(P 498) DEDIFFERENTIATED LIPOSARCOMA OF THE EXTREMITIES: CHARACTERISTICS AND OUTCOME

Objective: Literature on dedifferentiated liposarcoma of the extremities (DDL-E) is rare and its features have not been clearly elucidated. In this study, we aimed to investigate the characteristics and the outcome of DDL-E.

Methods: Twenty-five patients diagnosed with DDL-E from July 2004 to December 2020 were analyzed retrospectively. Demographic characteristics, histopathologic findings, fatty composition on magnetic resonance imaging (MRI), and treatment methods were collected. Oncologic outcomes (local recurrence-free survival (LRFS), metastasis-free survival (MFS) and disease-specific survival (DSS)) and prognostic factors were analyzed.

Results: There were 16 men and 9 women. The median age was 65 years (range, 35-87). The most common site of involvement was the thigh (n=22). The mean tumor size was 11.1 centimeters (cm) (range, 2.8-22.8). Eight (32%) presented after unplanned excision and 4 (12%) had metastases at presentation. Two had non-pulmonary organs (pancreas, peritoneum) as the first target of metastasis. Two patients (8%) had documented transition from well-differentiated liposarcoma (WDL) into DDL after 2 and 10 years of follow-up. Tumors were diagnosed as DDL-E when they were positive for MDM2 or CDK4, even without a WDL component. Based on the spectrum of fatty composition on MRI, 6 patients (24%) had well- defined fatty mass juxtaposed to well-defined non-fatty mass (type I), 2 (8%) had focal non-fatty component within a large fatty mass (type II), 9 (36%) had focal fatty component within a large non-fatty mass (type III), and 8 (32%) had non-fatty mass (type IV). As for FNCLCC grading, there were 2, 18, and 2 patients in grade 1, grade 2, and grade 3, respectively. Eleven patients underwent postoperative radiotherapy while two had postoperative chemotherapy. Histologically negative margin was achieved in 19 patients (73%).
Five patients (20%) had local recurrence and 5-year LRFS was 82.5%. In all, 7 patients (20%) had metastases. Of the 23 patients without initial metastases, 3 (12%) developed metastasis, and 5-year MFS was 92%. One patients (4%) died of disease at 2 months. Five year DSS was 96%. Local recurrence was associated with positive surgical margin (p=.012). DSS was associated with metastases (p=0.006). Fatty composition on MRI, tumors size or FNCLCC grade was not associated with oncologic outcome.

Conclusion: DDL-E without initial metastasis has a favorable oncologic outcome. Non-pulmonary organs are common first target of metastasis in DDL-E. Achieving negative surgical margin seems important for local control. Fatty composition on MRI, tumors size or FNCLCC grade was not associated with oncologic outcome.