Is CTLA4 targeting the Achilles’ heel of Merkel cell carcinoma?

e21567 Background: Merkel Cell Carcinoma (MCC) is a cutaneous malignancy with neuroendocrine differentiation, linked to infection with polyomavirus (MCPyV) in 80% of cases. PD1 inhibitors have recently been approved for this indication with ORR, 33-56%; CR, 11-24%; PFS, about 17 months; OS, about 12 months. Nivolumab was tested in the neoadjuvant setting with similar responses with pathological CR, 47%. Methods: Adjuvant pilot study (NCT03798639) with two immunotherapy regimens administered for one year to patients with completely resected MCC at high risk of recurrence (primary lesion of 2 cm or greater, positive or close margins ( < 2 cm), perineural or lymphovascular invasion, mitotic index ≥ 20 mitotic figures per mm2, lymph node involvement (stage pIIIA or pIIIB) with or without extracapsular extension, or completely resected stage IV disease). Arm 1, nivolumab 480 mg q 4 wks and radiation therapy (RT) 50-60 Gy in 25-30 fractions, per standard of care. Arm 2, nivolumab 240 mg q 2 wks and ipilimumab 1 mg/kg q 6 wks. Primary objective was feasibility and completion of treatment in this population. Safety profile (CTCAE v5.0) and recurrence-free survival (RFS) after 18 months were secondary endpoints. Patients were randomly allocated 1:1. Results: Ten patients were screened from January 2019 until April 2020, when COVID put the study on hold and the sponsor discontinued the free drug supply. Seven were enrolled. Four were allocated to Arm 1 and three to Arm 2. Patient characteristics in Table. All patients have completed treatment and are in follow-up. Arm 1: all four patients completed radiation therapy and immunotherapy with no dose modifications or delays. Arm 2: one patient had nivolumab delayed 2 weeks for cellulitis, and another missed the last four last doses of nivolumab for cholecystitis and pancreatitis requiring surgery, unrelated to the immunotherapy. Adverse events (AE) were as expected. Arm1 caused more grade 2 and 3 AEs then Arm2 (no grade 3). One patient each discontinued treatment, in Arm 1 for progression and Arm 2 for immunotoxicity (temporal arteritis grade 2). One recurrence was observed in Arm 1 and none in Arm 2. Conclusions: The number of patients expected to recur at 1 year is 20%. Our observed data is insufficient to establish efficacy. However with no patient recurring in the ipilimumab arm after 18 months of follow-up and lower observed side effects, we would favor this regimen for the next trial. Clinical trial information: NCT03798639. [Table: see text]