A. Symptoms and Signs
Adenocarcinomas grow slowly and may be present for several years before symptoms appear. However, some asymptomatic tumors may be detected by the presence of fecal occult blood (see Colorectal Cancer Screening, below). Symptoms depend on the location of the carcinoma. Chronic blood loss from right-sided colonic cancers may cause iron deficiency anemia, manifested by fatigue and weakness. Obstruction, however, is uncommon because of the large diameter of the right colon and the liquid consistency of the fecal material. Lesions of the left colon often involve the bowel circumferentially. Because the left colon has a smaller diameter and the fecal matter is solid, obstructive symptoms may develop with colicky abdominal pain and a change in bowel habits. Constipation may alternate with periods of increased frequency and loose stools. The stool may be streaked with blood, though marked bleeding is unusual. With rectal cancers, patients note tenesmus, urgency, and recurrent hematochezia. Weight loss is uncommon. Physical examination is usually normal except in advanced disease. A mass may be palpable in the abdomen. The liver should be examined for hepatomegaly, suggesting metastatic spread. For cancers of the distal rectum, digital examination is necessary to determine whether there is extension into the anal sphincter or fixation, suggesting extension to the pelvic floor.

B. Laboratory Findings
A complete blood count is obtained to look for evidence of anemia. Elevated liver function tests are suspicious for metastatic disease. Carcinoembryonic antigen (CEA) should be measured in all patients with proved colorectal cancer. A preoperative CEA level > 5 ng/mL is a poor prognostic indicator. After complete surgical resection, CEA levels should normalize; persistently elevated levels suggest the presence of persistent disease and warrant further evaluation.

C. Inspection of the Colon
Cancers may be detected with a high degree of reliability with barium enema, CT colonography (“virtual colonoscopy”), or colonoscopy. Colonoscopy is the diagnostic procedure of choice in patients with a clinical history suggestive of colon cancer or in patients with an abnormality suspicious for cancer detected on radiographic imaging. Colonoscopy permits biopsy for pathologic confirmation of malignancy. In patients in whom colonoscopy is unable to reach the cecum (

< 5% of cases) or when a nearly obstructing tumor precludes passage of the colonoscope, barium enema or CT colonography examination should be performed.

D. Imaging
Clinicians obtain an abdominal and pelvic CT scan to assist in preoperative staging. CT scans may demonstrate distal metastases but are less accurate in the determination of the level of local tumor extension (T stage) or lymphatic spread (N stage). Intraoperative assessment of the liver by direct palpation and ultrasonography is more accurate than CT scanning for the detection of hepatic metastases. For rectal cancer, pelvic MRI or endorectal ultrasonography provides important accurate information about the depth of penetration of the cancer through the rectal wall and pararectal lymph nodes that may guide preoperative (neoadjuvant) chemoradiotherapy and operative management. A chest CT scan should also be obtained because the systemic blood supply of the distal rectum may promote distal tumor metastasis outside the abdomen. PET is useful to determine recurrent colorectal cancer but currently is not used for staging of primary tumors.

Colorectal cancer Differential Diagnosis
The nonspecific symptoms of colon cancer may be confused with those of irritable bowel syndrome, diverticular disease, ischemic colitis, inflammatory bowel disease, infectious colitis, and hemorrhoids. Neoplasm must be excluded in any patient over age 40 years who reports a change in bowel habits or hematochezia or who has an unexplained iron deficiency anemia or occult blood in the stools.

Staging
Determination of the stage of colorectal cancer is important not only because it correlates with the patient’s long-term survival but also because it is used to determine which patients should receive adjuvant therapy. Although the Dukes’ classification has been widely used in the past, the TNM system is now more commonly used.

Patrick Johnston, Queen’s University Belfast, Belfast, Northern Ireland, U.K.

Eric Van Cutsem, University Hospital Gasthuisberg, Leuven, Belgium

References