Ambient UVR exposure tops immunosuppression factors causing Merkel cell carcinoma

Key takeaways:

• 65.1% and 63.8% of Merkel cell carcinoma cases were attributed to ambient ultraviolet radiation exposure and Merkel cell polyomavirus.
• 2.5% were traced to HIV, organ transplants and chronic lymphocytic leukemia.

Ambient ultraviolet radiation exposure and Merkel cell polyomavirus were both attributed to the development of Merkel cell carcinoma, whereas HIV, organ transplants and lymphocytic leukemia were not, according to a study.

“Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine tumor of the skin.” Jacob T. Tribble, BA, of the division of cancer epidemiology and genetics at the National Cancer Institute, and colleagues wrote. “While several risk factors for MCC have been identified, no study has estimated the burden of MCC attributable to these risk factors.”

In their epidemiological assessment, Tribble and colleagues estimated the proportions of 38,020 MCC cases (38% women; 93% non-Hispanic white) diagnosed in the U.S. between 2001 and 2019 that can be attributed specifically to major immunosuppressing conditions —including HIV, solid organ transplantation and chronic lymphocytic leukemia (CLL) —ambient ultraviolet (UV) radiation exposure and Merkel cell polyomavirus (MCPyV).

Results showed that people with HIV, organ transplants and CLL were 2.78, 13.1 and 5.75 times, respectively, more likely to get MCC compared with the general population. However, because these conditions are so rare, the proportions of MCC cases attributable to these conditions totaled 0.2% (95% CI, 0.1%-0.3%) for HIV, 1.5% (95% CI, 1.4%-1.7%) for organ transplantations and 0.8% (95% CI, 0.5%-1.3%) for CLL. Overall, only 2.5% of MCC cases can be traced to these conditions.

On the other hand, there was a strong link between ambient UV radiation exposure levels and MCC, particularly among non-Hispanic white individuals, with 65.1% (95% CI, 63.6%-66.7%) of cases being traced to this risk factor. The incidence rates of MCC on the head and neck among white individuals exposed to both low and high ambient UV radiation levels compared with the general population were 4.05 and 4.91, respectively.

Lastly, according to a meta-analysis of a 19-case series, MCPyV was also a high-risk factor of MCC, with 63.8% (95% CI, 54.5%-70.9%) of cases being linked to the virus.

“The results of this study suggest that most MCC cases in the U.S. are attributable to MCPyV and/or ambient UVR exposure, with a smaller fraction attributable to three major immunosuppressive conditions,” the authors wrote. “As people with HIV and solid organ transplant recipients age, there may be a higher burden attributable to immunosuppression in the future.”