Rectal cancer refers to the uncontrolled growth of the cells in the rectum which is the last part of the large bowel close to the anus. Rectal cancer may occur in isolation or along with cancer of the colon (the longest part of the large bowel). Rectal and colon cancer are together called colorectal cancer. The rectum is around six-inch long. It serves the purpose of storing the stools until a person has bowel movements. Rectal cancer may develop gradually over several years. It usually starts as a small growth or mass, called a rectal polyp, confined to the inner lining of the rectum. Some of the rectal polyps when left untreated may grow into rectal cancer. Untreated rectal cancer can spread over time to involve other organs, particularly the liver and lungs.
Staging of rectal cancer means determining the extent to which it has developed by growing and spreading to near and distant sites. Staging is important because it helps plan cancer management besides knowing what the disease outlook and prognosis will be like. Thus, after diagnosing rectal cancer, doctors explore whether the cancer is limited to its site of origin or spread to nearby or distant sites. Staging is done through a combination of clinical assessment, imaging studies (such as computed tomography [CT] scan, X-ray, ultrasound, magnetic resonance imaging [MRI] scan and positron emission tomography [PET] scan) and colonoscopy (a procedure to look inside the rectum and colon for any abnormal areas or growths).
The staging system most often used for colorectal cancer is the TNM system of the American Joint Committee on Cancer (AJCC). The system depends on
- The extent (size) of the tumor (T).
- The spread to the nearby lymph nodes (N).
- The spread (metastasis) to distant sites (M).
Various combinations of TNM intensity help the surgeon classify the tumor.
Rectal cancer is divided into five stages.
- Stage 0: This stage is also called rectal carcinoma in situ, which means that the cancerous cells are limited to the mucosa (innermost layer) of the wall of the rectum. Cancer may appear as a polyp (growth) that just about projects from the mucosa into the lumen of the rectum. These cancerous cells, however, have the potential of spreading to the deeper layers of the rectum. Thus, treatment at this stage is expected to give the best outlook for the patient. Cancer may be removed at this stage by surgery such as local excision, a polypectomy or polyp removal surgery. More extensive surgeries may be needed in cases where the growth is large.
- Stage I: In this stage, the cancerous cells have spread into the deeper layers of the rectal wall beyond the mucosa. Cancer may have spread up to the submucosa (the tissue layer under the mucosa) or the muscle layer of the rectal wall. Surgery is generally done for the treatment at this stage. If the cancer is extensive or not completely removable by surgery, chemotherapy or radiation may also be given. Chemotherapy and radiation are also given as the mainstay of treatment in patients who are unfit for surgery or have poor general health.
- Stage II: This stage is further divided into three substages.
- Stage IIA: Rectal cancer has spread beyond the muscle layer to involve the outermost layer or serosa of the rectal wall.
- Stage IIB: In this stage, cancer invades the serosa to involve the visceral peritoneum (the tissue lining the abdominal organs).
- Stage IIC: Cancer has crossed the serosa to invade the nearby organs.
Different combinations including chemotherapy, radiation and surgery are generally considered at this stage.
4. Stage III: In this stage, cancer has further advanced to invade the lymph nodes in the pelvic area. It is further divided into stages IIIA, IIIB and IIIC depending upon the extent of lymph node involvement. A combination of surgery, radiation and chemotherapy prioritized according to the patient’s needs is considered at this stage.
5. Stage IV: It is the most advanced stage where cancer spreads to different distant organs (such as the liver, lungs and ovaries) and distant lymph nodes. Depending upon how extensive the spread is, this stage is further divided into stages IVA, IVB and IVC. A combination of surgery, radiation and chemotherapy prioritized according to the patient’s needs is considered at this stage. The focus is to improve the quality of life of the patient.
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