Overview of Rectal Cancer
The rectum is part of the digestive tract. It is comprised of the last 6–8 inches (15–20 centimeters) of the large colon. Cancer that originates in the colon or rectum may be called rectal cancer, colon cancer, or colorectal cancer. Because treatment and progression of colon cancer and rectal cancer may be different, they are often reported separately.
Anatomy of the Rectum
The rectum is approximately 15 centimeters (6 inches) in length. For the purpose of treatment, the organ often is divided into three segments—the lower, middle, and upper sections. Anatomically these segments correspond to (measuring from the anal verge) the first 7–10 centimeters; the next 4–5 centimeters, and the last 4–5 centimeters.
Physiologically, there are two muscular mechanisms involved in maintaining fecal continence. The internal and external sphincter muscles control the anal canal lumen and the puborectalis sling system leads to enhanced continence despite sneezing or coughing.
Screening for Rectal Cancer
Tests used to help detect cancer at an early stage and help improve the outcome are called screening tests. Colorectal cancer screening tests include digital rectal examination (DRE), proctoscopy, colonoscopy, and stool occult blood testing. Beginning at the age of 50, a colonoscopy and annual DRE and occult blood testing should be performed. Younger patients who should undergo colorectal cancer screening include those under the age of 50 with a family history of colon cancer, and patients with a history of rectal or gynecologic cancer or ulcerative colitis.
Rectal Cancer Diagnosis
In general, rectal and rectosigmoid cancer (i.e., cancer that originates in the rectum and sigmoid colon) are more likely than other colon cancers to produce symptoms prior to diagnosis. These cancers often cause bleeding that can be observed. Other signs and symptoms include a change in bowel activity, unexplained constipation or a reduction in stool caliber, urgency, and inadequate emptying of the bowels. With advanced tumors, urinary symptoms or buttock pain may occur. These symptoms usually lead to an evaluation of the colorectal area.
Digital rectal examination (DRE) may be used as an initial screening examination; however, tumors located more than 7 centimeters from the anal verge may be missed during this examination. Additional studies include barium enema, usually with flexible sigmoidoscopy and/or colonoscopy used as a complementary procedure.
If a tumor is discovered by any of the above procedures, a biopsy (removal of a tissue sample for microscopic evaluation) should be performed. Pathologically, adenocarcinoma (cancer that originates in the lining of the colon) accounts for 90 to 95% of large bowel cancers. Other tumor types include squamous cell cancers, carcinoid tumors, adenosquamous carcinomas, and undifferentiated tumors.
Rectal Cancer Staging
Once a diagnosis of rectal cancer has been confirmed, staging procedures are performed. These include computed tomography scan (CT scan) of the chest, abdomen, and pelvis; complete blood count (CBC); liver and kidney function tests; urine analysis; and measurement of the tumor marker CEA (carcinoembryonic antigen).
The goal of staging is to determine the extent and location of the tumor to develop appropriate treatment strategies and estimate a prognosis.
The staging for rectal cancer closely approximates the staging for colon cancer. Originally, there was the Duke's classification system, which placed the cancer into one of three categories (Stages A, B, C). This system was subsequently modified by Astler-Coller to include a fourth stage (Stage D), and was modified again in 1978 by Gunderson & Sosin.
More recently, the American Joint Committee on Cancer (AJCC) has introduced the TNM staging system, which places the cancer into one of four stages (Stages I-IV). Listed below are the Duke and TNM staging systems.
Modified Duke Staging System for Rectal Cancer
Modified Duke A: Tumor penetrates into the mucosa of the bowel wall, but no further
Modified Duke B:
- B1:Tumor penetrates into, but not through the muscularis propria (the muscular layer) of the bowel wall
- B2: Tumor penetrates into and through the muscularis propria of the bowel wall
Modified Duke C:
- C1: Tumor penetrates into, but not through the muscularis propria of the bowel wall; there is pathologic evidence of colon cancer in the lymph nodes
- C2: Tumor penetrates into and through the muscularis propria of the bowel wall; there is pathologic evidence of colon cancer in the lymph nodes
Modified Duke D: Tumor has spread through the lymph nodes to organs such as the liver, lung, or bone.
TNM Staging System for Rectal Cancer
- T1: Tumor invades submucosa
- T2: Tumor invades muscularis propria
- T3: Tumor invades through the muscularis propria into the subserosa, or into the perirectal tissues
- T4: Tumor directly invades other organs or structures, and/or perforates
- N0: No regional lymph node metastasis
- N1: Metastasis in 1 to 3 regional lymph nodes
- N2: Metastasis in 4 or more regional lymph nodes
- M0: No distant metastasis
- M1: Distant metastasis present
Rectal Cancer Stage Groupings
- Stage 1 - T1 N0 M0; T2 N0 M0
- Stage 2 - T3 N0 M0; T4 N0 M0
- Stage 3 - any T, N1-2, M0
- Stage 4 - any T, any N, M1
Questions to Ask Your Doctor about Colon Cancer (Free Handout)