Introduction: Myxoid liposarcoma (MLPS) is a rare soft tissue sarcoma comprising 5–10% of adult cases, most often in the thigh. Diagnosis is challenging due to nonspecific imaging findings and resemblance to benign lesions. Case Report: A 42-year-old male presented with a painless, enlarging upper right medial thigh mass. CT and ultrasound suggested a complex solid lesion, possibly benign. Outpatient surgical excision revealed a red, gelatinous, non-encapsulated mass. Frozen section suggested a myxomatous spindle cell tumor. Final pathology confirmed MLPS FNCLCC grade 2 (intermediate grade) with DDIT3 rearrangement on fluorescence in situ hybridization (FISH). Margins were negative but close. Postoperative PET scan and Signatera MRD assay were negative for metastasis. Given the tumor’s size (>10 cm) and known radiosensitivity, adjuvant radiotherapy (60–66 Gy) was initiated. Discussion: MLPS features myxoid stroma, plexiform vasculature, and, in high-grade tumors, a round cell component. The FUS::DDIT3 fusion gene is diagnostic. While MRI offers superior soft tissue characterization, definitive diagnosis requires pathology and molecular testing. Surgical excision with negative margins remains standard, with radiotherapy recommended for large tumors or close margins to reduce recurrence. This case highlights the limitations of preoperative imaging and the value of intraoperative pathology in guiding management. Conclusions: Early recognition, accurate diagnosis, and tailored multimodal treatment are essential for MLPS. Given the potential for recurrence, late extrapulmonary metastases, long-term surveillance with imaging, and molecular assays are critical for optimizing outcomes.
Correa et al. (Mon,) studied this question.