Adenocarcinoma of the colon and rectum grows slowly. A long time may pass before it becomes large enough to cause symptoms.
Routine exams are important for early diagnosis.
When symptoms do occur, they vary depending on the location of the tumor, its type, how far it has spread and complications it may have caused.
On the right-hand side of the colon, blockage usually doesn't occur until later stages. This is because the space inside the colon is large, the colon wall is fairly thin and the material passing through is mostly liquid. Some tumors may grow big enough to be felt from the outside of the body. If there is bleeding inside, it usually isn't obvious. However, a person may feel weak or tired because of severe anemia caused by loss of blood.
On the left-hand side of the colon, the space inside the colon is smaller and the material that passes through it is semi-solid. Colon cancer can cause both constipation and diarrhea. A person may feel cramp-like pain in the stomach. The stool may be streaked or mixed with blood.
In rectal cancer, the most common symptom is usually bleeding when going to the bathroom.
Cancer of the rectum should be considered whenever there is rectal bleeding, even if other causes such as hemorrhoids are present. A person may feel as if there is incomplete evacuation. There usually is no pain until later stages of the condition.
Symptoms of advanced disease include:
- A feeling of being full very quickly while eating
- Weakness and pain in the abdominal area
Causes and Risk Factors
There is no single cause of intestinal cancer. Several risk factors may play a role in its development.
Persons between the ages of 40 and 75 are at greater risk of getting colorectal cancer than younger people. More women get colon cancer. More men get rectal cancer.
Conditions such as familial polyposis, Lynch syndrome, Crohn's disease or ulcerative colitis (ulcers in the lining of the large intestines) tend to increase the risk for the disease. Brothers, sisters and children of those already diagnosed with colorectal cancer have a greater chance of getting the disease later in life.
Population groups who have a high rate of colorectal cancer tend to eat low-fiber diets high in animal protein, fat and refined carbohydrates. The exact way the condition occurs is not yet known.