A colonoscopy is a widely recognized procedure for examining parts of the digestive system. Understanding what it evaluates clarifies its role in detecting various conditions, including different types of cancer.
What a Colonoscopy Examines
A colonoscopy examines the inner lining of the large intestine, including the colon and rectum. A flexible tube with a camera, known as a colonoscope, is inserted through the anus and advanced through the entire colon. Its main purpose is to identify and remove precancerous polyps and detect colorectal cancer. It also allows for visual inspection of the colon’s interior, enabling doctors to spot abnormalities like inflammation, ulcers, or diverticula. While the colonoscope passes through the rectum and anal canal, it is not specifically designed to comprehensively examine the anal canal or perianal region for anal cancer. Its focus remains on the larger bowel segments.
Understanding Anal Cancer
Anal cancer develops in the tissues or lining of the anal canal. The anal canal is a short tube (1.5 to 2 inches long) at the end of the rectum, through which stool exits the body. It is distinct from colorectal cancer, which originates in the colon or rectum. Though both are in the lower digestive tract, they differ in cellular origin and biological behavior. Most anal cancers (nearly 9 out of 10 cases) are squamous cell carcinomas, arising from the squamous cells lining the anal canal.
Screening and Detection for Anal Cancer
Unlike colorectal cancer, there is no universally recommended population-wide screening program for anal cancer for the general public. Instead, detection relies on specific examinations and targeted screening for high-risk individuals.
A digital rectal exam (DRE) involves a healthcare provider feeling for lumps or abnormal areas in the anal canal and distal rectum. This simple procedure can detect abnormalities larger than 0.3 cm. An anoscopy involves inserting a small, lighted tube (anoscope) to visualize the anal canal and rectum. High-resolution anoscopy (HRA) uses a magnifying scope to identify subtle cellular changes.
If suspicious areas are found during a DRE or anoscopy, a biopsy (tissue sample) confirms the diagnosis. Targeted screening, including DREs and anal Pap tests, is recommended for high-risk groups like individuals with HIV, those who are HPV-positive, or those with a history of anal warts.
Recognizing Anal Cancer Risk Factors and Symptoms
The most significant risk factor is human papillomavirus (HPV) infection, linked to about 90% of cases. Other risk factors include:
Human immunodeficiency virus (HIV) infection, which weakens the immune system.
A weakened immune system from other causes (e.g., organ transplantation).
Smoking.
Receptive anal intercourse.
Multiple sexual partners (due to increased HPV exposure).
Recognizing anal cancer symptoms is important for early detection, though many can also be caused by less serious conditions like hemorrhoids. Common symptoms include:
Bleeding from the anus or rectum (often minor).
Pain or pressure in the anal area.
A lump or mass near the anus.
Persistent anal itching.
Changes in bowel habits (e.g., stool consistency or shape).
Abnormal discharge from the anus.
Consult a healthcare provider if any of these symptoms are present and persist.