Giant atypical lipomatous tumor/well-differentiated liposarcoma affects lower limb activity

RATIONALE: Liposarcomas are locally invasive mesenchymal soft tissue tumors; most deep liposarcomas are large. Liposarcomas have heterogeneous histomorphology, molecular and genetic characteristics, and clinical prognosis, making the diagnosis and treatment of giant liposarcomas difficult for bone tumor surgeons. PATIENT CONCERNS: A 70-year-old man presented with a mass in the posterior part of his left lower extremity that was first noticed 3 years prior. The mass was initially fist sized but continued to grow and had been affecting lower limb mobility on presentation. DIAGNOSES: Computed tomography and magnetic resonance imaging revealed a large space-occupying lesion in the left thigh muscles, which was identified as a low-grade malignant tumor. Postoperative pathology results confirmed the diagnosis of atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDLPS). INTERVENTIONS: The patient underwent open surgery to completely remove the tumor tissue and relieve pain. OUTCOMES: At the 10-month follow-up appointment, the patient had recovered well, function of the lower extremities had returned to normal, and no signs of recurrence or metastasis were noted. LESSONS: Although ALT/WDLPS is a locally invasive tumor with good prognosis, delayed treatment is associated with increased tumor size, which can affect lower limb mobility. Therefore, we believe that extensive surgical resection of tumor tissue is a suitable treatment for all ALT/WDLPS cases in order to avoid possible local recurrence. In addition, for ALT/WDLPS tumors that are difficult to extensively excise, long-term follow-ups are necessary due to the possibility of recurrence.