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

Javier I. Muñoz-González, Iván Álvarez-Twose, María Jara-Acevedo, Ana Henriques, Esther Viñas, Carlos Prieto, Laura Sánchez-Muñoz, Carolina Caldas, Andrea Mayado, Almudena Matito, Noelia Dasilva-Freire, Alberto Orfao and Andrés C. García-Montero

Key Points

  • D816V KIT allele frequency in BM, higher sβ2M levels, and A/R/D pathogenic mutations identify ISM cases at very high risk for progression.

  • Pathogenic mutations in the A/R/D genes identify ISM cases with multilineal KIT and poorer prognosis.

Abstract

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 β2-microglobulin (sβ2M) 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.

  • Submitted November 19, 2018.
  • Accepted May 23, 2019.
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