Immune checkpoint inhibitor–related myositis and myocarditis in patients with cancer

Objective: To report the clinicopathological features and outcome of myositis in patients treated with immune checkpoint inhibitors (irMyositis). Methods: We retrospectively analyzed patients diagnosed with irMyositis in tertiary centers in Paris, France, and Berlin, Germany, from January 2015, to July 2017. Main outcomes were clinical manifestations and muscle histology, which included MHC-I, C5b-9, CD3, CD4, CD8, CD20, CD68, PD-1, PD-L1 and PD-L2 immunohistochemical stains. Results: Ten patients with metastatic cancer were included; median age was 73 years (range, 56-87). Median follow-up duration was 48 weeks (range 16-88). Six patients developed myositis during nivolumab therapy, one during pembrolizumab, one during durvalumab, and two during combined nivolumab and ipilimumab. Median delay between immune checkpoint inhibitor (ICI) initiation and myositis onset was 25 days (range, 5-87). Clinical manifestations were dominated by acute or subacute myalgia (8 patients), limb-girdle (...