Identification of KIT activating mutations in paediatric solitary mastocytoma

Mastocytosis is an abnormal mast cell proliferation involving one or more organs, in particular the skin and bone marrow. In children, disease is usually limited to the skin, with three distinct clinical presentations: urticaria pigmentosa, diffuse cutaneous mastocytosis and solitary mastocytoma. Although the KIT D816V mutation is typically found in adult-onset mastocytosis, it is less commonly seen in childhood-onset mastocytosis, and the frequency of KIT mutations in paediatric solitary mastocytoma is poorly documented.

In this study we analysed KIT exons 8, 9, 11, 13 and 17 in nine cases of paediatric solitary mastocytoma using a laboratory-developed Sanger sequencing assay. A KIT mutation was identified in six cases (67%), including three with the D816V mutation typical of adult-onset disease, and another three with an internal tandem duplication (p.A502_Y503dup) in exon 9, previously described in gastrointestinal stromal tumour.

Paediatric solitary mastocytoma is frequently associated with KIT activating mutations, in keeping with a clonal process. KIT mutational status appears insufficient to explain the divergent biology of childhood and adult-onset disease.