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

Chondromyxoid fibroma (CMF) is a rare benign bone tumour. While CMF located entirely on the surface of a bone (i.e. juxtacortical CMF) has been well characterised, CMF has not so far been convincingly documented to arise in soft tissues 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 novel PNISR::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 a GRM1 gene fusion or GRM1 expression by immunohistochemistry

A unique case of multicentric infantile myofibromatosis with radiologic-pathologic correlation

Infantile myofibromatosis (IM) is a rare condition with a variable clinical presentation that characteristically affects young children. Most frequently it presents as one or more benign nodules of the skin, bones, soft tissues, or, rarely, visceral organs. According to the location and number of lesions, there are three different forms: solitary, multicentric without visceral involvement, and multicentric with visceral involvement (generalised), with the latter having the least favourable prognosis. We present a unique case of severe congenital generalised IM in a new-born male who required intubation and mechanical ventilation immediately after the birth due to respiratory distress. A chest radiograph showed numerous tumours involving the entire lung, resembling a metastatic lung disease. Additionally, the neonate had multiple, bluish, papular skin nodules and a biopsy of a skin nodule ultimately led to the diagnosis of IM. Diffuse lung involvement prevented adequate ventilation which resulted in multiorgan failure and death before targeted treatment could have been initiated. The presented case is unique, as such atypical extensive involvement of the lung and leptomeninges in IM has not been reported before. In this brief report, we present the findings of radiographic and ultrasonographic examinations in correlation with autopsy and histopathology