LETTER TO THE EDITOR

Is There a Relationship Between Colorectal and Prostate Cancer?

To the Editor--The association between colorectal

cancer and prostate cancer is debated. A literature

search provided a few articles hinting at possible

relationships; however, no direct cause or etiologic

mechanisms have been discovered.

The association of cancers can be attributed to

three possible mechanisms. First, an association will

exist if the cancers have common risk factors or etio-

logic mechanisms. Second, detection of one cancer

usually launches a thorough metastatic evaluation

that discovers other lesions, and this poses a possible

association. Third, a causal relationship between can-

cers may exist in which one cancer increases the

relative risk of the second cancer developing; this

could be caused by side effects of treatment for the

initial cancer such as radiation, chemotherapy, or pos-

sibly some direct mechanism relating to the primary

tumor. With regard to common risk factors, incidence of

both prostate cancer and colorectal cancer is in-

creased in patients who consume a high percentage

of total caloric intake as dietary fat. The mechanism of

dietary fat causing colorectal cancer has been identi-

fied; however, no etiologic mechanism between pros-

tate cancer and increased fat diet has been postulated.

Furthermore, the increased relative risks are not con-

gruent as the relationship between fat and colorectal

cancer is greater than that for fat and prostate cancer.

No other common risk factors have been identified.

The assumed association between prostate cancer

and colorectal cancer exists because there is an in-

creased incidence of prostate cancer after detection of

colorectal cancer, but there has been no statistically

significant increased number of primary colorectal

cancer demonstrated following the detection of pros-

tate cancer. This increased incidence in prostate can-

cer after detection of colorectal cancer is believed to

be due to an aggressive evaluation of the prostate

during the work-up for colorectal cancer. Prostate

cancer metastasizes to the colon in 1.5 to 11 percent

of cases, and these situations are usually initially mis-

diagnosed as colorectal cancer; this does not suggest

common etiology. In nine percent of prostatic metas-

tasis to the colon, an annular stricture of the rectosig-

moid colon occurs, which presents in a similar fash-

ion to colorectal cancer. Thus, the two cancers may be

due to their anatomic proximity and not because they

have a common etiology.

A recent study relating cancers of the small and

large bowel found an association between prostate

cancer and malignant carcinoid tumors of the small

bowel. This association was reported to have an ob-

served to expected ratio of 2:5 in both directions. One

could postulate that the production of a growth factor

for prostate cancer is produced by the carcinoid tu-

mor, yet this does not take into consideration the

increased ratio of carcinoid tumors following prostate

cancer. This recent finding may only represent a

chance finding and should be further evaluated.

No common causal mechanism has been discov-

ered to associate the incidence of prostate cancer to

colorectal cancer. Proximity of the two lesions in-

creases detection of prostate cancer following colo-

rectal cancer. Future studies of possible associations

of common mechanisms between prostate cancer and

malignant carcinoid tumors may reveal further infor-

mation on the nature of both disease processes.

REFERENCES

1. Miller AB. Diet and cancer. Acta Oncol 1990;29:87-95. 2. Maclennan R. Fat intake and cancer of the gastrointes-

tinal tract and prostate. Med Oncol Tumor Pharmaco- ther 1985;2:137-42.

3. Neugut AI, Murray TI, Lee WC, Robonsin E. The asso- ciation of breast cancer and colorectal cancer in men. Cancer 1991;68:2069-73.

4. Culkin DJ, Demos TC, Wheller JS, Castelli M, Canning JR. Separate annular strictures of the rectosigmoid colon secondary to unsuspected prostate cancer. 3 Surg Oncol 1990;43:189-92.

5. Neugut M, Santos J. The association between cancers of the small and large bowel. Cancer Epidemiol Biomark- ers Prey 1993;2:551-3.

James Simon, M.D.

Anthony M. Vemava, M.D.

Walter E. Longo, M.D. St. Louis, Missouri

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