Tocilizumab is an IL-6R monoclonal antibody, which is currently used mainly for the management of rheumatoid arthritis, and nowadays, with an increase of its use for pathologies associated with CSS such as hemophagocytic lymphohistiocytosis, macrophage activation syndrome, or chimeric antigen receptor (CAR)-T cell therapy adverse reactions [10,13]. This evidence concerns the gene IL6R and macrophage activation syndrome.