Paediatric mastocytosis: long-term follow-up of 53 patients with whole sequencing of KIT. A prospective study.

BACKGROUND

Mastocytosis is a heterogeneous group of clinical disorders characterized by the abnormal accumulation of mast cells. The adult and paediatric forms differ in their clinical and genetic features and outcomes.

OBJECTIVES

To describe the clinical evolution of a well-characterized cohort of paediatric mastocytosis (PM), and to analyse the relationship between KIT mutation and the clinical course.

METHODS

This was a prospective cohort study performed at the National Clinical Reference Center for Mastocytosis. Diagnosis was confirmed by identification of KIT mutation on lesional skin biopsy. Mastocytosis subtype, mast cell mediator-related symptoms (MC MRS) and clinical course were recorded. Fifty-three patients with PM and > 4 years of disease course were enrolled. The mean ± SD age at the final evaluation was 13·2 ± 4·8 years. The main outcome was the type of KIT mutation as a predictor of evolution and clinical characteristics.

RESULTS

Patients presented with maculopapular cutaneous mastocytosis (n = 44), diffuse cutaneous mastocytosis (n = 6) or mastocytoma (n = 3). The mean duration of disease was 12·1 years. Substantial or partial cutaneous regression (18 of 53 and 16 of 53), stabilization or aggravation (16 of 53) and complete cutaneous regression (three of 53) were noted. MC MRS mainly regressed (21 of 53). For 22 patients, evolution of MC MRS and evolution of cutaneous lesions were different. No significant association between evolution and KIT mutation or between evolution and type of cutaneous mastocytosis was found. A late onset of the disease (after 2 years) is associated with worse evolution.

CONCLUSIONS

PM is not systematically self-regressive. MC MRS manifestations and cutaneous lesions can persist or increase overtime. KIT mutation is not a predictor of evolution.