Anal cancer is a highly preventable type of cancer given its connection to human papillomavirus (HPV), a group of 150 related viruses that infect the surface of the skin, which can include the genitals, anus, mouth and throat.
The majority of squamous cell anal cancers (the most common form of anal cancer which affects the cells that line the anus) are caused by an HPV infection. HPV infections are often transmitted through skin-to-skin contact, including sexual activity and are incredibly common. In fact, 8 out of 10 people will be infected with the virus at one point in their lives. Fortunately, in most cases, the body can clear the infection on its own.
However, some infections may become chronic, and if they are linked to what are known as “high-risk” HPV types, they can lead to certain cancers like anal cancer or of the cervix, vulva, penis, mouth, or throat. Low-risk types may cause growths or warts but aren’t linked to cancer, but subtype HPV-16, for example, is most likely to cause anal cancer. Oftentimes, patients with anal cancer do not know that they have HPV until they are diagnosed with cancer and are tested.
HPV and cancer prevention
Fortunately, HPV vaccines are highly effective at preventing the types of HPV that cause cancer. The vaccine is recommended for children starting at age nine and young adults up to age 26.
“Hopefully there will be a generation of children who don’t get HPV-related cancers,” says Dana-Farber gastrointestinal oncologist Benjamin L. Schlechter, MD.
The U.S. Centers for Disease and Prevention (CDC) does not recommend vaccination for adults over 26 because they have often already been exposed to HPV, and therefore the vaccine will provide less benefit. Nonetheless, adults may still choose to get vaccinated after a conversation with their physician about the benefits and risks.
“It’s incredibly safe and incredibly effective,” says Schlechter. “HPV-related cancer are relatively rare cancers, but just because it’s rare doesn’t mean we shouldn’t focus on prevention.”
How is HPV-positive anal cancer treated?
HPV-positive anal cancer is treated in the same way as other anal cancers, but generally has better outcomes. It is not clear if this is because HPV-positive cancers respond to treatment better. This association may be because HPV-negative cancers more often affect older patients and younger patients generally have better treatment outcomes.
Chemotherapy and radiation for early-stage anal cancers is highly effective and cures about 88 percent of cases. Most patients receive chemotherapy with 5-fluorouracil with mitomycin C, but some patients may receive capecitabine instead of 5-fluorouracil or cisplatin instead of mitomycin C. For advanced disease, radiation may or may not be included in the treatment plan. Even with this success rate, researchers at Dana-Farber and other cancer centers are always seeking to improve treatments.
Treatments are improving for advanced disease. For example, a 2020 study recently found that the relatively newer chemotherapy regimen called carboplatin with paclitaxel has less side-effects and longer survival than the older cisplatin regimens. Investigators at Dana-Farber are also looking at how immunotherapies like pembrolizumab and nivolumab can be used to treat anal cancer. There is already evidence that it may help patients with late-stage anal cancer and researchers are thinking of ways in which these new treatments can be used earlier in treatment protocols along with chemotherapy and radiotherapy.
About the Medical Reviewer
Dr. Schlechter is a medical oncologist who specializes in gastrointestinal cancers including colorectal cancer, anal cancer, pancreatic cancer, and neuroendocrine cancers, among others. He is a former intern, resident, chief resident and fellow at Beth Israel Deaconess Medical Center as well as a member of the faculty at Harvard Medical School. In the past he was the Director of Inpatient Hematology and Oncology at Beth Israel Deaconess Medical Center as well as the Assistant Program Director of the Internal Medicine Residency Program. His work at Dana-Farber focuses on providing excellent patient care while trying to advance the treatment of gastrointestinal cancer patients.