Rectal cancer

ALSO KNOWN AS: Colorectal cancer

RELATED CONDITIONS: Colon cancer

DEFINITION: The rectum is the last eight inches of the colon (large intestine). Almost all rectal cancers are adenocarcinomas. Adenocarcinomas are cancers that begin in cells that line internal organs of the body, in this case, the lining of the rectum. Since the colon and rectum are continuous, cancer may develop in both places simultaneously. Often, colon and rectal cancer are talked about together as colorectal cancer because their causes and treatments are similar.

Risk factors: Rectal cancer usually develops slowly, so it is much more common in people over fifty. In addition to age, the link between diet and rectal cancer is well established. Rectal cancer is more common in people who eat large amounts of animal fats (such as red meat) and saturated vegetable oils (such as corn oil but not olive or fish oils). For example, individuals in Africa who eat mainly a plant-based diet have low levels of colorectal cancer. Still, when these people move to Western countries and adopt a meat-based diet, their incidence of colorectal cancer rises to the same level as that of other people living in these countries.

Other lifestyle factors that increase the risk of rectal cancer include heavy alcohol use, smoking, obesity, and lack of physical exercise. A family history of colorectal cancer or a history of polyps developing in the colon and rectum, especially at an early age, also increases the risk of rectal cancer. Although risk factors are important screening tools, many people who develop rectal cancer have no specific risk factors.

Etiology and the disease process: Genetics and the environment play a role in the development of rectal cancer. The cells lining the colon and rectum are replaced about every six days. These cells develop in interior tissue layers and work to line the rectum, after which they stop dividing. Cancer develops when these cells continue to divide after reaching the rectal lining. The cells then form tumors that grow into the rectal wall. Researchers have found that cells lining the wall of the rectum must develop at least four genetic defects to become cancerous.

Incidence: The National Cancer Institute estimates that about 46,000 new cases of rectal cancer occur annually. Colorectal cancer deaths account for about 9 percent of deaths in men and 8 percent of cancer deaths in women. Reoccurrence rates range from 3.7 to 50 percent depending on the grade or stage of the tumor, surgery success, and location of the tumor. Cancer in the lower portion of the rectum occurs more often.

Rectal cancer is more common in industrialized countries than in developing nations, though this is likely due to a lack of testing. It affects slightly more men than women and is highest among individuals of Ashkenazi Jewish heritage. Most people diagnosed with colorectal cancer are over age fifty, although people who are genetically predisposed to the disease may develop it in childhood or early adulthood.

Symptoms: Rectal cancer often has few symptoms until the disease becomes advanced. The most common symptoms include changes in bowel activity (constipation or diarrhea), blood in the stool, abdominal pain, a continuous feeling that the rectum is full, and general fatigue.

Screening and diagnosis: Abnormal cells gradually become cancerous over ten to fifteen years, so screening is essential for prevention and early treatment. Individuals with no specific risk factors should begin screening at fifty. In contrast, those with specific risk factors (such as a family history of polyps) should discuss earlier screening with their doctor. A colonoscopy can detect polyps (growths) or abnormalities in the rectal lining. If abnormalities are detected, a biopsy (tissue sample) is taken, and the tissue is examined under the microscope for cancer. An ultrasound of the rectum may also help to determine how far the cancer has spread.

Rectal cancer is evaluated using the stage TNM (tumor/lymph node/metastasis) staging system. Tumors are graded based on their invasiveness, with T1 indicating penetration into the layer below the surface lining and T4 indicating tumor invasion into other organs. Lymph nodes (N) are graded for involvement, with higher numbers indicating greater spread of the disease. Metastasis is evaluated as either absent (M0) or present (M1). Combining this information results in cancer stages designated as I (least advanced) to IV (most advanced).

Treatment and therapy: Treatment depends on the stage of the cancer. Radiation and chemotherapy used in conjunction with surgery decrease the likelihood of recurrence. Radiation may be used before and after surgery. Chemotherapy involves the administration of multiple antineoplastic drugs. Surgery options include transanal endoscopic microsurgery (TEMS), low anterior resection (LAR), and abdominoperineal resection (APR). TEMS is a conservative treatment to remove cancerous cells from the anus. LAR is used in cases of large tumors to remove some or all of the rectum. APR involves the removal of the anus, rectum, and colon, accompanied by a colostomy.

Prognosis, prevention, and outcomes: Survival rates depend on the stage at which cancer is detected, but the overall survival rate for rectal cancer diagnoses is 68 percent. The five-year survival rate for individuals with cancer localized in the rectum is 91 percent. These individuals are diagnosed in the early stages of the disease and receive medical intervention before the cancer can spread. Individuals whose cancer has spread regionally to the lymph nodes near the rectum or the abdominal lining have a 74 percent five-year survival rate. For patients with distant spread cancer in the liver, lungs, or distant lymph nodes, five-year survival rates are around 17 percent.

Bibliography

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