CD33 and systemic mastocytosis: Although CD33 was systematically expressed in all BMMC from SM patients (Table 2), among SM cases, BMMC from WDSM and ISMMC patients displayed greater levels of CD33 (expressed per cell) than ISMML patients (p = 0.01 and p = 0.05), ASM (p = 0.001 and p = 0.002), and MCL (p = 0.005 and p = 0.007) (Figure 1D).