Detection of CD44 on the surface of neoplastic cells and in the sera of patients with mastocytosis. (A) BM cells obtained from controls (Co; patients with lymphoproliferative neoplasms or normal/reactive BM, n = 44) and patients with CM (n = 2), ISM (n = 20), SM-AHN (n = 22), ASM (n = 6), or MCL (n = 6) were analyzed by multicolor flow cytometry. Expression of CD44 on CD45⁺/CD117⁺⁺/CD34⁻ MCs is expressed as SI (MFI produced by CD44 antibody/MFI of the isotype-control antibody). (B-C) CD44 expression on CD34⁺/CD38⁻ SCs (B) and CD34⁺/CD38⁺ PCs (C) was analyzed in BM samples of controls (Co; patients with lymphoproliferative neoplasms or normal/reactive BM, n = 55) and patients with CM (n = 2), ISM (n = 20), SM-AHN (n = 21), ASM (n = 6), or MCL (n = 6) by multicolor flow cytometry and is expressed as SI. Results are shown as boxplots (Tukey) and represent median values (black horizontal lines), the 25th to 75th percentiles (gray boxes), ranges (whiskers), and outliers (black dots). *P < .05 compared with control (Dunn’s multiple comparisons test). As visible, MCs, SCs, and PCs expressed higher levels of CD44 in advanced SM compared with CM or controls. (D) sCD44 (ng/mL) in the sera of healthy controls (Co; n = 15) or patients with CM (n = 15), ISM (n = 74), SSM (n = 7), SM-AHN (n = 20), ASM (n = 9), or MCL (n = 4) was measured by ELISA. Results are shown as boxplots (Tukey) and represent median values (black horizontal bars), the 25th to 75th percentiles (gray boxes), ranges (whiskers), and outliers (black dots). *P < .05 compared with control, CM, or ISM (Dunn’s multiple comparisons test). As visible, sCD44 levels in advanced SM were higher compared with ISM, CM, or healthy controls. (E) sCD44 (ng/mL) and serum tryptase (ng/mL) were measured over 52.3 months in the sera of a 21-year-old male patient with KIT D816V-negative ASM (patient 149 in supplemental Table 1). Initially, the patient received prednisolone (50 mg/day) and interferon-α (IFN-α) (3 × 10⁶ international units every second day). Because of resistance, the patient then received 3 cycles of cladribine (2CdA) (0.14 mg/kg, days 1-5) combined with prednisolone (12.5 mg/day). Despite therapy, the patient progressed to MCL. After progression to MCL (KIT D816V negative), the patient first received imatinib (400 mg/day) and prednisolone (25 mg/day), which was followed by a transient decrease in tryptase and sCD44 levels. However, no major response was achieved and the patient was then treated with induction polychemotherapy (CT) consisting of daunorubicin (45 mg/m², days 1-3), etoposide (100 mg/m², days 1-5), and cytarabine (2 × 100 mg/m², days 1-7), (DAV 3+5+7 protocol). However, despite a short-lived response, the patient died 3.2 months after progression to MCL. sCD44 and tryptase levels decreased after induction polychemotherapy and increased with disease progression.