CD274 and myositis disease: As for ICI-related myositis, classic myositis-specific antibodies do not represent a reliable tool to confirm or exclude the diagnosis as they are often negative, but muscle biopsies demonstrating endomysial infiltration of CD68 + cells expressing PD-L1 and CD8 + lymphocytes expressing PD-1 as well as sarcolemmal upregulation of MHC-1 may help orienting the diagnosis [54].