HIV doesn't increase risk of melanoma, but immune suppression associated with risk of rarer skin cancers

HIV-related immune suppression does not increase the risk of melanoma, one of the most common types of skin cancer, American investigators report in the January 23^rd edition of AIDS. However, they did find that AIDS patients had a higher risk of developing two rare skin cancers, Merkel cell carcinoma and appendageal carcinomas. The investigators believe that their results “suggest a need for guidelines aimed at the prevention and early detection of skin cancers in HIV-infected individuals”.

HIV-positive individuals with suppressed immune systems have an increased risk of developing cancer. The most important cancers seen in people with HIV are related to infections, for example Kaposi’s sarcoma (due to HHV-8), non-Hodgkin’s lymphoma (due to Epstein-Barr virus) and anogenital cancers (caused by certain strains of human papilloma virus).

Infection-related cancers also occur more often in organ recipients who have been treated with immunosuppressive drugs. Increased rates of skin cancer, most notably melanoma, have also been observed in this group of individuals. Aggressive melanomas have also been reported in people with HIV. Increased exposure to UV radiation from the sun and immune suppression have been suggested as possible causes. Furthermore, there is also some evidence that people with HIV have an increased prevalence of rarer skin cancers, such as Merkel cell carcinoma and appendageal carcinomas.

To gain a better understanding of the risk of skin cancer amongst HIV-positive patients who had been diagnosed with AIDS, US researchers designed a study that compared the risk for AIDS patients of three cancers (melanoma, Merkel cell carcinoma and appendageal carcinomas) with the risk for the general population.

Their study population was derived from the HIV/AIDS Cancer Match study that links HIV and general cancer registry databases in nine US states. Just under 400,00 HIV-positive patients diagnosed with AIDS between 1980 and 2004 were included in the analysis. The investigators checked these databases for cases of cancer of the skin in the five years before and the five years after AIDS was diagnosed.

Results showed that patients with AIDS had a 30% increase in the risk of developing melanoma. This increased risk did not reach statistical significance. Nor did the risk of melanoma increase over time as a patient’s immune system weakened and CD4 cell count declined, suggesting to the investigators that the modest elevation in risk of this cancer they observed was not related to immune deficiency.

White gay men and other men who have sex with men were the group most likely to develop melanoma (odds ratio, 1.7, 95% CI 1.2 to 2.4 vs other groups). Exposure to UV radiation was identified as an independent risk factor for melanoma (p = 0.0005).

The investigators suggest that the modest increase in the risk of melanoma seen in gay and other men who have sex with men with AIDS was most likely due to “recreational sun exposure or the use [of] tanning beds.” They also suggest that the increased surveillance of this population for Kaposi’s sarcoma could have increased the detection rate of early melanoma lesions.

However, patients with AIDS were significantly more likely to be diagnosed with both Merkel cell carcinoma (standardised incidence ratio [SIR] = 11, 95% CI 6.3 to 17) and appendageal carcinomas (SIR = 4.2, 95% CI 2.5 to 6.7). Both these cancers were, however, rare (17 cases each of Merkel cell carcinoma and appendageal carcinomas compared to 292 cases of melanoma).

Gay and other men who have sex with men had a higher risk of appendageal carcinomas than other groups (SIR = 6.8, 95% CI 3.6 to 12). As with melanoma, the risk of this cancer was associated with increased levels of exposure to UV light.

Risk of appendageal carcinoma also increased with increasing time (p = 0.03), suggesting an association with immune suppression.

The greatly increased risk of Merkel cell carcinoma in people with AIDS suggested to the investigators that “immunological mechanisms” were an important risk factor. They note “Merkel cell carcinoma risk is also elevated among immunosuppressed transplant recipients.”

The investigators conclude, “the greatly increased risk of Merkel cell carcinoma and appendageal carcinomas…among people with AIDS points to immunosuppression as a major risk factor for these cancers.”