Subcutaneous chondromyxoid fibroma with a novel PNISR::GRM1 fusion —report of a primary soft tissue tumour without connection to an underlying bone

We report a subcutaneous CMF in a 34-year-old male, located on the distal medial aspect of the right thigh without any connection with the femur. The tumour measured 15  mm, it was well-circumscribed and displayed typical morphological features of a CMF. At the periphery, there was a small area of metaplastic bone. Immunohistochemically, the tumour cells were diffusely positive for smooth muscle actin and GRM1, and negative for S100 protein, desmin and cytokeratin AE1AE3. Whole transcriptome sequencing revealed a novelPNISR::GRM1 gene fusion.Our case indicates that CMF should be included in the differential diagnosis of soft tissue (including subcutaneous) tumours composed of spindle/ovoid cells, with a lobular architecture and chondromyxoid matrix. The diagnosis of CMF arising in soft tissues can be confirmed by identifying aGRM1 gene fusion or GRM1 expression by immunohistochemistry.

Source: Virchows Archiv - February 21, 2023 Category: Pathology Source Type: research