Colorectal Cancer
The second most common visceral neoplasm in the United States and Europe, colorectal cancer is nearly equally distributed between males and females. Ninety percent of cases occur in persons older than age 50.
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. Unless the tumor has metastasized, the 5-year survival rate is relatively high: about 80% for rectal cancer and more than 85% for colon cancer. If untreated, the disease is invariably fatal.
Causes
Most colorectal cancers arise from malignant changes in an adenomatous polyp. Age, personal history of neoplasia, and family history increase the risk of colorectal cancer. However, 75% of new cases occur in people without known predisposing factors. An autosomal dominant condition increases risk of a number of cancers, including colorectal cancer. Genetic testing might be indicated for selected patients and relatives.
Other risk factors for colorectal cancer include diseases of the digestive tract, a history of ulcerative colitis (in which case cancer usually starts in 7 to 10 years), and familial polyposis (cancer almost always develops by age 50).
Complications
As the tumor grows and encroaches on the abdominal organs, abdominal distention and intestinal obstruction occur. Anemia may develop if rectal bleeding isn’t treated.
Assessment
Signs and symptoms depend on the tumor’s location. If it develops on the colon’s right side, the patient probably won’t have signs and symptoms in the early stages because the stool is still in liquid form in that part of the colon. He may have a history of black, tarry stools, however, and report anemia, abdominal aching, pressure, and dull cramps. As the disease progresses, he may complain of weakness, diarrhea, constipation, anorexia, weight loss, and vomiting.
A tumor on the left side of the colon causes symptoms of obstruction even in the early disease stages because stools are more completely formed when they reach this part of the colon. The patient may report rectal bleeding (often ascribed to hemorrhoids), intermittent abdominal fullness or cramping, and rectal pressure.
As the disease progresses, constipation, diarrhea, or ribbon- or pencil-shaped stools may develop. The patient may note that the passage of flatus or stool relieves his pain. He may also report obvious bleeding during defecation, dark or bright red blood in the feces, and mucus in or on the stools.
A patient with a rectal tumor may report a change in bowel habits, often beginning with an urgent need to defecate on arising (“morning diarrhea”) or constipation alternating with diarrhea. He also may notice blood or mucus in the stools and complain of a sense of incomplete evacuation. Late in the disease, he may
complain of pain that begins as a feeling of rectal fullness and progresses to a dull, sometimes constant ache confined to the rectum or sacral region.
complain of pain that begins as a feeling of rectal fullness and progresses to a dull, sometimes constant ache confined to the rectum or sacral region.
Inspection of the abdomen may reveal distention or visible masses. Abdominal veins may appear enlarged and visible from portal obstruction. You may note abnormal bowel sounds on abdominal auscultation. Palpation may reveal abdominal masses. Right-side tumors usually feel bulky; tumors of the transverse portion are more easily detected. The inguinal and supraclavicular nodes may also feel enlarged.
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.
Flexible sigmoidoscopy permits visualization of the lower GI tract. It can detect up to 60% 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.
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. Blood studies can detect anemia; liver function tests may suggest metastasis.
Laparoscopic surgery
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