Disparities in survival and tumor characteristics in patients with single and multiple primary Merkel cell carcinomas

Patients with Merkel cell carcinoma (MCC) are at risk of developing a subsequent primary MCC, but its profile and survival impact remain unclear.

To describe the epidemiologic profile and evaluate the prognosis of patients with multiple primary Merkel cell carcinoma (MPMCC).

This retrospective cohort study used data from the Surveillance, Epidemiology, and End Results Program (2004-2021). Standardized incidence ratios were calculated to estimate the risk of subsequent MCC. Multivariable Cox models with a time-varying covariate were applied to compare survival between patients with single and multiple primary MCC.

Of 9536 patients with MCC, 130 (1.4%) developed MPMCC. MCC survivors had a nearly 60-fold increased risk of subsequent MCC (standardized incidence ratio = 61.8; 95% confidence interval [CI], 50.2-75.3), with 78.5% diagnosed with a second primary MCC within 5 years. In patients with MPMCC, the median tumor size decreased from 20.0 mm at first diagnosis to 15.0 mm at the second (P = .038). MPMCC was associated with worse overall (hazard ratio = 1.64; 95% CI, 1.31-2.05) and cancer-specific survival (hazard ratio = 2.64; 95% CI, 1.91-3.65).

Retrospective design and potential misclassification of MPMCC.

MPMCC is associated with significantly worse overall and cancer-specific survival, supporting the need for intensified follow-up strategies.