Immune checkpoint inhibitors (ICI) are active in multiple cancers. Their main drawback is the incidence of immune related adverse events; among which ICI-myocarditis (ICIM) is rare but can be the most life-threatening (up to 50% lethal). ICIM is due to ICI unleashing cytotoxic auto-reactive T-cells recognizing a culprit target antigen located on muscles and destroying them. Most often, ICIM occurs within a systemic ICI-myotoxicity, with peripheral muscular involvement (ICI-myositis), mimicking eventually myasthenia-gravis syndrome. Human Leukocyte Antigen (HLA) are cell surface proteins key for the regulation of the immune system acting via presentation of culprit antigens by antigen presenting cells (macrophages) to T-cells, subsequently triggering the destruction/tolerance of cells carrying this antigen. The HLA system (chromosome 6) is the most polymorphic region in the human genome and is associated with auto-immunity including myocarditis. HLA class I alleles have been strongly associated with some T-cell-mediated drug hypersensitivity reactions with handful patients needed to be tested to prevent a single case, leading to globally required cost-effective HLA typing pre-prescription for some drugs.