Anal canal cancer is an infrequent type of cancer that arises in the anal canal and the outer edges of the anus. This channel is a small tube located at the end of the rectum, through which stool leaves the body.
Anal cancer forms when a genetic mutation turns normal, healthy cells into abnormal ones. Healthy cells grow, multiply and die. In contrast, abnormal cells grow, multiply uncontrollably and form cancer.
The accumulation of these abnormal cells forms a mass called a tumor. Cancer cells invade neighboring tissues and can separate from their initial tumor and spread throughout the body in a process known as metastasis.
Anal canal cancer is closely related to a sexually transmitted infection called human papilloma virus or HPV: evidence of HPV is detected in most anal cancers. In this context, HPV is considered the most common cause of anal cancer.
Malignant tumors arise in different types of tissues, and squamous cell carcinoma is responsible for 85% of cases of anal canal tumors.
Anal cancer is rare and accounts for 1% to 2% of all colorectal tumors. Due to the low incidence, INCA (National Cancer Institute) does not provide statistics on new cases. According to the 2018 Cancer Mortality Atlas, there were 603 deaths (210 men and 393 women) as a result of this neoplasm.
Symptoms of anal canal cancer
Anal cancer can cause signs and symptoms such as rectal bleeding and anal pain.
Changes in bowel habits and the presence of blood in the stool are warning signs to seek medical advice.
The most commonly observed symptom is lively anal bleeding during defecation, associated with pain in the anus region. Other warning signs are itching, burning, unusual secretions, sores in the anal area, and fecal incontinence (inability to control the output of stool).
Diagnosis of anal canal cancer
The first step in diagnosing anal canal cancer is to perform a digital examination and, if necessary, an anoscopy and/or proctoscopy. In these exams, the doctor inserts a small speculum inside the anus to look for abnormalities or the proctoscope, which is a short, straight, rigid, hollow metal tube that usually has a small lamp mounted on the end.
If deemed necessary, the specialist may request a biopsy of a tissue sample to confirm the diagnosis.
Other exams, such as magnetic resonance imaging, may be requested as a way to assess the extent of the tumor and assist in choosing the best treatment.
In the past, surgery was the only treatment available to cure anal canal cancer, but it entailed a permanent colostomy in most cases.
Currently, most people are treated with a combination of chemotherapy and radiation, known as chemoradiotherapy. Although the combination of these approaches avoids colostomy in most cases and increases the chances of cure, it can also increase adverse effects. Therefore, it is important to discuss with the doctor about all possibilities and clear all doubts.
The combined approach usually eliminates the need for surgery, but depending on what stage the anal canal cancer is at, it may be indicated.
Some infections, such as those caused by HPV and the human immunodeficiency virus (HIV) are identified as responsible for the increased incidence of anal tumors. Other sexually transmitted diseases, such as condylomatosis, gonorrhea, genital herpes, and chlamydia, as well as anal sex, smoking, and chronic anal fistula (abnormal connection between the surface of the anal canal and the tissue around the anus, with purulent discharge) are related to the development of this type of cancer. Therefore, some ways of prevention include:
- Use a condom (condom) in all sexual relations;
- If possible, get the HPV vaccine;
- Cease smoking;
- Avoid the practice of anal sex;
- Pay attention to hygiene conditions and signs of chronic irritation of the anus.