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Background: Merkel cell carcinoma (MCC) is a rare cutaneous malignancy for which factors predictive of disease-specific survival (DSS) are poorly defined. Methods: Patients from six centers (2005–2020) with clinical stage I–II MCC who underwent sentinel lymph node (SLN) biopsy were included. Factors associated with DSS were identified using competing-risks regression analysis. Risk-score modeling was established using competing-risks regression on a training dataset and internally validated by point assignment to variables. Results: Of 604 patients, 474 (78.5%) and 128 (21.2%) patients had clinical stage I and II disease, respectively, and 189 (31.3%) had SLN metastases. The 5-year DSS rate was 81.8% with a median follow-up of 31 months. Prognostic factors associated with worse DSS included increasing age (hazard ratio [HR] 1.03, p = 0.046), male sex (HR 3.21, p = 0.021), immune compromise (HR 2.46, p = 0.013), presence of microsatellites (HR 2.65, p = 0.041), and regional nodal involvement (1 node: HR 2.48, p = 0.039; ≥2 nodes: HR 2.95, p = 0.026). An internally validated, risk-score model incorporating all of these factors was developed with good performance (AUC 0.738). Patients with ≤ 4.00 and > 4.00 points had 5-year DSS rates of 89.4% and 67.2%, respectively. Five-year DSS for pathologic stage I/II patients with > 4.00 points (n = 49) was 79.8% and for pathologic stage III patients with ≤ 4.00 points (n = 62) was 90.3%. Conclusions: A risk-score model, including patient and tumor factors, based on DSS improves prognostic assessment of patients with clinically localized MCC. This may inform surveillance strategies and patient selection for adjuvant therapy trials. [ABSTRACT FROM AUTHOR]

Background: Sentinel lymph node biopsy (SLNB) is routinely recommended for clinically localized Merkel cell carcinoma (MCC); however, predictors of false negative (FN) SLNB are undefined. Methods: Patients from six centers undergoing wide excision and SLNB for stage I/II MCC (2005–2020) were identified and were classified as having either a true positive (TP), true negative (TN) or FN SLNB. Predictors of FN SLNB were identified and survival outcomes were estimated. Results: Of 525 patients, 28 (5.4%), 329 (62.7%), and 168 (32%) were classified as FN, TN, and TP, respectively, giving an FN rate of 14.3% and negative predictive value of 92.2% for SLNB. Median follow-up for SLNB-negative patients was 27 months, and median time to nodal recurrence for FN patients was 7 months. Male sex (hazard ratio [HR] 3.15, p = 0.034) and lymphovascular invasion (LVI) (HR 2.22, p = 0.048) significantly correlated with FN, and increasing age trended toward significance (HR 1.04, p = 0.067). The 3-year regional nodal recurrence-free survival for males >75 years with LVI was 78.5% versus 97.4% for females ≤75 years without LVI (p = 0.009). Five-year disease-specific survival (90.9% TN vs. 51.3% FN, p < 0.001) and overall survival (69.9% TN vs. 48.1% FN, p = 0.035) were significantly worse for FN patients. Conclusion: Failure to detect regional nodal microscopic disease by SLNB is associated with worse survival in clinically localized MCC. Males, patients >75 years, and those with LVI may be at increased risk for FN SLNB. Consideration of increased nodal surveillance following negative SLNB in these high-risk patients may aid in early identification of regional nodal recurrences. [ABSTRACT FROM AUTHOR]