Prognostic impact of CD44 in patients with mastocytosis. (A-C) Probability of OS was determined for subgroups of patients with mastocytosis. Patients were split into subgroups based on higher (red curves) and lower expression (blue curves) levels of CD44 on CD117⁺⁺/CD34⁻ MCs (A), CD34⁺/CD38⁻ SCs (B), and CD34⁺/CD38⁺ PCs (C). Cutoff values of SIs to define higher and lower CD44 surface expression levels based on receiver-operating characteristic curve analyses were 19 for MCs, 20 for SCs, and 25 for PCs. The analyzed patient cohort (n = 56) consisted of 2 patients with CM, 20 with ISM, 22 with SM-AHN, 6 with ASM, and 6 with MCL. The median follow-up of our patients was 2.8 years. The probability of OS was calculated by the product limit method of Kaplan and Meier. The differences in OS in the subgroups defined by higher or lower surface expression of CD44 were significant by log-rank test. *P < .05. (D-E) The probability of OS (D) and PFS (E) was determined in 129 patients with mastocytosis, consisting of 15 with CM, 74 with ISM, 7 with SSM, 20 with SM-AHN, 9 with ASM, and 4 with MCL. Based on receiver-operating characteristic curve analysis, patients were split into those with higher levels (≥200 ng/mL) of sCD44 (red curves) or lower levels of sCD44 (<200 ng/mL) (blue curves). The median follow-up of our patients was 6.6 years. The probability of OS and PFS was calculated by the product limit method of Kaplan and Meier. The differences in OS and PFS in the subgroups defined by higher or lower levels of sCD44 were significant by log-rank test. *P < .05.