Most anal cancers trace back to a virus that a vaccine targets
Anal cancer is uncommon, about half a percent of new US cancers, but one estimate attributes roughly 90 percent of cases to human papillomavirus, the same virus behind most cervical cancer. That link reshaped both prevention and treatment, and in 2010 an HPV vaccine was approved in the United States specifically against it.
Around 10,930 Americans are diagnosed each year, usually after age 45, and women more often than men. Cases have been rising since the 1990s. Symptoms include bleeding, a lump near the anus, pain, itching, discharge or a change in bowel habits. Most tumours are squamous cell carcinomas arising near the junction where two types of lining meet; rarer forms include adenocarcinoma and melanoma.
The viral connection came from tissue studies. Tumour samples from Denmark and Sweden often carried the high-risk HPV types linked to cervical cancer, and another study found HPV-16 and similar strains in 84 percent of specimens. Behaviour that raises HPV exposure raises risk, as does immune suppression, often from HIV. Smoking is an independent factor: in research led by epidemiologist Janet Daling, current smokers had about four times the risk, and more than half of patients smoked, against roughly 23 percent of comparison subjects. The mechanism is unknown, though smoking may blunt the programmed death of abnormal cells or weaken immunity.
Prevention now leans on vaccination and screening. American regulators cleared Gardasil in 2010 for protecting people aged 9 to 26 against this cancer and the lesions that precede it. Anal Pap tests modelled on cervical screening have been studied in high-risk groups; among women with a history of cervical cancer or severe cervical precancer, more than 30 percent had abnormal results.
Treatment has become far less drastic. Surgery once often meant removing the sphincter muscles and living with a permanent colostomy. The current standard combines chemotherapy with radiation, which usually preserves the sphincter and yields excellent cure rates, though some people still face incontinence. In the United States the five-year survival rate is 71 percent.
Source: Anal cancer
