Malignant tumors of the colon or rectum are almost always adenocarcinomas. About half of these are sessile lesions of the rectosigmoid area; the rest are polypoid lesions.

Colorectal cancer progresses slowly, remaining localized for a long time. With early diagnosis, the 5year survival rate is 50%. It is potentially curable in 75% of patients if an early diagnosis allows resection before nodal involvement.

Causes of Colorectal Cancer

Although the exact cause of colorectal cancer is unknown, studies show a greater incidence in areas of higher economic development, suggesting a relationship to a diet that includes excess animal fat, especially from beef, and low fiber.

Other factors that magnify the risk of developing colorectal cancer include diseases of the digestive tract, a history of ulcerative colitis (cancer usually starts in 11 to 17 years), and familial polyposis (cancer almost always develops by age 50).

Signs & Symptoms of Colorectal Cancer

Colorectal cancer can be asymptomatic (i.e., it may not cause symptoms). Blood in the stool is a common sign of the disease. Blood may be bright red or dark in color, and may not be noticeable. Chronic bleeding may result in iron deficiency anemia, which may cause fatigue and pale skin.

Other symptoms include the following:

Abdominal discomfort (e.g., pain, bloating, cramping, fullness)
Change in bowel habits
Constipation or diarrhea
Narrow stools
Nausea and vomiting
Unexplained weight loss

Diagnostic Tests

Several tests support a diagnosis of colorectal cancer. Digital rectal examination can detect almost 15% of colorectal cancers. Specifically, it can detect suspicious rectal and perianal lesions. Fecal occult blood test can detect blood in stools, a warning sign of rectal cancer.

Proctoscopy or sigmoidoscopy permits visualization of the lower GI tract. It can detect up to 66% of colorectal cancers. Colonoscopy permits visual inspection and photography of the colon up to the ileocecal valve and provides access for polypectomies and biopsies of suspected lesions.

Excretory urography verifies bilateral renal function and allows inspection for displacement of the kidneys, ureters, or bladder by a tumor pressing against these structures.

Barium enema studies, using a dual contrast of barium and air, allow the location of lesions that aren't detectable manually or visually. Barium examination shouldn't precede colonoscopy or excretory urography because barium sulfate interferes with these tests.

A computed tomography scan allows better visualization if a barium enema yields inconclusive results or if metastasis to the pelvic lymph nodes is suspected.

Carcinoembryonic antigen, although not specific or sensitive enough for early diagnosis of colorectal cancer, permits patient monitoring before and after treatment to detect metastasis or recurrence.

Treatment

The most effective treatment for colorectal cancer is surgery to remove the malignant tumor and adjacent tissues, along with any lymph nodes that may contain cancer cells. After surgery, treatment continues with chemotherapy, radiation therapy, or both.

The type of surgery depends on tumor location:

Cecum and ascending colon. Tumors in these areas call for right hemicolectomy (for advanced disease). Surgery may include resection of the terminal segment of the ileum, cecum, ascending colon, and right half of the transverse colon with corresponding mesentery
Proximal and middle transverse colon. Surgery consists of right colectomy that includes the transverse colon and mesentery corresponding to midcolic vessels, or segmental resection of the transverse colon and associated midcolic vessels.
Sigmoid colon. Surgery usually is limited to the sigmoid colon and mesentery.
Upper rectum. A tumor in this area usually requires anterior or low anterior resection. A newer method, using a stapler, allows for much lower resections than previously possible.
Lower rectum. Abdominoperineal resection and permanent sigmoid colostomy are required.

If metastasis has occurred, or if the patient has residual disease or a recurrent inoperable tumor, he needs chemotherapy. Drugs used in such treatment commonly include fluorouracil combined with levamisole or leucovorin. Researchers are evaluating the effectiveness of fluorouracil with recombinant interferon alfa-2a.

Radiation therapy, used before or after surgery, induces tumor regression.

Prevention Tips

Early detection and removal of intestinal polyps may help prevent colorectal cancer. Studies are being conducted to determine if reducing risk factors (e.g., smoking, daily alcohol consumption), eating a low-fat, high-fiber diet, and increasing physical activity can help prevent the disease.

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