What Is Rectal Cancer?
The rectum is the lower part of the colon that connects the large bowel to the anus. The function of the rectum is to store formed stool in preparation for removal from the body. Like the colon, the three layers of the rectal wall are as follows:
- Mucosa: This layer of the rectal wall lines the inner surface. The mucosa is composed of glands that secrete mucus to help the free passage of feces from the body.
- Muscularis propria: This middle layer of the rectal wall is made of muscles that aid the rectum keep its shape and contract in a synchronized fashion to expel stool.
- Mesorectum: This is a fatty tissue that surrounds the rectum.
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In addition to these three layers, another important component of the rectum is the surrounding lymph nodes which are part of the immune system and help in conducting scrutiny for harmful materials, bacteria, and viruses that may be threatening the body. Lymph nodes surrounds every organ in the body, including the rectum.
The prognosis and treatment of rectal cancer depends on how deeply the cancer has attacked 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 of Rectal Cancer
Rectal cancer usually grows over several years, first growing as a precancerous growth called a polyp. Some polyps have the ability to turn into cancer and start to grow and enter the wall of the rectum. The actual cause of rectal cancer is uncertain. The following are risk factors for developing rectal cancer:
- Increasing age
- Family history of colon or rectal cancer
- Inflammatory bowel disease (IBS)
- High-fat diet and/or a diet mostly from animal sources
- Family history of polyps or colorectal cancer
Symptoms of Rectal Cancer
Rectal cancer can cause many signs and symptoms that require a person to seek medical help. However, rectal cancer may also be present without any symptoms. Symptoms and signs to be aware of include the following:
- Rectal bleeding
- Blood mixed with stool
- Change in bowel habits
- Prolonged rectal bleeding (perhaps in small quantities that is not seen in the stool) may lead to anemia, lightheadedness, fatigue, fast heartbeat.
- Bowel obstruction
- A rectal mass may grow so large that it prevents the normal passage of stool.
- The stool size may appear narrow so that it can be passed around the rectal mass. Therefore, pencil-thin or narrow stools 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.
- Unexplained weight loss
Sometimes hemorrhoids or pile (swollen veins in the anal area), can mimic the pain, discomfort, and bleeding seen with anal-rectal cancers. Individuals who have the above symptoms should get a medical exam of their anal-rectal area to be certain they have an precise diagnosis.
Diagnosis of Rectal Cancer
The only way to prevent this disease is proper colorectal screening leading to the detection and removal of precancerous growths. Screening tests for rectal cancer include the following:
- Fecal occult blood test (FOBT) or fecal immunochemical tests (FIT): Early rectal cancer may damage blood vessels of the rectal lining and cause small amounts of blood to leak into the feces. The stool appearance may not change. The fecal occult blood test requires placing a small amount of stool on a special paper that is provided by a doctor. The doctor then applies a chemical to that paper to see if blood is present in the stool sample.
- Endoscopy: This involves a doctor inserting a flexible tube with a camera at the end called an endoscope, through the anus and into the rectum and colon. During this procedure, the doctor can see and remove abnormalities on the inner lining of the colon and rectum.
If rectal cancer is suspected, the tumor can be detected physically through either digital rectal examination (DRE) or endoscopy.
- Not all rectal cancers can be detected this way. A digital rectal examination is performed using a lubricated gloved finger inserted through the anus by the doctor, to feel the cancer on the rectal wall. Detection is dependent on how far the tumor is from the anus. If an irregularity is detected by a digital rectal examination, then an endoscopy is performed for further check of the cancer.
- Flexible sigmoidoscopy involves the insertion of an endoscope through the anus and into the rectum.
- Rigid sigmoidoscopy is the insertion of a rigid optical scope inserted through the anus and into the rectum. Rigid sigmoidoscopy is typically performed by either a gastroenterologist or a surgeon. The advantage of rigid sigmoidoscopy is that a more exact measurement of the tumor’s distance from the anus can be gotten, which may be important if surgery is required.
- A colonoscopy may be performed. For a colonoscopy, an endoscope is inserted through the anus and into the rectum and colon.
Stages of Rectal Cancer
The treatment and prognosis of rectal cancer depend on the stage of the cancer, which is determined by the following three reflections:
- How deeply the tumor has attacked the wall of the rectum
- Whether there is presence of cancer in the lymph nodes
- Whether the cancer has spread to any other locations in the body
Rectal cancer mostly spread to the liver and the lungs. There are several ways to stage rectal cancer; Duke’s classification, and the TNM classification (TNM represents T, the location of the tumor; N, the nodes [lymph nodes] invaded by tumor cells, and M, metastasis of tumor cells to other organs. The TNM classification is very detailed; many doctors choose to use the more simplified I-IV stages. The stages of rectal cancer are as follows:
- Stage I: The tumor involves only the first or second layer of the rectal wall, and no lymph nodes are involved.
- Stage II: The tumor penetrates into the mesorectum, but no lymph nodes are involved.
- Stage III: Regardless of how deeply the tumor penetrates, the lymph nodes are involved with the cancer (this stage can be divided into IIIa, IIIb, and IIIc, depending how far the cancer has grown through rectal tissue or through its wall).
- Stage IV: Convincing evidence of the cancer exists in other parts of the body, outside of the rectal area.
Localized rectal cancer includes stages I-III. Metastatic rectal cancer is stage IV. The goals of treating localized rectal cancer are to ensure the removal of all the cancer and to prevent a recurrence of the cancer, either near the rectum or elsewhere in the body.
Medical Treatments for Rectal Cancer
Surgery is likely to be the only necessary step in treatment if stage I rectal cancer is diagnosed.
The risk of the cancer coming back after surgery is low, and therefore, chemotherapy is not usually recommended. Sometimes, after the removal of a tumor, the doctor discovers that the tumor penetrated into the mesorectum (stage II) or that the lymph nodes contained cancer cells (stage III). In these individuals, chemotherapy and radiation therapy are offered after recovery from the surgery to reduce the chance of the cancer returning. Chemotherapy and radiation therapy given after surgery is called adjuvant therapy.
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Medications Treatment of Rectal Cancer
The following chemotherapy drugs may be used at various points during therapy:
- 5-Fluororacil (5-FU): This drug is given intravenously either as a continuous infusion using a medication pump or as quick injections on a routine schedule. Side effects may include diarrhea, fatigue, mouth sores, and hand, foot, and mouth syndrome.
- Capecitabine (xeloda): This drug is given orally and is converted by the body to a compound similar to 5-FU. Capecitabine has similar effects on cancer cells as 5-FU and can be used either alone or in combination with radiation therapy. Side effects are similar to intravenous 5-FU.
- Leucovorin (Wellcovorin): This drug increases the effects of 5-FU and is usually administered just prior to 5-FU administration.
- Oxaliplatin (Eloxatin): This drug is given intravenously once every two or three weeks. Oxaliplatin has recently become the most common drug to use in combination with 5-FU for the treatment of metastatic rectal cancer. Side effects include fatigue, increased risk of infection, nausea, anemia, and tingling or numbness of the fingers and toes.
- Irinotecan (Camptosar, CPT-11): This drug is given intravenously once every one to two weeks. Irinotecan is also commonly combined with 5-FU. Side effects include fatigue, diarrhea, increased risk of infection, and anemia. Because both irinotecan and 5-FU cause diarrhea, this symptom can be severe and should be reported immediately to a doctor.