A Dukes A colon cancer is confined to the muscular lining of the intestinal wall. A Dukes B cancer is one in which the cancer has grown beyond the muscular layer of the bowel wall, and a Dukes C colon cancer has spread to involve the lymph nodes.
The TNM classification classifies colon cancers in a more precise fashion. "T" represents tumor and a cancer is placed in one of seven groups depending on the depth of cancer invasion into the bowel wall. "N" stands for lymph node and a tumor is given a "N" ranking according to whether the cancer has spread to the lymph nodes and how many lymph nodes that are involved. The "M" relates to whether there is cancer spread to other organs distant from the colon and lymph nodes. Once a particular colon cancer is given a TNM classification it can then be staged.
Generally, a stage I cancer is one in which the tumor is confined to the bowel wall, similar to a Dukes A lesion. A stage II cancer is one in which the cancer has grown beyond the muscular layer of the bowel wall similar to a Dukes B lesion. A stage III colon cancer is one in which there has been spread to lymph nodes which would generally correlate with a Dukes C cancer. A stage IV colon cancer is one in which there is spread to distant organs.
Staging of colon cancers is useful in predicting the probability of the cancer recurring after surgical removal. It also helps in determining whether chemotherapy may be helpful in preventing or decreasing the likelihood of a cancer recurrence. Stage I cancers have a survival rate of 80-95 percent. Stage II tumors have survival rates ranging from 55 to 80 percent. A stage III colon cancer has about a 40 percent chance of cure and a patient with a stage IV tumor has only a 10 percent chance of a cure.
Chemotherapy is used after surgery in many colon cancers which are stage II, III, and IV as it has been shown that it increases the survival rates. This is not the case in stage I cancers, and therefore chemotherapy is rarely used in this setting. The vast majority of stage I cancers are cured with surgery alone.
Carcinoembryonic antigen or CEA is a protein which can be measured in the blood. In many colon cancers the CEA level is elevated. 50 percent of patients with stage II and III cancers have elevated CEA levels. After surgery, with a curative resection of the cancer the CEA should return to normal in one to four months.
After surgery, the CEA level can be periodically monitored. If the levels begin to rise above 6.0 ng/ml there is a high correlation of recurrence of the cancer. This is not an absolute, as other conditions can elevate the CEA level, including diverticulitis, pancreatitis, peptic ulcer disease, hepatitis, and smoking. If these other causes are excluded then one must look for recurrence of the cancer. Often this involves CAT scans of the abdomen. Many times the cancer has recurred in the liver. If there are relatively few lesions in the liver, a patient may be a candidate for removing these recurrent tumors. In most cases, there are so many lesions in the liver it makes their removal impossible.
In some cases the CEA may be rising, but the scans do not show a recurrent cancer. In this setting it is sometimes appropriate to reoperate and look inside the abdomen in hopes of finding a localized recurrent cancer which can be removed. It is not entirely clear yet whether this therapeutic approach actually increases survival. Further studies are needed to clarify this issue.
Colon cancer is a curable cancer if found early, and especially if it is diagnosed in a precancerous state such as a polyp. Although surgery and chemotherapy have improved cure rates for colon cancer, it should be the goal of physicians and patients to diagnose colon lesions before they become malignant. Therefore, yearly physical examinations, checking the stool for occult blood, sigmoidoscopy and colonoscopy are our best tools in preventing colon cancer.
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Last Editorial Review: 9/6/2001 6:40:00 AM