Diffuse nuclear immunoreactivity for FOSB (>50% of cells) was observed in 48 of 50 (96%) pseudomyogenic hemangioendotheliomas and 13 of 24 (54%) epithelioid hemangiomas (including all angiolymphoid hyperplasia with eosinophilia type).
Although FOSB-rearranged EH do not show significant morphologic overlap with SERPINE1-FOSB fusion-positive pseudomyogenic hemangioendothelioma, FOSB oncogenic activation is emerging as an important event in these benign and intermediate groups of vascular tumors.