Table 1.

SM criteria

Major SM criterion	Multifocal dense infiltrates of MCs (≥15 MCs in aggregates) in BM biopsies and/or in sections of other extracutaneous organ(s)
Minor SM criteria	a. >25% of all MCs are atypical cells (type I or type II) on BM smears or are spindle-shaped in MC infiltrates detected on sections of visceral organs
	b. KIT point mutation at codon 816 in the BM or another extracutaneous organ
	c. MCs in BM or blood or another extracutaneous organ exhibit CD2 and/or CD25
	d. Baseline serum tryptase level >20 ng/mL (in case of an unrelated myeloid neoplasm, item d is not valid as an SM criterion)
If at least 1 major and 1 minor or 3 minor SM criteria are fulfilled, the diagnosis of SM can be established

SM criteria were defined by the WHO in 2001 and have been confirmed in the WHO updates of 2008 and 2016.