Narrow excision margins are appropriate for Merkel cell carcinoma when combined with adjuvant radiation: Analysis of 188 cases of localized disease and proposed management algorithm

Background: Merkel cell carcinoma (MCC) management typically includes surgery with or without adjuvant radiation therapy (aRT). Major challenges include determining surgical margin size and whether aRT is indicated. Objective: To assess the association of aRT, surgical margin size, and MCC local recurrence. Methods: Analysis of 188 MCC cases presenting without clinical nodal involvement. Results: aRT-treated patients tended to have higher-risk tumors (larger diameter, positive microscopic margins, immunosuppression) yet had fewer local recurrences (LRs) than patients treated with surgery only (1% vs 15%; P = .001). For patients who underwent surgery alone, 7 of 35 (20%) treated with narrow margins (defined as ≤1.0 cm) developed LR, whereas 0 of 13 patients treated with surgical margins greater than 1.0 cm developed LR (P = .049). For aRT-treated patients, local control was excellent regardless of surgical margin size; only 1% experienced recurrence in each group (1 of 70 with narrow margins ≤1 cm and 1 of 70 with margins >1 cm; P = .56). Limitations: This was a retrospective study. Conclusions: Among patients treated with aRT, local control was superb even if significant risk factors were present and margins were narrow. We propose an algorithm for managing primary MCC that integrates risk factors and optimizes local control while minimizing morbidity.