Viewer Question
My family member
has been diagnosed as having class C or stage III colon cancer. What does it
mean? How is it related to long term survival?
Doctor's
Answer
Colon cancer can be staged by
several methods. The two most common methods are the TNM classification and
Dukes staging. Dukes classification divides colon and rectal cancer into three
stages, A, B and C. Colon cancers originate from the inner lining of the colon,
called the mucosa. As the cancer grows, it grows larger in the lumen of the
colon, but also grows outward through the other layers which compose the wall of
the colon. It can grow completely through the wall of the colon and invade other
structures and it can spread to lymph nodes. Colon cancer can also spread to
other organs such as the liver.
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.
Thank you for your question.
Last Editorial Review: 9/6/2001 6:40:00 AM
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