Anatomic Variability in Patterns of Care for Locoregional Merkel Cell Carcinoma (MCC) Management at a Large Referral Center

Abstract

<h3>Purpose/Objective(s)</h3> MCC is a rare cutaneous malignancy. This study evaluates patterns of care and outcomes for head and neck (HN) vs. non-HN (NHN) MCC at a large referral center. <h3>Materials/Methods</h3> We identified 144 locoregionally-confined MCC patients (pts) who received curative intent radiation therapy (RT) between 2003-2021. Clinicopathologic variables were described and time to relapse events were assessed by the Kaplan-Meier method. <h3>Results</h3> Of 144 pts, 80 (56%) had HN and 64 (44%) had NHN MCC. HN pts were older (median 70; IQR 66-76 vs. 65; IQR 57-73, p<0.001) and more likely male (63; 79% HN vs. 39; 61% NHN, p=0.03). Stage (I-II 42; 53% HN vs. 27; 42% NHN, p=0.24) and unknown primary presentation were similar (16; 20% HN vs. 7; 11% NHN, p=0.17). For pts with known primary tumor, wide local excision (WLE) after biopsy was less common in HN pts (46; 72% HN vs. 57; 100% NHN, p<0.001). Including 5 HN pts with excisional biopsies, R1 margin status was more common in the HN (15; 31% vs. 7; 13%, p=0.03), while all 13 definitive RT pts had HN disease. Most patients in this overall cohort received RT to the primary site (62; 96% HN vs. 55; 96% NHN) with a higher median dose for HN pts overall (60 Gy HN; IQR 56-60 Gy vs. 50 Gy NHN; IQR 56-60 Gy, p<0.001) as well as for pts having WLE (56 Gy HN; IQR 50-60 Gy vs. 50 Gy NHN; IQR 50-60). Similar rates of clinically LN+ disease were observed between cohorts (cLN+, 24; 30% HN vs. 18; 28% NHN, p=0.86), but HN pts had fewer LN dissections (LND, 14; 58% HN vs. 16; 89% NHN, p=0.024). Adjuvant nodal RT was delivered to most cLN+ pts (14; 100% HN vs. 14; 88% NHN, p=0.49) but this dose was higher for HN pts (med 59 Gy, IQR 52-60 Gy vs. med 50 Gy, IQR 50-54 Gy, p=0.013). For cLN- pts, fewer HN pts had sentinel lymph node biopsy (SLNB, 30; 54% HN vs. 42; 91% NHN, p<0.001). Of those SLN+ (11; 37% HN vs. 14, 33% NHN; p=0.81), only 1 HN pt and 2 NHN pts had completion LND. More HN pts received nodal RT for SLN+ disease (11; 100% HN vs. 9; 64% NHN, P=0.009) and elective nodal RT following N0 disease (4; 21% HN, med 46 Gy [IQR 46-53 Gy] vs 0% NHN, p=0.02). Nodal RT dose for cLN- pts trended higher in HN pts (med 52.5 Gy, IQR 46-60 Gy vs. 50 Gy, IQR 50-50.4 Gy, p=0.059). Median follow up was 40 months (IQR 22-58 mo) with similar outcomes for HN and NHN pts (3-yr LC 92% vs. 94%, p=0.85; 3-yr NC 83% vs. 79%, p=0.32; 3-yr DFS 64% vs. 60%, p=0.39). <h3>Conclusion</h3> Different treatment approaches exist for MCC pts at our institution based on tumor location. HN management historically relied more on comprehensive RT with higher doses whereas NHN management involves more comprehensive surgery and less RT. Anatomic limitations likely contributed to variation in practice. Despite differences in management tumor control outcomes are similar. Further study into the optimal approach to maximize disease control while limiting toxicity is warranted.