Microsatellitosis in Patients with Melanoma

Background: Microsatellitosis (mS) in melanoma has been considered a marker of unfavorable tumor biology, leading to the current American Joint Committee on Cancer staging of IIIB/C/D disease, despite few investigative studies of this entity limited by the small sample sizes and incomplete nodal microstaging. We sought to better characterize outcomes and prognostic factors in a multi-institutional cohort of patients with mS and nodal microstaging. Methods: The Sentinel Lymph Node Working Group cohort included 414 mS patients who underwent sentinel lymph node (SLN) biopsy. Cox regression analysis was used to evaluate the prognostic significance of established clinicopathologic characteristics. Melanoma-specific survival (MSS) of patients with mS was compared with 3002 similarly staged patients from the Surveillance, Epidemiology, and End Results (SEER) Program registry. Results: The median age of the mS cohort was 64.9 years; 39.6% were female. Median thickness was 3 mm, 40.6% of cases were ulcerated, and the SLN positivity rate was 46.7%. Increasing thickness, male sex, and SLN positivity were significantly associated with poorer MSS. Stage IIIB/C/D 5-year MSS rates were 86.3% (95% confidence interval [CI] 79.4–93.3%), 54.1% (95% CI 45.4–59.7%), and 44.2% (95% CI 25.4–63.0%), respectively. MSS survival for the stage IIIB mS cohort was significantly better than a similarly staged SEER cohort (5-year MSS of 70.1%, 95% CI 66.0–74.2%), while no significant difference was observed for the stage IIIC or D cohorts. Conclusions: SLN metastases are common and are a significant prognostic factor in patients with mS. Survival in stage IIIB patients with mS was considerably more favorable than their stage would otherwise suggest, which has important implications for decisions regarding adjuvant therapy for patients with mS.