Expanding the molecular signatures of malignant ossifying fibromyxoid tumors with two novel gene fusions: PHF1::FOXR1 and PHF1::FOXR2.

Ossifying fibromyxoid tumor (OFMT) is a rare enigmatic tumor of uncertain differentiation that can be classified as typical, atypical, and malignant subtypes based on cellularity, nuclear grade, and mitotic activity. The majority of OFMTs, regardless of the risk of malignancy, harbor genetic translocations. Herein, we report two cases of malignant OFMT, including one with evidence of dedifferentiation, harboring novel PHF1::FOXR1 and PHF1::FOXR2 gene fusions. In keeping with previously reported tendencies of OFMTs with rare variant fusions, these tumors also demonstrated malignant behavior, unusual morphology, and non-specific immunophenotypes.