March 21, 2013 | by Hiu Chung So
Anal cancer represents only a small portion of digestive tract cancers — 7,080 out of 290,200 cases, according to American Cancer Society estimates — but its incidence rate has more than doubled since the mid- to late 1990s.
This has caught the attention of several City of Hope researchers, who are curious about the alarming trend and its potential causes. So they delved into the figures compiled by the National Cancer Institute’s Surveillance, Epidemiology and End Results database to seek answers.
The study and its results were published online in the Journal of Clinical Oncology on March 18. In the article, the researchers found that for squamous cell carcinoma in the anal canal (SCCA) — the most common type of anal cancer — the average incidence rate until 1997 was 1.2 cases per 100,000 Americans, with an annual increase of 2.4 percent. After 1997, that went up to 2.8 cases per 100,000 Americans with an annual increase of 7.2 percent.
“The dramatic rise may be partly due to early detection through patient screening,” said lead researcher Rebecca Nelson, Ph.D., assistant research scientist in the Division of Biostatistics. “But this time point also coincides with HIV’s impact on the acquisition and persistence of HPV, the primary cause of SCCAs.”
In the study, Nelson and her colleagues cited research showing that 65 to 89 percent of SCCAs are linked to human papillomavirus (HPV) infection.
And just as there's a latent period between a HIV infection and symptomatic AIDS, Nelson said, there is also a similar lag time between contracting HPV, which often co-exists with HIV, and the cellular changes that lead to anal cancer.
Also, because being immunosuppressed is another risk factor for developing SCCAs, a person infected with both HIV and HPV is even more likely to get anal cancer.
Both factors help explain how the HIV epidemic of the early 1980s may be responsible for the SCCA incidence and growth spike from 1997 onward. However. Nelson said further research is needed to confirm this connection, including HIV/HPV infection information for those diagnosed with SCCA, studies into patients' lifestyle choices and anal cancer screening participation rates.
In the meantime, Nelson suggests that individuals with higher risk consider being screened for anal cancers. In addition to HPV infection and being immunocompromised, other risk factors include having multiple sex partners, especially before the age of 30, engaging in receptive anal sex and sex without condoms.
Nelson also recommends that the public get vaccinated against HPV in accordance to Centers for Disease Control and Prevention recommendations, which will prevent the spread of HPV and, hopefully, lower the incidences of anal and other related cancers.