Molecular characterization of pediatric mastocytosis revealed different somatic mutations with uncertain prognostic value

Background: Mastocytosis is a rare clonal hematological neoplasm, characterized by cutaneous manifestations in children and categorized as: maculopapular cutaneous mastocytosis (MPCM), diffuse cutaneous mastocytosis (DCM) and mastocytoma. Systemic mastocytosis (SM) typically occurs in adults with c-KIT D816V mutation. Additional genetic mutations (TET2, NRAS, SF3B1, ASXL1, etc.) have been detected using Next-Generation Sequencing (NGS) in the adult population while limited information is available in the pediatric setting. Methods: 36 patients (pts) with pediatric mastocytosis diagnosed between 1997 and 2021 were included. Peripheral blood samples were collected to detect c-KIT D816V mutation, using both RT-PCR and ddPCR techniques, and to investigate other molecular mutations using NGS panel for rare and myeloid genes. Results: Median age of lesion onset was 4.7 months (range birth-17.8 years). 58% of the cohort underwent cutaneous biopsy after a median 3.77 months from lesion onset (range 2.49 months–11.6 years). 20 (55%) were classified as MPCM, 10 (28%) as DCM and 6 (17%) as mastocytoma. Median tryptase value at the onset was 5 ng/mL: MPCM (range 1.2–141 ng/mL) vs. DCM (range 2.71–19.4 ng/mL) vs. mastocytoma (range 3.8–7.3 ng/mL). Two MPCM pts developed indolent SM (ISM) after 10 and 20 years from the onset of disease. RT-PCR identified c-KIT D816V mutation in 4 pts (2 MPCM, 1 DCM, 1 ISM). NGS revealed the precedent mutation in 3 pts, c-KIT D816Y and c-KIT Y553C in 2 pts. An additional 10 myeloid gene mutations were detected by NGS: 5 already known (ASXL1 G1397S; JAK2 L393V; c-KIT D816Y; LNK E208Q; TET2 Y867H) and 5 not previously described (ETV6 A215P; c-KIT Y553C; NFE2 I291T; SH2B3 G382D; SH2B3 L438V). A single mutation was found in 7 pts (3 MPCM, 3 DCM, 1 ISM), while two or more mutations in 3 DCM pts. Overall, 9/36 pts (5 DCM, 3 MPCM, 1 mastocytoma) presented spontaneous complete regression of cutaneous lesions after a median time of 25 months (range 17 months–25 years). Conclusion: c-KIT mutations resulted in 35% of the children tested. The RT-PCR technique resulted more sensitive in finding c-KIT D816V, while NGS in detecting other mutations whose prognostic roles require further investigation.