Giant Atypical Spindle Cell Lipomatous Tumor of Retroperitoneal Origin Presenting with Lung Metastasis and Extension to the Thigh: A Case Report with Literature Review

Abstract Retroperitoneal liposarcomas are rare, and their variants, atypical spindle cell lipomatous tumor (ASCLT), are rarer. Though ASCLTs are benign, they have high recurrence despite complete surgical excision. We present a rare case of a 22-year-old male presented with insidious-onset, and gradually progressive swelling over left inguinofemoral, and iliac fossa region. Also, the patients had a history of weight loss, pricking-type pain radiating to left lower limb, and breathlessness on exertion. Contrast-enhanced computed tomography (CECT) abdomen revealed a large well-defined heterogeneously enhancing soft mass located in pelvis, and involving left-sided iliopsoas muscle suggestive of retroperitoneal soft tissue sarcoma and CECT thorax showed metastasis. The CT-guided core biopsy led to the definitive diagnosis of low-grade ASCLT. Subsequently, the patient was initiated on concurrent neoadjuvant chemoradiotherapy followed by complete surgical excision. The findings in this report make it critical to enhance our understanding of this rare tumor, with surgery being the best treatment option.