Merkel cell carcinoma (MCC) primary site has been incompletely investigated as a potential prognostic factor.

To determine the incidence of MCC disease-specific death by tumor primary site.

Retrospective analysis of the Survival, Epidemiology, and End Results (SEER) database (1973-2016). MCC patients were grouped by tumor primary site and a competing risks analysis was performed to test the impact of primary site on disease-specific death. Cumulative MCC-specific mortality incidence (CMMI) at five years was estimated for each primary site.

Of the 9407 MCC patients identified, 6305 (67.0%) patients had localized disease, 2397 (25.5%) had regional metastasis, and 705 (7.5%) had distant metastasis. Tumor primary site was predictive of CMMI and varied by stage at diagnosis. Tumors involving the scalp/neck carried the highest CMMI among localized MCC (26.0%). Tumors involving the lip had the highest CMMI among MCC with regional metastasis (56.7%) and distant metastasis (82.1%).

Tumor size data were missing for a large proportion of patients, precluding stratification by stage according to current American Joint Committee on Cancer guidelines.

Probability of MCC disease-specific death varies by primary site, and tumor primary site may be useful as a prognostic indicator for MCC.