Should Sentinel Lymph Node Biopsy Status Guide Adjuvant Radiation Therapy in Patients With Merkel Cell Carcinoma?

Radiation of the draining lymph node basin remains controversial for Merkel cell carcinoma, particularly in the era of sentinel lymph node biopsy (SLNB).

Based on a 20-year experience using SLNB-guided adjuvant radiation therapy (RT), we conducted a retrospective review of clinically node-negative patients testing 2 hypotheses: (1) whether nodal RT could be safely omitted in SLNB-negative Merkel cell carcinoma and (2) whether the excised primary site should always be radiated. Clinically node-positive patients were excluded.

Among 57 clinically node-negative patients who underwent SLNB and wide local excision (WLE), 42 (74%) had a negative SLNB, and 15 (26%) had a positive SLNB. At a median follow-up of 43 months (range, 5-182), SLNB-negative patients irradiated to the primary site had improved 4-year disease-specific survival (100% vs 65%, P = .008), local recurrence-free survival (100% vs 76%, P = .009), and distant recurrence-free survival (100% vs 75%, P = .008), but not overall survival (87.5% vs 57.7%, P = .164) compared with SLNB-positive patients receiving comprehensive RT. Among SLNB-negative patients treated with WLE only, 67% (6/9) had a disease relapse, half of which were local relapses (33%).

In this single-institution retrospective review, after negative SLNB and WLE, RT given only to the primary site provided 100% disease control without a need for nodal RT. Among SLNB-negative patients who had WLE, omission of postoperative primary-site RT was associated with 67% cancer relapse, of which half was local.