Immune checkpoint inhibitor-related myositis associated with atezolizumab therapy

Checkpoint inhibitor immunotherapy has revolutionized the treatment of metastatic cancer with new monoclonal antibodies exploiting novel therapeutic targets being developed at a rate commensurate with our increasing understanding of tumor immunobiology.
Atezolizumab is a humanized monoclonal antibody that binds to and inactivates programmed cell death ligand, a protein expressed on tumor cells which helps them avoid immune surveillance through binding to programmed cell death protein (PD-1) receptors on cytotoxic T-cells and thereby suppressing their activity.

Reactivating the antitumor immune response with atezolizumab can, however, result in the development of a range of immune-mediated treatment-related side effects, and a variety of nervous system disorders including peripheral neuropathy and myasthenia gravis have been described. Although the immune checkpoint inhibitors nivolumab and pembrolizumab that target PD-1 have been implicated in autoimmune myositis, this adverse event has not been well reported in atezolizumab, with only case previously described in the literature.