Squamous cell carcinomas are the most commonly encountered (about 90% of all cases) anal cancers. Adenocarcinoma and other types are less common. Besides squamous cell carcinomas, many benign tumorous growths in the mucosa are frequently reported that are not cancerous. These may include polyps, skin tags, and anal warts.
Anal warts are mostly associated with the human papillomavirus (HPV) infection. Certain precancerous lesions, for example, anal intraepithelial neoplasia (AIN) (low and high grade) or carcinoma in situ (CIN) may develop in the anal canal, which may progress to anal cancer.
Similar to the screening of cervical cancer through Pap test, the screening for anal cancer can be performed using anal Pap test that can diagnose pre-cancerous changes in the anal mucosa and thus the development of invasive anal cancer can be prevented.
Anal Cancer Risk factors
HPV Virus Infection
Human papillomavirus (HPV) infection is the single most important risk factor which is associated with almost 85 to 95% of the cases of anal cancer. Although the incidence of HPV infection is very common, only a few cases progress to pre-cancerous anal lesions or invasive anal cancer. HPV is a group of about 150 DNA viruses, with high-risk subtypes including HPV-16 and HPV-18, reported in about 75% and 10% of all the cases of anal cancer, respectively. HPV consists of two proteins known as E6 and E7 which inactivate some tumor suppressor genes and lead to anal cancer.
Although anal warts are caused by different subtypes of HPV, individuals with a history of anal warts remain at high risk of developing the infection with high-risk HPV subtype, and thus, anal cancer.
People infected with HIV are at 15 to 35 times higher risk of developing anal cancer compared to the normal population.
Weak Immune System
Individuals with a weak immune system that may be due to any cause, for example, infection with human immunodeficiency virus (HIV), use of medicines that suppress the immune system after an organ transplantation, an autoimmune disorder, chronic steroid therapy, etc, are more prone to HPV infection and thus development of anal cancer.
Men or women who have receptive anal intercourse remain at high risk of developing anal cancer due to a high frequency of HPV infection reported in these people.
Multiple Sexual Partners
Individuals who have multiple sexual partners or have partners with multiple partners are considered to be at higher risk of developing anal cancer due to higher chances of sexually transmitted HPV infection.
History of cervical, vaginal or vulvar cancer
Women with a history of genital cancer that are mostly caused by HPV infection are also considered to be at increased risk of developing anal cancer.
Chronic tobacco chewing or cigarette smoking exposes the body to various carcinogens that suppress the immune system to fight against HPV infection and increase the risk of anal cancer.
Consumption of diet low in fruits and vegetables, in utero exposure to diethylstilbestrol (DES), history of a sexually transmitted disease, and chlamydial infection are other reported risk factors for anal cancer.
Apart from the above-listed risk factors, certain factors which can reduce the risk of anal cancer have also been reported. Such protective factors mainly include the use of intrauterine devices for birth control and HPV vaccination. Also quitting smoking may be helpful.
Now let’s read about treatment of anal cancer.