Severe necrotizing myositis associated with long term anti-neoplastic efficacy following nivolumab plus ipilimumab combination therapy.

Immune-related adverse events (irAEs), have been reported under immune checkpoint inhibitors. Nivolumab plus ipilimumab (N + I) demonstrated meaningful improvements in key patient-reported outcomes, in patients with pretreated microsatellite instability-high (MSI-H) metastatic colorectal cancer (mCRC). We report a case of severe necrotizing myositis which occurred in a patient treated with N + I combination for mCRC MSI-H. A 61-year-old woman was diagnosed with mCRC MSI-H and BRAFV600E mutated with synchronous liver, pleural, and lymph nodes metastases. After she failed to respond to standard chemotherapy (two lines with 5-fluorouracil, oxaliplatin, and irinotecan + bevacizumab), she received in a clinical trial (CheckMate 142), nivolumab 3 mg/kg, and ipilumumab 1 mg/kg every 3 weeks [4]. One week after the second infusion, she developed rapidly extending proximal muscles weakness associated with diffuse erythematous rash with grade 2/5 strength on abdominal, dorsal, and proximal limb muscles and impressive muscular edema. The creatine kinase level was at 14827 U/L (0-160 U/L), without any detectable autoantibodies. The electromyogram showed a severe myogenic syndrome, and muscular histological analysis demonstrated extensive muscular necrosis, with scarce lymphocytic infiltrates and pathological expression of class I HLA and C5b9 complement deposits with severe endomysial edema. N-I therapy was discontinued. Intravenous methylprednisolone was initiated for 3 days followed by 1 mg/kg/day orally, combined with intravenous immunoglobulins (2 g/kg/day for 2 days). At 3 years of first infusion of N + I, patient is without any new progressive disease, in partial response on the liver, pleural, and nodes metastasis, with only persistent minor psoas weakness.