Stage Distribution, Treatment Patterns, and Stage-Specific Survival in Merkel Cell Carcinoma before and after the Immunotherapy Era: A Seer Analysis (2004–2022)

Document Type

Conference Proceeding

Publication Date

5-27-2026

Publication Title

J Clin Oncol

Keywords

adult, aged, cohort analysis, conference abstract, diagnosis, drug therapy, ethnicity, female, human, human tissue, major clinical study, male, merkel cell carcinoma, middle aged, overall survival, radiotherapy, retrospective study, surgery, undertreatment

Abstract

e21556Background: 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.

Volume

44

Issue

16_Suppl

First Page

e21556

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