Overview
The rectum is the lower part of the colon that connects the large bowel to the anus. The rectum's primary function is to store formed stool in preparation for evacuation. Like the colon, the 3 layers of the rectal wall are as follows:
Mucosa, Muscularis propria, Mesorectum
Of the 150,000 cases of colorectal cancer diagnosed each year in the United States, more than 40,000 people are diagnosed with rectal cancer. The most common type of rectal cancer is adenocarinoma, which is a cancer arising from the mucosa. Cancer cells can also spread from the rectum to the lymph nodes on their way to other parts of the body.
Like colon cancer, the prognosis and treatment of rectal cancer depends on how deeply the cancer has invaded the rectal wall and surrounding lymph nodes. However, although the rectum is part of the colon, the location of the rectum in the pelvis poses additional challenges in treatment when compared with colon cancer.
Causes
Rectal cancer usually develops over several years, first growing as a precancerous growth called a polyp. Some polyps have the ability to turn into cancer and begin to grow and penetrate the wall of the rectum.
The actual cause of rectal cancer is unclear. However, the following are risk factors for developing rectal cancer:
- Increasing age
- Smoking
- Family history of colon or rectal cancer
- High-fat diet and/or a diet mostly from animal sources
- Personal or family history of polyps or colorectal cancer
Family history is a factor in determining the risk of rectal cancer. If a family history of colorectal cancer is present in a first-degree relative (a parent or a sibling), then endoscopy of the colon and rectum should begin 10 years before the age of the relative's diagnosis or at age 50 years, whichever comes first.
Symptoms
An often forgotten risk factor, but perhaps the most important, is the lack of screening for rectal cancer. Routine cancer screening of the colon and rectum is the best way to prevent rectal cancer.
- Seeing blood mixed with stool is a sign to seek immediate medical care. Although many people bleed due to hemorrhoids, a doctor should still be notified in the event of rectal bleeding.
- Prolonged rectal bleeding (perhaps in small quantities that is not seen in the stool) may lead to anemia, causing fatigue, shortness of breath, light-headedness, or a fast heartbeat.
- A rectal mass may grow so large that it prevents the normal passage of stool. This blockage may lead to the feeling of severe constipation or pain when having a bowel movement. In addition, abdominal pain or cramping may occur due to the blockage.
- The stool size may appear narrow so that it can be passed around the rectal mass. Therefore, pencil-thin stool may be another sign of an obstruction from rectal cancer.
- A person with rectal cancer may have a sensation that the stool cannot be completely evacuated after a bowel movement.
- Weight loss: Cancer may cause weight loss. Unexplained weight loss (in the absence of dieting or a new exercise program) requires a medical evaluation.
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