The terminal part of the large intestine is called the rectum. It functions as a receptacle for stool, and serves to hold and periodically, expel fecal matter through the anal canal. The anal canal, which is about 4 cm long, has a sphincter at the end, which ensures that stool is not expelled involuntarily. Stool is passed out of the body a combination of contraction of the intestinal / rectal wall to propel the stool forward and relaxation of the sphincter to allow the stool to be expelled from the body.
The rectum is 12 cm long and has a top, middle and lower third. Cancer may affect any part of the rectum and may be in the form of an ulcer, a growth or thickening. Patients suffering from rectal cancer may complain of fresh blood in the stool, pain while passing stool, constipation or change in bowel habits. Occasionally, rectal cancer may be detected when the patient is being investigated for anemia.
Patients in whom a rectal cancer is being suspected require a thorough clinical examination; a per rectal examination, in which the doctor will insert a gloved finger into the rectum, is mandatory. This examination helps the doctor to determine where the patient�s rectal growth starts in reference to the external opening of the anus. In addition, per rectal examination allows the doctor to judge whether the tumour is fixed to the deeper tissues or is superficial and confined to the wall of the rectum.
Following the examination, the patient requires to undergo an endoscopic examination called colonoscopy. This involves the insertion of a flexible tube inside the large intestine, to see it from within. Since patients with rectal cancer may have a second lesion elsewhere in the lumen of the large intestine, it is important that the entire length of the large intestine be visualized.
Any abnormality noted is then biopsied. The biopsy specimen is examined by a pathologist to determine whether the patient has cancer. Every growth / ulcer may not necessarily be cancerous.
On confirming cancer, the doctor will prescribe certain tests to determine the extent of disease i.e. the stage of disease. There are three aspects which are assessed, local spread of the tumour, number of lymph nodes involved and the presence of tumour in other organs, such as liver and lung. This is referred to respectively as T, N and M for Tumour, Node and Metastasis.
A surgical operation is necessary when attempting to cure rectal cancer. The operation may be in the form of low anterior resection, in which the natural route for passage of stool remains intact, or in the form of abdomino-perineal resection ( APR), in which the natural passage is removed surgically, and a stoma i.e. opening, is fashioned on the belly. In the latter situation, stool is expelled into a bag. The latter operation is the only possibility in patients with presence of disease close to the opening of the anal canal or with infiltration of the muscle that imparts control over the passage of stool.
Patients with disease that has spread beyond the wells of the rectum, or with evident spread to the lymph glands of the pelvis, or with the possibility of conversion of an abdomino-perineal resection to a surgery that does not require creation of a new passage are recommended concurrent chemo-radiotherapy before surgery.
Concurrent chemo-radiotherapy refers to the administration of chemotherapy along with radiotherapy. The aim of this chemotherapy is to enhance the effect of radiotherapy. This treatment has evolved as a result of a series of trials, in which addition of chemotherapy to radiotherapy was found beneficial. Patients may either receive the chemotherapy in the form of a prolonged intravenous infusion or in the oral form. The latter scores over the former, in view of convenience.
Radiotherapy is the treatment of cancer using ionizing radiation. X-rays are directed to the affected part of the body. The DNA of rapidly dividing cells is destroyed; most cancer cells divide very rapidly, and the damage to their DNA can kill these cells or limit their ability to divide and increase in number. Sophisticated techniques, 3DCRT, IMRT and IGRT, help limit the dose of radiotherapy being received by normal structures in the vicinity of the rectum- the small intestine, the bone marrow on pelvic bones, the urinary bladder, the genitals.
Combined chemo-radiotherapy improves the possibility of undergoing surgery that helps preserve the normal passage of stools in patients thought fit only for APR. In addition, it also reduces the chance of cutting through the tumour during surgery. The treatment lasts for 5 weeks; surgery is performed nearly two months after completion of chemo-radiotherapy, to maximize the chances of preserving the normal anatomy.
