Why is colon cancer so frequently fatal? Have doctors made any recent progress in treatments and cures?

R.H.V.

The outlook for people with colon cancer varies greatly depending on how advanced the cancer is when detected. The five-year survival rates are more than 90 percent for early disease localized to the inner portion of the colon wall, 80 percent if the cancer has invaded the muscle layer of the colon wall, 40-60 percent if lymph nodes are involved, and less than 10 percent if other organs (such as the liver or lungs) are involved.

Colon cancer almost always begins in a colon polyp. The cancer grows slowly in the polyp and invades the wall of the colon, advancing to adjacent structures in the abdomen, including lymph nodes. Finally, more distant organs become involved. Colon cancer is generally curable by surgery if it is localized to the bowel. Once it has invaded beyond the colon and into lymph nodes or adjacent structures, surgery alone will not suffice and chemotherapy must be used.

The chemotherapy regimens for colon cancer are not as effective as those for other types of tumors, and research is being done to improve the types of medications available to treat this disease. However, treatment advances over the past decade have included a combined chemotherapy regimen for disease involving lymph nodes (which has raised survival rates from 40 percent to 60 percent), and surgical removal of liver metastases in certain patients (raising survival rates from less than 10 percent to more than 25 percent in those patients).

Without a doubt, the best therapy for colon cancer is early detection. However, the problem with detecting colon cancer is that patients often experience no symptoms in the disease's earliest stages. When the disease advances, patients may report blood in the stool, weight loss, abdominal pain or other symptoms related to obstruction of the colon.

Because most colon cancer arises in polyps and because polyp removal reduces death rates from colon cancer, the current recommendation is to have sigmoidoscopic or colonoscopic screening to detect polyps beginning at age 50 (earlier if one has a family history of colon cancer). Also recommended is a yearly test for hidden blood in the stool (called a fecal occult blood test) to detect the slow bleeding that can be a sign of colon cancer. A positive fecal occult blood test is followed by a colonoscopy to look for the source of bleeding.