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 US cancer registry data. During 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. Over 70% of MCCs occurred in people aged 70 years or older versus 37% of melanomas. An excess of MCCs and melanomas arose 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 1.15-1.20 for MCC and 1.24-1.49 for melanoma, comparing quintiles 3-5 vs. 1). Cancer-specific mortality was higher among patients with MCC than 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 allow for prompt treatment, clinicians should be alert in diagnosing these cancers.