Frequency and prognostic impact of KIT and other genetic variants in indolent systemic mastocytosis.

Indolent systemic mastocytosis (ISM) patients have a normal life expectancy, except in the 5% to 10% of cases that progress to more advanced SM (advSM), which has a significantly poorer outcome. Mutations in genes other than KIT frequently found in myeloid neoplasms have been associated with a poorer outcome among advSM, whereas limited information exists about their frequency and prognostic impact in ISM. We investigated the frequency and prognostic impact of variants in 18 genes, found to be altered in advSM, in 322 ISM patients (median follow-up, 5.7 years) divided into discovery (n = 200) and validation (n = 122) cohorts. Overall, 71 genetic variants were detected in 55 of 322 (17%) patients. Mutated ISM cases, particularly those carrying ASXL1, RUNX1, and/or DNMT3A (A/R/D) pathogenic variant allele frequencies (VAFs) ≥ 30%, exhibited significantly shortened (P < .001) progression-free survival (PFS) and overall survival (OS). Multivariate analysis showed that serum ß2-microglobulin (sß2M) levels > 2.5 µg/mL (hazard ratio [HR], 9.8; P = .001), together with a KIT D816V VAF ≥ 1% in bone marrow (BM) (HR, 10.1; P = .02) and pathogenic variants of A/R/D VAFs ≥ 30% (HR, 4.2; P = .02), were the best combination of independent predictors for PFS. In turn, A/R/D gene pathogenic VAF ≥ 30% was the only independent predictor for OS (HR, 51.8; P < .001). Based on these variables, 2 scoring systems were constructed for risk stratification of ISM at diagnosis with significantly different 10-year PFS (100%, 91%, 0% for scores of 0, 1, ≥2, respectively) and OS (100% and 50% for scores of 0 and 1) rates.

Bone Marrow Mast Cell Antibody-Targetable Cell Surface Protein Expression Profiles in Systemic Mastocytosis.

Despite recent therapeutic advances, systemic mastocytosis (SM) remains an incurable disease due to limited complete remission (CR) rates even after novel therapies. To date, no study has evaluated the expression on SM bone marrow mast cells (BMMC) of large panel of cell surface suitable for antibody-targeted therapy. In this study, we analyzed the expression profile of six cell-surface proteins for which antibody-based therapies are available, on BMMC from 166 SM patients vs. 40 controls. Overall, variable patterns of expression for the markers evaluated were observed among SM BMMC. Thus, CD22, CD30, and CD123, while expressed on BMMC from patients within every subtype of SM, showed highly variable patterns with a significant fraction of negative cases among advanced SM (aggressive SM (ASM), ASM with an associated clonal non-MC lineage disease (ASM-AHN) and MC leukemia (MCL)), 36%, 46%, and 39%, respectively. In turn, CD25 and FcεRI were found to be expressed in most cases (89% and 92%) in virtually all BMMC (median: 92% and 95%) from both indolent and advanced SM, but with lower/absent levels in a significant fraction of MC leukemia (MCL) and both in MCL and well-differentiated SM (WDSM) patients, respectively. In contrast, CD33 was the only marker expressed on all BMMC from every SM patient. Thus, CD33 emerges as the best potentially targetable cell-surface membrane marker in SM, particularly in advanced SM.

Impact of somatic and germline mutations on the outcome of systemic mastocytosis.

Systemic mastocytosis (SM) is a highly heterogeneous disease with indolent and aggressive forms, with the mechanisms leading to malignant transformation still remaining to be elucidated. Here, we investigated the presence and frequency of genetic variants in 34 SM patients with multilineal KIT D816V mutations. Initial screening was performed by targeted sequencing of 410 genes in DNA extracted from purified bone marrow cells and hair from 12 patients with nonadvanced SM and 8 patients with advanced SM, followed by whole-genome sequencing (WGS) in 4 cases. Somatic mutations were further investigated in another 14 patients with advanced SM. Despite the fact that no common mutation other than KIT D816V was found in WGS analyses, targeted next-generation sequencing identified 67 nonsynonymous genetic variants involving 39 genes. Half of the mutations were somatic (mostly multilineal), whereas the other half were germline variants. The presence of ≥1 multilineal somatic mutation involving genes other than KIT D816V, ≥3 germline variants, and ≥1 multilineal mutation in the SRSF2, ASXL1, RUNX1, and/or EZH2 genes (S/A/R/E genes), in addition to skin lesions, splenomegaly, thrombocytopenia, low hemoglobin levels, and increased alkaline phosphatase and ß2-microglobulin serum levels, were associated with a poorer patient outcome. However, the presence of ≥1 multilineal mutation, particularly involving S/A/R/E genes, was the only independent predictor for progression-free survival and overall survival in our cohort.