Cancer of the rectum and the large intestine (colon) are often clubbed under ‘colorectal’ cancer. The rectum is the last part of the large intestine, and begins where the last part of the large intestine ends as a narrow passage to the anus, the final anatomical region where solid waste matter exits the body.
Although, cancer of the rectum and colon may be similar, the treatments are different. The rectum is close to many other organs that occupy an enclosed small space in the pelvis, and hence, rectal cancer can be quite challenging to treat. In the past, the mortality rate was quite high, but with recent developments long-term survival is good, and in many cases, curable.
There is a 30–50% higher incidence of rectal cancer in males than in women. Rectal cancer is slow to develop and can take years to become symptomatic. Although the actual cause is not known, risk factors include increasing age (over 50), a family history of the disease, and a high-fat diet including more of red meat consumption, rather than vegetables.
The incidence has also been observed in persons with excessive body weight, a history of polyps, inflammatory bowel disease or colon cancer itself, radiation therapy with orthovolatage techniques prior to 1950s to the pelvic area for a previous cancer.
Common symptoms include a change in bowel habits, such as diarrhea, constipation or more-frequent bowel movements, dark or red blood, with or without mucus in the stools, narrow stools and painful bowel movement, a feeling of incomplete bowel movement, abdominal pain, anemia, weight loss, and fatigue.
The diagnosis is confirmed by procto-sigmoidoscopy & colonoscopy, which is direct visualization of the tumor through a flexible tube with lighting and a video camera. Colonoscopy over the age of 50, as a routine screening procedure can visualize early cancer, especially when no symptoms are present. Routine blood investigations and a specialized test called CEA (carcinoembryonic antigen), which is higher in persons with colorectal cancers are important markers that are monitored during treatments also. Imaging including CT, MRI or PET-CT scans can assess any spread to other organs.
Staging of rectal cancer involves 5 stages:
- Stage 0. Cancer cells are present on the surface of the rectal lining (mucosa), sometimes within a polyp
- Stage I. Tumor may have penetrated into the rectal wall from the mucosa
- Stage II. Tumor has grown to tissues near the rectum
- Stage III. Tumor spreads to lymph nodes near the rectum, as well as structures and tissues outside the rectal wall
- Stage IV. Tumor spreads to a distant organ or lymph nodes far off from the rectum
Early stages (0 and early 1) are treated by surgical excision, and the later stages involve more complex surgeries.
Standard treatment for stages II and III rectal cancers is typically a combination of chemotherapy and radiation (chemo radiotherapy, CRT) given before surgery (preoperative); large stage 1 rectal cancers can also be treated in a similar manner. CRT can shrink and kill tumor cells, and reduce the risk for recurrence, and also used after surgery (postoperative). Radiation therapy (RT) alone has also been considered in the treatment of rectal cancer, especially in recurrent tumors treated earlier by surgery alone. Oncosurgeons in association with the oncoradiologists can decide if a short-course RT alone may be equivalent to long-course CRT for better survival outcome on an individual case basis. Routine follow-up, as advised, is mandatory in rectal cancer.
CRT, especially for low lying rectal cancers (within 5 cms from anal verge) can help shrink the cancer such that about one third patients can have normal passage after surgery and may not need a colostomy.