A Comparative Study of Merkel Cell Carcinoma and Melanoma Incidence and Survival in the United States, 2000-2021.

Merkel cell carcinoma (MCC) and melanoma are important contributors to skin cancer mortality in the United States. We evaluated their epidemiology using the United States cancer registry data. In 2000-2021, 19,444 MCCs and 646,619 melanomas of the skin were diagnosed. Ninety percent of MCCs and 95% of melanomas were in non-Hispanic White individuals. More than 70% of MCCs versus 37% of melanomas occurred in people aged ≥70 years. Excess MCCs and melanomas were observed on the head and neck (observed:expected: MCC, 5.15; melanoma, 2.47). Among non-Hispanic White individuals, ambient UVR exposure was associated with melanoma arising on the head and neck (incidence rate ratios of 1.15-1.20 for MCC and 1.24-1.49 for melanoma, comparing quintiles 3-5 with quintile 1). Cancer-specific mortality was higher among patients with MCC than among those with melanoma (hazard ratio = 2.33, 95% confidence interval = 2.26-2.42) but improved in both groups after 2011 when BRAF and checkpoint inhibitors were introduced. In conclusion, melanoma exhibited stronger associations with race and ambient UVR exposure, while MCC was more likely to arise on the head and neck (perhaps reflecting the distribution of precursor cells). To ensure prompt treatment, clinicians should be on alert when diagnosing these cancers.