Colorectal cancer starts in the large intestine (colon) or the rectum (end of the colon). It usually develops from a polyp that has formed on the lining of the colon. Many cases of colon cancer have no symptoms. Symptoms may include lower abdominal pain, blood in the stool, intestinal obstruction, narrow stools, unexplained anemia, and weight loss.
Risk factors for colorectal cancer include old age, colon diseases for more than eight years, obesity, and some rare inherited disorders. Lifestyle factors like little exercise, drinking a lot of alcohol, and diet high in red or processed meat also increase the risk. Up to 30% of colorectal cancers may be due to genetic factors.
Having a close relative diagnosed at early age increases the risk significantly. Treatment depends partly on the stage of the cancer. When treated at an early stage, most patients survive at least five years after their diagnosis. However, the five-year survival rate drops considerably once the cancer has spread. If the colon cancer does not come back (recur) within five years, it is considered cured.