WEDNESDAY, Nov. 27, 2024 -- Most Merkel cell carcinoma (MCC) cases in the United States are attributable to ambient ultraviolent radiation (UVR) exposure or Merkel cell polyomavirus (MCPyV), while only a small fraction of cases are attributable to immunosuppressive conditions, according to a study published online Nov. 27 in .

Jacob T. Tribble, from the National Institutes of Health in Rockville, Maryland, and colleagues estimated the population attributable fraction of MCC cases in the United States that were attributable to major immunosuppressive conditions.

Overall, 38,020 MCCs were diagnosed in the United States. The researchers found that MCC incidence was increased among people with HIV, organ transplant recipients, and patients with chronic lymphocytic leukemia (CLL) compared with the general U.S. population (standardized incidence ratios, 2.78, 13.1, and 5.75, respectively). Due to the rarity of these conditions, only 0.2, 1.5, and 0.8 percent of MCC cases were attributable to HIV, solid organ transplant, and CLL, respectively. MCC incidence was elevated among non-Hispanic White individuals compared with individuals of racial and ethnic minority groups at lower and higher ambient UVR exposure levels (incidence rate ratios, 4.05 and 4.91, respectively, for MCC on the head and neck). Almost two-thirds (65.1 percent) of MCCs were attributable to UVR; 63.8 percent of MCCs were attributable to MCPyV based on a meta-analysis of 19 case series.

"Although MCC risk is substantially elevated among people with HIV, a solid organ transplant, or CLL, only 2.5 percent of MCC cases were attributable to these three immunosuppressive conditions due to their low prevalence in the general population," the authors write.