Colorectal cancer begins in either the colon or the
rectum. Both are part of the digestive tract,
sometimes called the GI (gastrointestinal) tract.
This is where food is processed to create energy
and rid the body of waste matter.
The colon has four sections: the ascending colon,
the transverse colon, the descending colon and the
sigmoid colon. Cancer can start in any of the four
sections or in the rectum. Since colon cancer and
rectal cancer
have many features in common, they are often discussed
together.
Before a true cancer develops, there are often earlier
changes in the lining of the colon or rectum. One
type of change is a growth of tissue called a polyp.
Removing the polyp early may prevent it from becoming
cancer.
Over 95% of colon and rectal (colorectal) cancers
are adenocarcinomas. These are cancers of the cells
that line the inside of the colon and rectum. There
are also other types of tumors of the colon and rectum
that are somewhat rare.
The death rate from colorectal cancer has been going
down for the past 20 years. This may be because fewer
people are developing it, more of the cases are found
early or because treatments have improved.
Source: American Cancer Society
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