Ossifying fibromyxoid tumours with lipomatous and cartilaginous differentiation: A diagnostic pitfall

• Published in: Histopathology 2024-12
• Main Authors: Klubíčková, Natálie, Billings, Steven, Dermawan, Josephine K T, Molligan, Jeremy F, Fritchie, Karen
• Format: Article
• Language: English
• ISSN: 0309-0167; 1365-2559; 1365-2559
• DOI: 10.1111/his.15396

Ossifying fibromyxoid tumour is a rare mesenchymal neoplasm predominantly affecting adults characterised by a multinodular growth pattern and the presence of a fibrous pseudocapsule with areas of ossification. Prompted by the recognition of a non-ossifying ossifying fibromyxoid tumour with lipomatous differentiation which caused diagnostic difficulty, we sought to further explore cases of ossifying fibromyxoid tumour with non-osseous heterologous elements. A search of our institutional and consultation archives revealed three additional cases that demonstrated lipomatous components and two cases with cartilaginous differentiation. RNA-sequencing revealed fusions involving PHF1 (n = 4) or EPC1 (n = 1) in all (five of five) cases tested, including EPC1::PHC1 and JAZF1::PHF1 fusions, which have not been reported before in ossifying fibromyxoid tumour. These six cases expand the histomorphological spectrum of ossifying fibromyxoid tumour, introducing lipomatous differentiation as a hitherto undocumented feature. Awareness of these rare variants will ensure appropriate diagnosis and clinical management.