Late subsequent Merkel cell carcinoma after 21 years of the first primary diagnosis: When to de-escalate surveillance?

Key Clinical Message: Merkel cell carcinoma (MCC) presents challenges in surveillance due to varied recurrence rates and uncertain follow-up protocols, especially in late recurrent cases. These cases need personalized monitoring strategies beyond traditional timelines, such as clinical and molecular factors, in order to optimize patient outcomes. Abstract: Merkel cell carcinoma (MCC) is a rare, aggressive skin cancer with neuroendocrine differentiation with a propensity for recurrence following initial treatment. Surveillance strategies for MCC patients lack specificity, and the duration of surveillance remains uncertain, posing challenges in identifying appropriate follow-up intervals. Therefore, we present a 94-year-old woman, with history of stage IA MCC in her left nasal wall 21 years prior, that presented with a dome-shaped eroded nodule on her left fifth finger. Biopsy showed characteristic MCC features with positive immunohistochemistry for CD56, synaptophysin, and CK20 (perinuclear dotting). The patient opted against further imaging or lymph node biopsy and underwent Mohs micrographic surgery. To date, there has not been any evidence of recurrence at previous sites or development of new primary lesions. This case underscores the need for ongoing surveillance despite long disease-free intervals. It also stands out as the case demonstrating the longest latency/recurrence-free interval following the initial diagnosis of MCC in the literature. While most recurrences occur within the first few years post-diagnosis, our case highlights the exceptional nature of late recurrences and prompts reevaluation of surveillance protocols. Current guidelines recommend surveillance for up to 3 years post-treatment, but factors, such as patient demographics and tumor characteristics, may warrant extended monitoring periods. Emerging biomarkers, such as Merkel cell polyomavirus status and circulating tumor DNA, show promise in predicting and monitoring recurrences, but their utility in late recurrence detection requires further investigation.