The First Report of BRAF V600E Mutation in Paratesticular Mesothelioma

Paratesticular mesothelioma is rare with limited data on its clinicopathologic and molecular characteristics. BRAF p.V600E mutation is exceptionally rare in mesotheliomas and has been reported in 5 pleural mesotheliomas to date. Herein, we reported the first paratesticular mesothelioma harboring a BRAF V600E mutation. A 44-year-old man with a history of asbestos exposure presented with painless right testicular swelling. Orchiectomy revealed a 1.5-cm biphasic mesothelioma composed of 80% sarcomatoid component admixed with 20% epithelioid component. The sarcomatoid component consisted of spindle cells in fascicular to haphazard patterns within a myxoid to collagenous stroma, while the epithelioid component showed predominantly tubulopapillary architecture. The biphasic mesothelioma expressed mesothelial markers with intact expression of BAP1, MTAP, and Merlin. Next-generation sequencing identified BRAF V600E mutation, which was also confirmed by immunohistochemistry for BRAF V600E. The patient received adjuvant chemotherapy and remained free of disease at 11 months of follow-up. This report expands the histomorphologic and molecular spectrum of paratesticular mesothelioma with the novel identification of a BRAF V600E mutation.