A rare case of cellular angiofibroma with sarcomatous transformation occurred in the popliteal fossa.

backgroundCellular angiofibroma (CAF) represents a rare, benign mesenchymal neoplasm. Histologically, it is characterized by a spindle-cell component closely resembling spindle-cell lipoma and an abundance of thick-walled blood vessels. This tumor predominantly arising in the vulvovaginal region of females and the inguinoscrotal region of males. It is commonly associated with a specific genetic deletion of the RB1 gene, which is mapped to the 13q14 locus on chromosome 13. Although rare, cases of CAF demonstrating morphological atypia or undergoing sarcomatous transformation (CAS) have been reported. However, CAS occurring in the popliteal fossa has not been previously reported. CASE PRESENTATION: In this study, we reported the first case of CAS in the popliteal fossa. A 60-year-old male patient presented with a two-year clinical history of a progressively enlarging mass on the posterior knee of his left lower limb. The tumor, located within the subcutaneous tissue, showed a distinct histological transition from classic CAF features to a sarcomatous component. This sarcomatous component exhibited distinct nodular formations, possessing histological characteristics analogous to those of atypical lipomatous tumor (ALT) and undifferentiated pleomorphic sarcoma (UPS). Immunohistochemical analysis identified diffuse p16 expression within atypical cells and sarcomatous regions, while demonstrating an absence of MDM2 or CDK4 expression. Next-generation sequencing (NGS) using a comprehensive 665-gene panel demonstrated the deletions in both the RB1 and TP53 genes, without evidence of MDM2 gene amplification. The patient experienced two postoperative recurrences. Adjuvant chemotherapy and radiotherapy were administered following the second surgical resection.

conclusionThis report highlights a rare and extraordinary case of CAS identified in the popliteal fossa. Through NGS, we had identified concurrent deletions of the RB1 and TP53 genes. Although the prognosis of this case was slightly worse than that reported in the literature, it provides additional evidence for expanding the known anatomical range of CAF.