In the United States and Europe, colorectal cancer is the second most common visceral neoplasm. Incidence is equally distributed between men and women. Colon cancer affects more than twice as many people as rectal cancer. Incidence increases with age, with most patients older than age 55. Higher incidence occurs in patients with a family history of colorectal cancer and in those who have chronic inflammatory bowel disease or polyps.
Colorectal malignant tumors are almost always adenocarcinomas. About half of these are sessile lesions of the rectosigmoid area; the rest are polypoid lesions.
Colorectal cancer tends to progress slowly and remains localized for a long time. Consequently, it’s potentially curable in 75% of patients if an early diagnosis allows resection before nodal involvement. With early diagnosis, the overall 5-year survival rate is about 50%.
The exact cause of colorectal cancer is unknown, but studies showing concentration in areas of higher economic development suggest a relation to diet (excess animal fat, particularly beef, and low fiber). Other factors that increase the risk of developing colorectal cancer include:
other diseases of the digestive tract
age (older than 40)
history of ulcerative colitis (the average interval before onset of cancer is 11 to 17 years)
familial polyposis (cancer almost always develops by age 50).
Signs and symptoms
Signs and symptoms of colorectal cancer result from local obstruction and, in later stages, from direct extension to adjacent organs (bladder, prostate, ureters, vagina, sacrum) and distant metastasis (usually to the liver).
In the early stages, signs and symptoms are typically vague and depend on the anatomical location and function of the bowel segment containing the tumor. Later, they generally include pallor, cachexia, ascites, hepatomegaly, and lymphangiectasis.
Cancer on the right side
On the right side of the colon (which absorbs water and electrolytes), early tumor growth causes no signs of obstruction because the tumor tends to grow along the bowel rather than surround the lumen, and the fecal content in this area is normally liquid. It may, however, cause black, tarry stool; anemia; and abdominal aching, pressure, or dull cramps.
As the disease progresses, the patient develops weakness, fatigue, exertional dyspnea, vertigo and, eventually, diarrhea, obstipation, anorexia, weight loss, vomiting, and other signs and symptoms of intestinal obstruction. In addition, a tumor on the right side may be palpable.
Cancer on the left side
On the left side, a tumor causes signs and symptoms of an obstruction even in early stages because in this area, stool is of a formed consistency. It commonly causes rectal bleeding (typically ascribed to hemorrhoids), intermittent abdominal fullness or cramping, and rectal pressure.
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