Malignant Neoplasms
posted in The Aging Liver |Colorectal cancer is second only to lung cancer as the most common malignancy among US and Western European men and women. In the USA, about 150,0(10 new cases of and 60.000 deaths from (his disease occur annually.
The incidence of colorectal cancer begins rising at age 40 and doubles every 5 yr thereafter, peaking in the eighth decade. Adenocarcinoma constitutes 95% of all colorectal cancers. Rectal cancer is more common in men; colon cancer apparently occurs equally in men and women. Synchronous colon cancers appear in about 3.5% of patients followed for > 25 yr, and metachronous lesions appear in 5% of such patients. Colonoscopic polypectomy in these palients will undoubtedly reduce these percentages.
Colorectal carcinoma is more common in upper socioeconomic classes. High-risk populations consume a diet higher in animal fat and refined sugar and lower in fiber than that consumed by low-risk populations. Other predisposing factors include age > 40, a history of colonic adenomatous polyps or cancer of the colon without follow-up colonoscopy surveillance, cancer of Ihe breast or female genital tract, first-degree relative with colon cancer, inflammatory bowel disease (eg, ulcerative colitis. Crohn’s disease, or radiation proctocolitis), and certain chronic parasitic infections (eg, schistosomiasis). Hereditary disorders (eg, familial polyposis) also arc associated with a high incidence of colorectal carcinoma, but they arc rare in the elderly.
The extent of tumor spread is graded by a modified Dukes classification. Dukes A lesions involve the mucosa; \i lesions extend through the wall but do nol involve lymph nodes; C lesions involve lymph nodes; and D lesions have distant metastases. Many modifications of this staging system exist.
Other colorectal malignancies include lymphoma, leiomyosarcoma, and carcinoid tumors.
Symptoms and Signs
Because colon cancer is asymplomalic in its early stages, screening is performed using routine sigmoidoscope examination every 3 lo 5 yr and annual fecal occull blood testing.
The location of a tumor in the colon influences the symptoms. Right-colon lesions are usually large, fungating. bleeding masses that cause iron deficiency anemia, fatigue, and weakness, and the large-caliber, thin-walled right colon contains fluid-like feces. These tumors usually do nol cause obstruction but may grow large enough to be palpable on abdominal examination. Left-colon lesions are usually “napkin-ring.” obstructive tumors that cause rectal bleeding, crampy abdominal pain, or altered bowel habits because of the narrower caliber of the left colon and the semisolid consistency of the feces. Patients with rectal lesions generally present with stool streaked or mixed with blood. They may also complain of tenesmus or a sensation of incomplete evacuation. Palpable lymphadenopathy, hepatomegaly, or both occur only in the late stages and suggest a very poor prognosis.
Diagnosis
Diagnosis is made by x-ray or endoscopy. A rigid sigmoidoscope may not be able to detect colon cancer because the instrument may not even reach its 25-cm iength. The fiberoptic sigmoidoscope can detect lesions in the rectum, the sigmoid colon, and the distal descending colon, the region where > 50% of cancers occur. The more proximal segments of the colon are examined by barium enema x-ray or colonoscopy. Air-contrast barium enema is usually superior lo the single-contrast technique in detecting colon cancer. Colonoscopy provides visualization and tissue for diagnosis and also allows inspection of the entire colon for synchronous polyps or cancers.
Fecal occult blood testing helps detect colonic tumors. Screening of elderly patients wilh annual fecal occult blood testing using six guaiac-impregnated slides over 3 days and sigmoidoscopy every 3 to 5 yr aids detection of early stage colon cancer, which is potentially curable. Wilh both screening tests, the positive predictive value is better in persons > 60 yr. Screening wilh fecal occult blood testing can reduce the mortality rate of colorectal cancer.
Carcinoembryonic antigen (CEA) levels may be elevated in patients with cancer of the colon, pancreas, breast, lung, prostate, stomach, or bladder as well as in those wilh benign conditions and !hus are nonspecific. An elevated CEA level is especially insensitive for early stage cancers. However, if the CEA level is elevated before surgery and decreases after it. a subsequent rise may indicate a recurrence.
Treatment
Treatment of colorectal cancer consists primarily of anatomic surgical resection (see Ch. 62). Except with lymphoma, radiation therapy ami chemotherapy do not cure. In Dukes C colon cancer and in Dukes B2 and C rectal cancer, adjuvant chemotherapy with 5-fluorouracil and levamisole combined with radiation therapy improves survival.
In patients with adenocarcinoma, the 5-yr survival r;ile is about 90% for piilienls with Dukes A lesions, 50% to 80% for those with B lesions, 30% to 40% for those with C lesions, and < 5% for those with I) lesions. Primary Gl tract lymphoma has an overall 5-yr survival rate of > 50%.
