According to 2008 World Health Organization diagnosis criteria,[1] to diagnose SM requires either the major criteria of multifocal dense infiltrations of mast cells in extracutaneous organs (more than 15 mast cells aggregating) with 1 of 4 minor criteria (more than 25% mast cells in extracutaneous organs show an abnormal morphology; codon 816 KIT mutation D816V detected in extracutaneous organs; mast cells in bone marrow express CD2, CD25 or both; more than 20 ng/mL serum tryptase) or 3 minor criteria. Here, KIT is linked to systemic mastocytosis.