[Clinical and histopathological features of immune checkpoint inhibitor-related myositis in patients with advanced non-small cell lung cancer].

To investigate the clinicopathologic features and outcome of myositis in patients with advanced non-small cell lung cancer treated with immune checkpoint inhibitors. The patients diagnosed with immune checkpoint inhibitor-related (ICI) myositis in the database of Respiratory Pathology Center of The First Affiliated Hospital, Guangzhou Medical University from June 2019 to December 2020 were retrospectively analyzed. We reported the muscle histology and main clinical manifestations of the patients in this study. Seven patients with advanced non-small cell lung cancer and ICI related myositis were examined; all of the patients were male, with a median age of 64 (range 42-79) years. All seven patients developed myositis under therapy (three for pembrolizumab, three for sintilimab, and one for camrelizumab). Median delay between ICI initiation and myositis onset was 45 (range 15-176) days. Clinical manifestations were dominated by acute or subacute myalgia and limb weakness. Four patients had evidence of myocarditis. In all of the 7 patients, creatine kinase levels were elevated (median 2 354.4, range 468.6-19 709.2 U/L), while myositis-associated antibodies Ro-52 were positive in four patients. Muscle biopsy showed evident multifocal necrotic myofibers and infiltration of inflammation in two patients. Other patients only showed non-specific endomysial inflammation. Infiltration of inflammation mainly consisted of CD8 T cells and CD68 histocytes. After the identification of ICI related myositis, ICI treatment was withdrawn in all patients; 6 patients received corticosteroids therapy. All patients had shown marked clinical improvement. ICI myositis presents with remarkably homogeneous and unique clinicopathologic features, and half of the patients exhibit heightened risk for adverse cardiovascular events, which can be life-threatening if not treated in time. Timely identification of these patients, ICI withdrawal and rapid initiation of corticosteroids therapy can significantly improve patient outcome and/or save patients' lives.