IntroductionImmune checkpoint inhibitors (ICIs) are approved for the management of solid and hematologic malignancies and have significantly improved cancer-related care. ICIs augment the intrinsic immunity through various mechanisms including targeting programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), and ligand proteins on tumor cells. The combined effects of ICIs block the inhibition of T-cells and allow them to kill cancer cells. Although significant antitumor efficacy has been reported, a wide range of life-threatening inflammatory and autoimmune side effects have been associated with ICIs [1].ICI-induced myocarditis with myositis/myasthenia gravis overlap syndrome is a rare adverse effect of ICI therapy and carries a high mortality [2]. Antibodies are used in diagnostics and the disease is known to confer pathogenicity through certain molecular targets: acetylcholine receptor antibody [3], muscle-specific receptor tyrosine kinase [4], and numerous extracellular and intracellular antibodies [5]. However, 10-15% of patients with ICI-induced myasthenia gravis may be seronegative and antibody detection has proven invaluable in measuring disease severity in patients with myasthenia gravis [6]. Ultimately, the diagnosis is clinical while novel antigenic targets and their diagnostic relevance continues to be studied. We present two cases of ICI-induced myocarditis with myositis/myasthenia gravis overlap syndrome and review current literature to emphasize its severity and management.