247 Myxoid Dermatofibrosarcoma Protuberans with Giant Cell Fibroblastoma-like Features

Introduction/Objective Dermatofibrosarcoma protuberans (DFSP) is a rare, low-grade cutaneous sarcoma with a high local recurrence rate but low metastatic potential. The myxoid variant of DFSP is exceptionally rare, and its co-occurrence with giant cell fibroblastoma (GCF), particularly in adults, presents significant diagnostic challenges. DFSP is characterized by the t(17;22)(q22;q13) translocation, resulting in the COL1A1-PDGFB fusion gene, which drives tumorigenesis. Myxoid DFSP is distinguished by its abundant myxoid stroma, often obscuring the typical storiform pattern, while GCF features multinucleated giant cells and pseudovascular spaces. The coexistence of these entities in adults is exceedingly rare, necessitating a diagnostic approach integrating histopathology, immunohistochemistry, and molecular studies. Methods/Case Report A 32-year-old male presented with a slowly enlarging, protuberant mass on his left upper thigh/groin region, which had been present for several months. The patient had a history of a similar lesion excised two years prior. Physical examination revealed a 3 cm firm, nodular mass with slight ulceration. Histopathological examination showed a dermal-based proliferation of spindle and stellate cells within a myxoid stroma, with scattered multinucleated giant cells and minimal nuclear atypia. Immunohistochemistry demonstrated diffuse CD34 positivity, while FISH analysis confirmed a PDGFB rearrangement, supporting the diagnosis of myxoid DFSP with GCF-like features. The patient underwent wide re-excision, but the deep margin showed potential tumor involvement, prompting further evaluation. Routine surveillance was advised due to the low metastatic potential of DFSP. Results NA Conclusion The myxoid variant of DFSP poses diagnostic challenges due to its histologic overlap with other myxoid neoplasms, such as superficial angiomyxoma, myxoid solitary fibrous tumor, and low-grade myxofibrosarcoma. Key distinguishing features include CD34 positivity, the COL1A1-PDGFB fusion gene, and the classic honeycomb infiltration pattern. The presence of GCF-like features in this case further complicates the diagnosis, as GCF is typically seen in children and is rare in adults. DFSP and GCF share a close histopathologic and molecular relationship, suggesting they represent different morphologic expressions of the same neoplastic process. Wide surgical excision with negative margins remains the gold standard for treatment, with Mohs micrographic surgery as an alternative for anatomically challenging locations. Tyrosine kinase inhibitors, such as imatinib, are effective for locally advanced or inoperable DFSP, particularly in tumors with the COL1A1-PDGFB fusion gene. Long-term follow-up is essential due to the high local recurrence rate. This case highlights the importance of integrating histopathologic, immunohistochemical, and molecular analyses for accurate diagnosis and optimal management of rare myxoid DFSP with GCF-like features.