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IAS 2011: People with HIV Have Double Risk for Non-Melanoma Skin Cancers

Several studies conducted in the era of effective antiretroviral therapy (ART) have shown that people with HIV have higher rates of non-AIDS-defining cancers, especially those caused by infectious pathogens such as human papillomavirus or hepatitis B or C.

It is unclear, however, whether non-melanoma skin cancers such as basal cell carcinoma and squamous cell carcinoma are also more common, since they are often not recorded in cancer registries.

As described in a poster presented at the 6th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention (IAS 2011) last month in Rome, Michael Silverberg from Kaiser Permanente Northern California and colleagues aimed to determine rates of non-melanoma skin cancers among HIV positive members of this large integrated healthcare system.

The researchers identified 6567 HIV positive participants and 36,887 HIV negative participants matched for age, sex, and race (all were Caucasian). Most (89%) were men, 72% were men who have sex with men, and the average age was about 42 years. The HIV positive group was more likely to smoke but less likely to be overweight.

Silverberg's team collected information from pathology reports on first biopsy-proven basal cell or squamous cell carcinomas. Participants were followed from first enrollment after 1996 (the year combination ART became widely available) until skin cancer diagnosis, loss to follow-up, or December 2008.

Results

• Rates of non-melanoma skin cancer were significantly higher for HIV positive compared with HIV negative study participants:
  • 1188 HIV positive and 661 HIV negative people were diagnosed with basal cell carcinoma, for a rate ratio of 2.0 or twice the risk.
  • 410 HIV positive and 186 HIV negative people were diagnosed with squamous cell carcinoma, for a rate ratio of 2.6.
• Skin cancer rates increased steadily as CD4 cell counts fell:
  • Basal cell carcinoma:
    • HIV negative: 661 cases per 100,000 person-years (PY);
    • HIV positive, CD4 count > 500 cells/mm³: 1035 per 100,000 PY;
    • HIV positive, 201-499 cells/mm³: 1263 per 100,000 PY;
    • HIV positive, < 200 cells/mm³: 1327 per 100,000 PY.
  • Squamous cell carcinoma:
    • HIV negative: 186 cases per 100,000 person-years;
    • HIV positive, > 500 cells/mm³: 266 per 100,000 PY;
    • HIV positive, 201-499 cells/mm³: 445 per 100,000 PY;
    • HIV positive, < 200 cells/mm³: 649 per 100,000 PY.
• Overall, among HIV positive patients there were about 3 basal cell carcinoma cases for every 1 squamous cell carcinoma case, but this ratio varied by recent CD4 cell level:
  • 2 to 1 for < 200 cells/mm³;
  • 3 to 1 for 201-499 cells/mm³;
  • 4 to 1 for > 500 cells/mm³.
• HIV viral load and ART use were not significantly associated with development of basal cell or squamous cell carcinoma.

The investigators suggested that "The two-fold higher non-melanoma skin cancer risk in HIV patients may partly result from more screening or increased sun exposure," although it is unclear why the latter would be true.

"Squamous cell carcinoma risk may also be affected by alterations in the immune system," they added. This is in accordance with findings from other studies showing that past or present immune suppression increases cancer risk, though skin cancers are not known to have an infectious cause.

Investigator affiliations: Kaiser Permanente Northern California, Division of Research, Oakland, CA; National Cancer Institute, Division of Cancer Epidemiology and Genetics, Rockville, MD.

8/2/11

Reference

M Silverberg, W Leyden, M Warton, et al. HIV infection and non-melanoma skin cancer risk. 6th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention (IAS 2011). Rome, July 17-20, 2011. Abstract TUPE235.