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 rectum has 3 layers of the rectal wall which 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 passage of stool
- Muscularis Propria: This middle layer of the rectal wall is composed of muscles that help the rectum keep its shape and contract in a coordinated fashion to expel stool
- Mesorectum: This fatty tissue surrounds the rectum
The most common type of Rectal Cancer is Adenocarcinoma, 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.
- Rectal cancer can cause many symptoms that require a person to seek medical care. However, rectal cancer may also be present without any symptoms, underscoring the importance of routine health screening. Symptoms to be aware of include the following:
- Bleeding: Blood mixed with stool, is a sign to seek immediate medical care
- Obstruction: 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: Unexpected weight loss
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 not very clear. However, the following are risk factors for developing rectal cancer:
- Increasing age
- Family history of colon or rectal cancer
- High-fat diet or a diet mostly from animal sources
- Personal or family history of polyps or colorectal cancer
An often forgotten risk factor is the lack of screening for rectal cancer. Routine cancer screening of the colon and rectum is the best way to prevent rectal cancer.
Once the patient visits the specialist with the symptoms, in order to determine if the person is suffering from rectal cancer, the following screening tests for rectal cancer are conducted:
- Fecal occult blood test: 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: During endoscopy, a doctor inserts a flexible tube with a camera at the end 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 physically detected through either digital rectal examination. A digital rectal examination is performed by a doctor using a lubricated gloved finger inserted through the anus to feel the cancer on the rectal wall. Not all rectal cancers can be felt this way, and detection is dependent on how far the tumor is from the anus. If an abnormality is detected by a digital rectal examination, then an endoscopy is performed for further evaluation of the cancer.
- A colonoscopy may be performed. In this a flexible endoscope is inserted through the anus and into the rectum and colon. A colonoscopy allows a doctor to see abnormalities in the entire colon, including the rectum.
- A chest x-ray and a CT scan of the abdomen and pelvis are also performed to see whether the cancer has spread further than the rectum or surrounding lymph nodes.
Routine blood studies are performed to assess how a person might tolerate the upcoming treatment.
- In addition, a blood test called CEA (carcinoembryonic antigen) is obtained. The CEA is often produced by colorectal cancers and can be a useful gauge of how the treatment is working. After the treatment, the doctor may regularly check the CEA level as one indicator of whether the cancer has returned. However, checking the CEA level is not an absolute test for colorectal cancers, and other conditions may cause a rise in the CEA level. Likewise, a normal CEA level is not a guarantee that the cancer is no longer present.
The treatment of rectal cancer depends on the stage of the cancer, which is determined by the following 3 considerations:
- How deep has the tumor has invaded the wall of the rectum
- Whether the lymph nodes appear to have cancer in them
- Whether the cancer has spread to any other locations in the body
If the patient is diagnosed with Stage I rectal cancer then surgery is the only necessary step in treatment. The risk of the cancer coming back after surgery is low, and, therefore, chemotherapy is not usually advised.
Sometimes, after the removal of a tumor, the doctor may discover that the tumor has penetrated into the mesorectum which is classified as Stage II or if the lymph nodes contain cancer cells it is considered as the stage III. In these cases, 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 chemotherapy.
If the initial exams and tests show a person to have Stage II or Stage III rectal cancer, then chemotherapy and radiation therapy should be considered before surgery. Chemotherapy and radiation given before surgery is called neoadjuvant chemotherapy. This therapy lasts approximately 6 weeks. Neoadjuvant therapy is performed to shrink the tumor so it can be more completely removed by surgery. In addition, a person is likely to tolerate the side effects of combined chemotherapy and radiation therapy better if this therapy is administered before surgery rather than afterward.
If the rectal cancer is metastatic, then surgery and radiation therapy would only be performed if persistent bleeding or bowel obstructions from the rectal mass exist. Otherwise, chemotherapy alone is the standard treatment of metastatic rectal cancer. At this time, metastatic rectal cancer is not curable. However, average survival times for people with metastatic rectal cancer have lengthened over the past several years because of the introduction of new medications.