What does this research mean for the field?

Recent improvements in Merkel cell carcinoma survival are driven primarily by within-stage survival gains, particularly in regional and distant disease, rather than by earlier diagnosis or stage migration. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

What question did this study set out to answer?

This research investigates the survival rates and treatment patterns of Merkel cell carcinoma before and after the introduction of immunotherapy.

May 30, 2026

Stage distribution, treatment patterns, and stage-specific survival in Merkel cell carcinoma before and after the immunotherapy era: A SEER analysis (2004–2022).

Key Points

This research investigates the survival rates and treatment patterns of Merkel cell carcinoma before and after the introduction of immunotherapy.
Retrospective cohort analysis of 5,969 Merkel cell carcinoma patients in the SEER database (2004–2022).
Defined eras as pre-immunotherapy (2004–2015) and during immunotherapy (2016–2022).
Analyzed overall survival with Kaplan–Meier and stage-specific Cox models, adjusting for age, sex, and race.
Overall survival improved significantly in the immunotherapy era, particularly in regional and distant disease stages.
Distant stage median overall survival increased from 10 to 12 months; regional stage median increased from 30 to 64 months, both with statistically significant hazard ratios (HR < 0.75).
Minimal changes in stage distribution were observed, indicating that improvements in survival are primarily due to better within-stage outcomes rather than migration to less advanced stages.

Abstract

e21556 Background: Merkel cell carcinoma (MCC) survival has improved in recent years. Whether this reflects earlier diagnosis or better stage-specific treatment is unclear. Methods: We performed a retrospective cohort study of MCC in the SEER database (2004–2022). Eras were defined as pre-immunotherapy proxy (Pre-IO, 2004–2015) and IO-era proxy (2016–2022). Stage at diagnosis was categorized as localized, regional, distant, or unknown (Summary Stage). Overall survival (OS) was assessed using the Kaplan–Meier method and stage-specific Cox models, adjusted for age (<65, 65–79, ≥80), sex, and race/ethnicity. Local therapy patterns (surgery, radiation) for localized/regional cases were examined by era and age. Results: Among 5,969 MCC patients (3,313 Pre-IO; 2,656 IO-era), stage distribution was localized 54.7%, regional 26.9%, distant 9.8%, unknown 8.6%. Compared with Pre-IO, the IO-era showed more regional (24.3%→30.2%; +5.8 pp) and less localized disease (56.6%→52.3%; −4.3 pp); distant stage was stable. Stage-specific survival improved in the IO-era proxy. Distant: median OS 10→12 mo; 2-yr OS 24.2%→40.6%; 5-yr OS 14.0%→23.4%; adjusted HR 0.75 (p=0.004). Regional: median OS 30→64 mo; 2-yr OS 54.5%→69.6%; 5-yr OS 38.0%→51.0%; HR 0.71 (p<0.001). Localized: median OS 71 mo→NR; 2-yr OS 72.5%→76.6%; 5-yr OS 53.3%→58.1%; HR 0.91 (p=0.11). Decomposition of the overall 2-yr OS (61.8%→69.1%) showed a minimal stage-shift effect (−0.61 pp) and gains driven by within-stage survival (+7.97 pp). Treatment patterns indicated age-related de-intensification. In localized IO-era MCC, surgery + RT occurred in 49.4% (<65) vs 27.4% (≥80). In regional MCC ≥80, surgery+RT declined (53.0%→42.1%) while neither therapy increased (7.1%→14.5%). Conclusions: MCC stage distribution showed minimal stage migration, yet OS improved substantially after 2016—especially in Regional and Distant disease. Survival gains were driven primarily by within-stage improvements rather than stage migration. Persistent age-related differences in local therapy suggest undertreatment of older adults. OS Pre-IO proxy vs IO-era proxy by stage. Stage Median OS (mo) 2-yr OS % 5-yr OS % Adjusted HR P value Localized 71→NR 72.5→76.6 53.3→58.1 0.91 0.11 Regional 30→64 54.5→69.6 38.0→51.0 0.71 <0.001 Distant 10→12 24.2→40.6 14.0→23.4 0.75 0.004 Unknown 31→34 55.8→52.0 35.6→38.8 1.06 0.66

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