373 Toward data-driven guidelines for Merkel cell carcinoma surveillance: Stage-specific recurrence risk from 535 patients

Merkel cell carcinoma (MCC) has an approximately 40% risk of recurrence after initial treatment, with stage at presentation greatly affecting the risk of recurrence. However, stage-specific data regarding risk of recurrence has not been published. We performed a detailed analysis of MCC recurrences on a cohort of 535 MCC patients, 187 of whom had a recurrence. At time of analysis, median follow-up was 715 days (range 0 days – 4,415 days), and 35% of patients had developed at least one recurrence. Stage-specific (AJCC 8th edition) 5-year recurrence risk was: 22% for pathological stage I; 38% for stage IIA/IIB; 40% for stage IIIA; 57% for stage IIIB. Among patients who developed a recurrence, the fraction of those recurrences that were distantly metastatic increased based on stage at presentation: 37% of patients originally presenting with pathological stage I had recurrences that were distantly metastatic; 55% of stage IIA/IIB; 83% of stage IIIA; 80% of stage IIIB. In addition to stage, chronic immune suppression was also an independent predictor of recurrence: such patients were 72% more likely to have recurrent disease than immune competent patients (HR 2.53, p < 0.001). With more advanced disease at presentation, the role of imaging studies becomes increasingly important. This is because the proportion of distant recurrences (often detectable only via imaging studies) increases with increasing stage. We anticipate these findings will help develop accurate, stage-specific surveillance guidelines that will aid in early detection of recurrent disease in higher risk patients while eliminating unnecessary patient visits and imaging studies in low risk patients.