Primary (De Novo) Dedifferentiated Liposarcoma in the Extremities: A Multi-Institution Tohoku Musculoskeletal Tumor Society Study of 18 Cases in Northern Japan

Objective: Dedifferentiated liposarcomas usually occur in the retroperitoneal space and relatively rarely in the extremities. Methods: We identified 18 patients with primary dedifferentiated liposarcoma in the extremities from the files of Tohoku Musculoskeletal Tumor Society and analyzed demographics, histologic findings, treatments and prognostic factors. The average follow-up period was 58 months. Results: The subjects were 12 men and 6 women with a mean age of 65 years. All tumors were in the thigh. Nine patients noticed a rapid enlargement of the long-standing tumor. Histologic subtypes of the dedifferentiated area were undifferentiated pleomorphic sarcoma (n ¼ 12), osteosarcoma (n ¼ 2), rhabdomyosarcoma (n ¼ 2), leiomyosarcoma (n ¼ 1) and malignant peripheral nerve sheath tumor (n ¼ 1). In the patient with rhabdomyosarcoma-like dedifferentiated area, extensive necrosis was observed after the preoperative chemotherapy. One patient who underwent marginal excision developed a local recurrence, but inadequate surgical margin was not associated with a risk of local recurrence. Three patients had lung metastasis at initial presentation, and four other patients developed lung metastases during the follow-up period. The overall survival rate was 61.1% at 5 years. On univariate analyses, large size of the dedifferentiated area (.8 cm), high MIB-1-labeling index (.30%) for the dedifferentiated area and lung metastasis at initial presentation were significantly associated with poor prognosis. Conclusions: Primary dedifferentiated liposarcoma in the extremities predominantly occurred in the thigh and a rapid enlargement of long-standing tumors was a characteristic symptom. Although the local behavior of these tumors was less aggressive than that of retroperitoneal dedifferentiated liposarcomas, they had a relatively high metastatic potential.