Over 65% of Merkel cell carcinoma cases in the United States may be attributed to ultraviolet radiation exposure, whereas 63.8% of them may be linked to the Merkel cell polyomavirus, according to a recent study. 

In the study, published in JAMA Dermatology, investigators assessed the proportion of Merkel cell carcinoma (MCC) cases in the United States attributable to immunosuppressive conditions, ultraviolet radiation (UVR), and Merkel cell polyomavirus (MCPyV). The study utilized population-based cancer registries, including the HIV/AIDS Cancer Match Study and the Transplant Cancer Match Study as well as meta-analyses of MCPyV prevalence in MCC tumors.

The investigators analyzed 38,020 MCC cases diagnosed between 2001 and 2019. Immunosuppressive conditions significantly increased MCC risk, with standardized incidence ratios of 2.78 for HIV, 13.1 for solid organ transplant recipients, and 5.75 for chronic lymphocytic leukemia (CLL). Despite these elevated risks, the population attributable fractions were small as a result of the low prevalence of these conditions: 0.2% of cases were attributable to human immunodeficiency virus, 1.5% to solid organ transplant, and 0.8% to CLL.

UVR exposure, assessed using county-level ambient UVR data merged with cancer registries, was linked to elevated MCC incidence among non-Hispanic White patients. The incidence rate ratios for MCC of the head and neck were 4.05 and 4.91 in lower and higher ambient UVR exposure areas, respectively. Overall, UVR accounted for 65.1% of MCC cases, highlighting its substantial role in disease risk.

A meta-analysis of 19 studies, encompassing 1,024 MCC tumor samples, determined that 63.8% of MCC cases were attributable to MCPyV. The pooled MCPyV prevalence was consistent across detection methods (62.0% for immunohistochemistry and 66.7% for polymerase chain reaction) and immune statuses (66.6% in patients who were immunocompromised vs 62.4% in those who were immunocompetent).

The study concluded that MCPyV and UVR exposure were the predominant contributors to MCC cases, while immunosuppressive conditions accounted for 2.5%. The investigators recommended further studies to explore the interaction between UVR and MCPyV and to evaluate targeted prevention approaches.

Full disclosures can be found in the published study.