior to eye and consisting of a large nodule oflymphoid cells (in) and groups of lymphoid cells (f) mixed witherythrocytes. The epidermis (e), dermis (d) and some musclefragments (m) had not been invaded. X44.



1011



FIG. lÃ .â€”Xeno/iti* laeri.t laeriÂ» (Case 5). Tumor cells in

vading the epidermal layer (e) of the buccal cavity, hut leavingthe connective tissue (ct) relatively unaffected. X150.

FIG. 18.â€”Xenoput laevis laevis (Case 6). Section of the

mass of lymphoid cells replacing the head muscles, showingsome vacuolation (r). The- l>lood vessel (In') is shown in Figure

14 at a greater magnification. X48.FIG. 14.â€”Xenapus laevis laevis (Case 6). Section of blood

vessel surrounded by lymphoid tumor cells (<), but with anintact, pigmented (Â¡i)wall. Inside the blood vessel may be seenerythrocytes (pale cytoplasm) and tumor cells (dense black).X234.

FIG. 15.â€”Xenopus laevis laevis (Case 6). Section through

part of ovary showing lymphoid cells (/) among the yolkplatelets (yp) of one oocyte and replacing the follicle cells ofothers. X150.



12 13



1962;22:1142-1154. Cancer Res Michael Balls Descriptions of Six New CasesSpontaneous Neoplasms in Amphibia: A Review and

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