Aberrant expression of CD2, CD25, and/or CD30 on mast cells is a minor diagnostic criterion of SM and if present, suggests a diagnosis of SM (Valent, Akin, et al., 2007; Valent, Akin, Hartmann, et al., 2017; Valent, Akin, & Metcalfe, 2017). The gene discussed is CD2; the disease is systemic mastocytosis.