Clinicopathological features and differential diagnosis of a case report of atypical spindle cell/pleomorphic lipomatous tumor

Abstract

Atypical spindle cell/pleomorphic lipomatous tumor (ASPLT) is a rare, benign adipocytic neoplasm characterized by a highly indolent biological behavior and a lack of distant metastatic potential. We present a 44-year-old male with a continuously enlarging, mildly tender right back mass. Magnetic resonance imaging showed a large subcutaneous tumor, subsequently treated with extended surgical excision. Histopathology revealed atypical spindle cells, adipocytes, lipoblasts, and floret-like multinucleated giant cells. Immunohistochemistry demonstrated a notable loss of retinoblastoma protein (RB1) expression. Crucially, fluorescence in situ hybridization (FISH) confirmed the absence of murine double minute 2 (MDM2) gene amplification, establishing the definitive diagnosis. The patient experienced no recurrence or metastasis during an 18-month follow-up. The key lesson for physicians is the critical need to integrate histomorphology, immunohistochemistry, and molecular genetic testing-specifically FISH-to accurately differentiate this benign entity from well-differentiated liposarcoma, thereby preventing unnecessarily aggressive treatments.