Disseminated Xanthogranuloma Harboring a GAB2::BRAF Fusion and MITF Pathogenic Variant Successfully Treated With Cobimetinib

Several activating mutations and gene fusions involving the mitogen-activated protein kinase (MAPK) pathway have appeared in the literature regarding histiocytic neoplasms. We identified a GAB2::BRAF fusion in a cutaneous lesion of a 36-year-old male who developed central diabetes insipidus and reddish-pink grouped papules on the bilateral axillary rims, inguinal region, and periocular skin. Skin biopsy obtained from an axillary lesion showed a CD68+, S100-, and CD1a- histiocytic proliferation with foamy histiocytes and multinucleated Touton giant cells, compatible with xanthogranuloma. Next-generation sequencing identified a GAB2::BRAF fusion involving Exon 2 of GAB2 and Exon 10 of BRAF. Our case further highlights this novel fusion in the MAPK signaling pathway as a possible driver of nonLangerhans cell histiocytosis (NLCH) and underscores the utility of performing molecular studies on skin biopsy specimens with NLCH to help identify potential targets for therapy.

Abstract from PubMed