Postoperative, Single-Fraction Radiation Therapy in Merkel Cell Carcinoma of the Head and Neck

Abstract

Purpose: Conventionally fractionated, postoperative radiation therapy (cPORT; 50 Gy in 25 fractions) is considered for patients with Merkel cell carcinoma (MCC) to improve locoregional control. However, cPORT is associated with acute toxicity, especially in the head and neck (H&N) region, and requires daily treatments over several weeks. We previously reported high rates of durable local control with minimal toxicity using 8-Gy single-fraction radiation therapy (SFRT) in the metastatic setting. We report early results on a cohort of patients with localized H&N MCC who received postoperative SFRT if a cPORT regimen was not feasible.

Methods and materials: Twelve patients with localized MCC of the H&N (clinical/pathologic stages I-II) and no prior radiation therapy to the region were identified from an institutional review board-approved prospective registry who underwent surgical resection followed by postoperative SFRT. Time to event was calculated starting from the date of resection before SFRT. The cumulative incidence of in-field locoregional recurrences and out-of-field recurrences was estimated with death as a competing risk.

Results: Twelve patients with H&N MCC were identified with clinical/pathologic stages I-II H&N MCC. Median age at diagnosis was 81 years (range, 58-96 years); 25% had immunosuppression. At a median follow-up of 19 months (range, 8-34), there were no in-field locoregional recurrences. A single out-of-field regional recurrence was observed, which was successfully salvaged. There were no MCC-specific deaths. No radiation-associated toxicities greater than grade 1 (Common Terminology Criteria for Adverse Events v5) were observed.

Conclusions: Preliminary data suggest that SFRT could offer a potential alternative to cPORT to treat the primary site for localized H&N MCC, particularly in elderly or frail patients, with promising in-field local control and minimal toxicity. Further data with validation in larger cohorts are needed to confirm the sustained safety and efficacy of postoperative SFRT.

Figure 1

(A-B) Patient no. 5 is an 81-year-old immunosuppressed man with a history of clinical stage I Merkel cell carcinoma of the right cheek status post-wide local excision with negative margins and a technically failed sentinel lymph node biopsy who elected to undergo adjuvant 8-Gy SFRT to his primary surgical tumor bed site with electrons. Four months after SFRT, he exhibited out-of-field regional failure in the lymph nodes in (C) the parotid, (D) level 2A, and (E) level 5. He was successfully salvaged with surgical resection followed by adjuvant conventional fractionated proton radiation therapy. He never failed within his initial SFRT field. Abbreviation: SFRT = single-fraction radiation therapy.

Figure 2

Freedom from in-field (100%) and out-of-field (92%) locoregional recurrence in patients treated with single-fraction radiation therapy.