History: Individuals are usually asymptomatic in the early stages of colon cancer, some for up to five years, and often will discover cancer through screening tests. Occasionally, the individual will report no symptoms at all until the tumor grows so large that it causes a bowel obstruction or rupture of the intestine.
However, individuals with colon cancer may report blood in the feces, changed bowel habits (diarrhea or constipation lasting more than a few days), abdominal pain or cramping that radiates toward the middle of the abdomen (umbilicus) or around the anus (perianal), loss of appetite (anorexia), weakness and fatigue, and nausea and/or vomiting. These symptoms tend to vary depending upon the location of the tumor. In general, if the tumor is located in the segment of colon closest to the small intestine (right or ascending colon), individuals often report abdominal pain, nausea, and vomiting. Tumors in the segment of colon that is farthest from the small intestine and closest to the rectum (left or descending colon) are more likely to cause passage of blood or mucus, an alteration in bowel habits, and a feeling that the bowel is not empty after defecation. Regardless of the tumor's location, weakness and fatigue may be reported due to chronic blood loss, and constipation may alternate with increased frequency and loose stools.
A complete history of personal and family illness is usually obtained as an aid in diagnosis.
Physical exam: Examination of the abdomen by touch (palpation) may reveal a colonic mass. Abdominal palpation may also reveal an enlarged liver, which suggests that the cancer has spread from the colon to other nearby organs (metastasized). Digital rectal examination may be done and a stool sample obtained for occult blood determination. Signs of general health status are observed.
Tests: The most important tests for detection of colon cancer are routine screening tests. Screening tests for average-risk individuals over 50 years of age may include a chemical test done annually on a stool sample (fecal occult blood test, or FOBT), flexible sigmoidoscopy every 5 years, double-contrast barium enema every 5 to 10 years, and colonoscopy every 10 years. Double-contrast barium enema is able to detect about 90% of colon tumors (Hassan).
FOBT can identify blood that may be hidden (occult blood) within the fecal material. Diagnostic tests for colon cancer may include an x-ray procedure to visualize the colon (barium enema) or visualization of the entire colon (full colonoscopy) using a flexible fiber-optic viewing instrument (endoscope) that is inserted through the rectum. Flexible sigmoidoscopy can help view the rectum and lower half of the colon, and colonoscopy, which uses a longer (60- to 180-cm) flexible colonoscope, allows visualization of the entire colon. Colonoscopy also allows a small sample of tissue (biopsy) to be taken from the tumor, which can then be examined microscopically to confirm that it is cancerous (histopathological confirmation).
A complete blood count (CBC) can be done to rule out anemia. Additional blood tests, including measurement of a molecule that is associated with cancer cells (carcinoembryonic antigen, or CEA test), a liver enzyme test, and a kidney function test, may indicate the extent of disease spreading (metastasis) from the colon to other organs. A chest x-ray may be used to look for evidence of metastasis into the lungs. The extent of cancer growth (staging) can be determined using harmless, low-energy radio waves (MRI) or computer analysis of x-ray data (CT); a special CT scan staging system includes stages T1 through T4, ranging from intraluminal polypoid mass with no thickening of the bowel wall to gradations of thickening, thickening with invasion outside the intestinal wall, and distant metastases. Positron emission tomography (PET scan) with fluorodeoxyglucose (FDG) is of value in detecting recurrent disease and to visualize colon cancer that may have metastasized. Angiography may be useful to evaluate the potential spread of cancer to the liver and to diagnose metastasis to the liver and other organs. Ultrasound from within the colon (endoluminal ultrasound) can provide important information about how far colorectal cancers have invaded into or through the bowel wall. Ultrasound may also be used to determine if colorectal cancer has metastasized to the liver and other organs.