The diagnosis of SM is based on WHO criteria, including abnormal histopathological and cytological aspects of MC in the bone marrow (BM) or in other internal organs, an elevated basal serum tryptase (BST) level, an aberrant immunophenotype of MC (CD2+/CD25+), and/or identification of the somatic mutation (pathogenic variant) KIT p.D816V [9,10,11]. This evidence concerns the gene KIT and systemic mastocytosis.