Kinase expression in angiomatoid fibrous histiocytoma: panTRK is commonly expressed in the absence ofNTRKrearrangement

Abstract

Angiomatoid fibrous histiocytoma (AFH) is a soft tissue tumour of intermediate (rarely metastasising) malignant potential, which harboursEWSR1/FUSgene fusions. These tumours can express anaplastic lymphoma kinase (ALK) in the absence of gene rearrangement or copy number alteration and can also coexpresses Pan-TRK immunohistochemistry (IHC). AllEWSR1/FUS-rearranged AFH were retrieved from the files of three institutions and Pan-TRK (EPR17341), ALK and BRAF V600E IHC were performed. Fourteen AFH cases were identified, which included three cases of intracranial mesenchymal tumours with FET-CREB fusions. PanTRK and ALK positive immunostaining was identified in 9 (64.2%) and 12 (85.7%) cases, respectively. NoNTRKorALKtranslocations or increased copy number/amplification were identified in all eight cases which had fluorescence in situ hybridisation and/or next generation sequencing forNTRK1-3andALKavailable for assessment. None of the cases expressed BRAF-V600E.Although our study is limited, our report is the first to document PanTRK expression in AFH in the absence of identifiableNTRK1-3gene alterations.