colon and rectum

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Colon and Rectum

Anatomic Considerations and Patterns of Spread

Rectum 12 to 15 cm in lengthfrom the rectosigmoid junction to the puborectalis ringupper third middle third (posterior border of the rectouterine pouch or rectovesical space) lowest third no serosal barrier

Colonic nodal drainageconsists of pericolic nodes and nodes in association with the vascular supply to the colon (i.e., mesenteric nodesrectal nodal drainage include the perirectal, presacral, and internal iliac nodes .Epidemiology, Molecular Cascade, Risk Factors, Hereditary Disease, and Clinical Presentation

The median age is in the seventh decadechemical carcinogens Environmental and dietary factors

Factors shown to increase the risk include increasing age, male sex,rectal cancerexcessive alcohol use family history of colorectal cancer, increasing height, increasing body mass index, processed meat intakelow folate consumption.consumption of fruits and vegetables ?The role of chemopreventive agents (carotenoids, aspirin, and other nonsteroidal anti-inflammatory drugs) ?

Biologic and genetic pathways of development of colorectal cancer proto-oncogenes (mutations in the ras proto-oncogene.) tumor suppressor genes (inactivation adenomatous polyposis coli (APC) and P53)

:microsatellite instability BiologyThe majority of HNPCCas well as a minority of sporadic colorectal cancers harbor microsatellite instability.mutations in genes encoding enzymes that repair DNA replication errors Studies have suggested that patients with tumors possessing a high frequency of microsatellite instability have a more favorable outcome and develop fewer metastasesColorectal cancerminimal or no symptomsNonspecific bowel habits, weakness, intermittent abdominal pain, nausea, and vomiting. The persistence of such symptoms as well as any evidence of iron deficiency anemia should be investigatedClinical Presentationright colon exophytic ,iron deficiency anemia left colon and sigmoid colon deeply invasive, annular, and accompanied by obstruction and rectal bleeding Rectal cancer frequently results in bleeding and alterations in bowel habits.

FIGURE 58.1. Idealized depiction of peritoneal relationships in the colon and rectum. The transverse and sigmoid colon are intraperitoneal, with a complete peritoneal covering (serosa) and mesentery. The ascending and descending colon are retroperitoneal, lack a true mesentery, and usually do not have a peritoneal covering posteriorly or laterally. The upper rectum begins above the peritoneal reflection and has peritoneum anteriorly and laterally. The lower half to two thirds of the rectum is below the peritoneal reflection (infraperitoneal).

Prevention and Early Detection

Neoplastic polyps are precursors of colon cancers Most colorectal cancers arise from pre-existing polyps Patients with neoplastic polyps should be considered at high risk for large bowel cancer, and polypectomy may reduce this risk. With the availability of the flexible colonoscope and endoscopic polypectomy, polyps can be removed at a premalignant stage and patients followed closely.

The goal of screening is to detect preinvasive polyps or early invasive cancer. The presence of polyps increases the risk for cancer to approximately 15%. Data from programs in which proctoscopy is performed annually suggest that routinely scheduled polypectomy reduces the development of subsequent bowel cancer by 80% or more .

The American Cancer Society has recommended screening should begin at age 50 in the average risk patient by either:

Annual fecal occult blood test and/or flexible sigmoidoscopy every 5 years,Double contrast barium enema every 5 yearsColonoscopy every 10 yearspatients at high riskadenomatous polyps history of colorectal cancerfirst-degree relative with colorectal cancer or adenomas inflammatory bowel diseasefamily history or genetic testingIntensive surveillance is recommended for patients at high risk Computed tomography (CT) colonography genetic fecal testing are being studied Although screening methods can detect colorectal cancer at an early stage, 90%) adenocarcinomas Scc, carcinoid, leiomyosarcoma, and lymphoma.Most grading systems classify adenocarcinoma as well, either moderately or poorly differentiated.

Pathways of Spreadinvade from mucosa through the bowel wall and beyond, with involvement of lymphatic channels and lymph nodes. Hematogenous spread can occur, primarily to the lung and liver. There is little propensity for colon cancer to spread longitudinally within the bowel wall, in contrast to esophageal or gastric cancersPatient Evaluation/Staging

Pretreatment evaluation pathological confirmation colonoscopy ( synchronous primaries occurring in 3% to 5%) CBC with LFT and CEA abdominal and pelvic CT scan CXR (PET) scan (MRI), Ultrasound (PET) scan .Prognostic factorsdepth of tumor invasion into and beyond the bowel wallthe number of involved regional lymph nodespresence or absence of distant metastasesThe tumor, node, metastasis (TNM) system of the American Joint Committee on Cancer can be used as a clinical (preoperative) or postoperative staging system Colorectal Tumor, Node, Metastasis Staging, 2002Tis Carcinoma in situ: Intraepithelial or invasion of lamina propriaT1 Tumor invades submucosaT2 Tumor invades muscularis propriaT3 Tumor invades through the muscularis propria into the subserosa, or into non-peritonealized pericolic or perirectal tissuesT4 Tumor directly invades other organs or structuresa and/or perforates visceral peritoneum (includes invasion of other segments of colon)

Direct invasion in T4 includes invasion of other segments of the colorectum by way of the serosa; for example, invasion of the sigmoid by a carcinoma of the cecum. Tumor that is adherent to other organs or structures, macroscopically, is classified as T4. However, if no tumor is present in the adhesion, microscopically, the classification should be pT3N1 Metastasis in one to three regional lymph nodesN2 Metastasis in four or more regional lymph nodes (Tumor nodules in the pericolonic adipose tissue without evidence of residual lymph node are classified as a regional lymph node metastases)

Therapy of Colon CancerSurgery

based on the anatomy and mechanisms by which this disease spreads. avoid cutting across tumor in intramural lymphatics, sufficient lengths of bowel must be resected

Resection results in excellent cure ratesaverage 5-year survival 97% for T1N0 85% to 90% for T2N065% to 75% for T3T4N0 50% (T3N+) and 35% (T4N+)American Joint Committee on Cancer Stage GroupingMAC

Dukes

MNTStageAAT1IB1AT2B2BT3IIAB3BT4IIBC1CM0N1T1-T2IIIAC2/C3CM0N1T3-T4IIIBC1/C2/C3CM0N2Any TIIICD-M1Any NAny T

IVAdjuvant Chemotherapy

addition of 5FU (5-fluorouacil) and leucovorin improves survival for resected stage III patients Capecitabine, an oral 5-FU prodrug, has demonstrated similar overall and disease free survival rates to 5-FU/leucovorin in patients with resected stage III colon cancer 5-FU/leucororin/oxaliplatin in resected stage II or III colon cancer patients showed improved disease-free FU/LV/oxaliplatin as the new standard chemotherapeutic regimen in the adjuvant treatment of completely resected, high-risk colon cancerThe efficacy of agents such as bevacizumab and cetuximab as adjuvant therapy is being investigatedAdjuvant Irradiation with or without Concurrent Chemotherapy

The potential indications for adjuvant radiation therapy in colon cancer are based on analyses of patterns of failure following resection local failure in colon cancer also depends on anatomic originascending and descending colon mid-sigmoid and mid-transverse colon cecal, hepatic/splenic flexure, and proximal/distal sigmoid tumors are variable depending on the amount of mesentery present, tumor extension, and the adequacy of radial margins. When colon cancers adhere to or invade adjacent structures, local failure rates exceed 30% following surgery alone.

In summary, local failure occurs in patients with colonic tumors where there are anatomic constraints on radial resection margins, including tumors adherent to or invading adjacent structures.To summarize, these studies have suggested that operative bed failures in high-risk patients undergoing resection alone are at least 30%, and that the risk of local failure is reduced by the administration of adjuvant radiation therapy. Irradiated patients included those with T4N0/N+, T3N+ disease (excluding mid-sigmoid and mid-transverse colon) and T3N0 patients with margins of