Adjuvant Regional Nodal Radiation in Sentinel Lymph Node Positive Merkel Cell Carcinoma without Completion Lymph Node Dissection

Abstract

Merkel cell carcinoma (MCC) is associated with high risk for nodal involvement. Sentinel lymph node biopsy (SLNB) is standardly used to evaluate the draining nodal basin. Adjuvant radiation (RT) to the primary site and involved nodal region is used to increase locoregional control. Omission of completion lymph node dissection (CLND) in sentinel node positive patients when RT is planned is controversial. Our institutional practice has shifted to SLNB followed by RT without CLND in SLNB+ pts without bulky disease. This retrospective study aimed to evaluate outcomes in clinically node negative, SLNB+ pts who were treated with adjuvant RT alone without CLND. Hypothesis: We hypothesized adjuvant regional nodal RT without CLND would provide adequate locoregional tumor control in pts with clinically node negative, but SLNB+ MCC. Clinically node negative (either by exam or imaging) MCC pts who underwent wide local excision and had SLNB+ and no CLND at our institution from 2006 to 2017 were included for analysis. SLNB was completed with lymphoscintigraphy with technetium in all pts. Patient, clinical, and pathologic variables were evaluated. Local and regional control, rate of distant metastases, and overall survival (OS) were calculated with survival estimates determined by Kaplan-Meier statistics. A total of 16 pts were eligible for analysis with a median follow-up of 1.6 years (Range: 3 months to 6.9 years). The majority of patients were male (n=10), and median age at time of diagnosis was 72.5y (66.3 to 82y). Primary tumor location was lower extremity (n=7), upper extremity (6), head and neck (2), and truncal (1). Based on AJCC 7th edition, primary tumor stage was T1 (n=4), T2 (n=11) and T3 (n=1). Median number of SLNB+ nodes was 2 (range 1-3). The extent of metastatic foci ranged from isolated tumor cells to 2cm. There were 4 pts with nodal extracapsular extension. All pts had negative surgical margins. 15/16 pts completed adjuvant radiation to the primary post-operative bed and regional nodal basin. 1 pt declined adjuvant RT and pursued supportive care. 2 pts also received adjuvant carboplatin and etoposide. Median dose to the primary post-operative bed and regional nodal basin was 56Gy (range 52-60Gy) and 53Gy (range 50-56Gy), respectively. There were no recurrences at the primary or regional sites. Three patients developed distant disease with a median time to distant disease of 7.6 months. Median OS was 6.9 years. These findings are consistent with previous studies that show low rates of locoregional failure with SLNB+ disease managed by adjuvant RT without CLND. Implications for practice: This retrospective study further supports the use of regional adjuvant RT for locoregional control without the routine need for completion therapeutic lymph node dissection in clinically node negative MCC pts.