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 = 12), osteosarcoma (n = 2), rhabdomyosarcoma (n = 2), leiomyosarcoma (n = 1) and malignant peripheral nerve sheath tumor (n = 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.