(P 127) DEDIFFERENTIATED LIPOSARCOMA OF THE EXTREMITIES: A KOREAN MULTI-CENTER STUDY OF 107 CASES

Objective: Dedifferentiated liposarcoma of the extremities (DDL-E) is rare in comparison to that of the retroperitoneum. Its clinical features and surgical principle for resection margins at the dedifferentiated and well-differentiated components are yet to be elucidated. Our study aimed to evaluate 1) clinical characteristics, 2) oncologic outcomes (local recurrence, metastasis, and disease specific survival), and 3) prognostic factors of DDL-E.

Methods: This retrospective multi-center study examined patients diagnosed with DDL-E from August 2004 to May 2023 at 5 major sarcoma centers in South Korea. The diagnosis of DDL was made by pathologists based on the identification of transition from well-differentiated liposarcoma (WDL) to non-lipogenic sarcoma, or, in the absence of WDL component, nonlipogenic sarcoma with the amplification of MDM2 in immunohistochemistry or Fluorescence in situ hybridization .Clinical features, oncologic outcomes, and prognostic factors were analyzed.

Results: A total of 107 patients were reviewed. Median follow up was 36 (interquartile range 15.8-61) months. There were 143 males and 37 females. Median age was 64 (range 19-88). A total of 95 (88.8%) cases were de novo DDL, and 12 (11.2%) were secondary DDL. WDL was present in the MRI of 60 (56.1%) patients. Median tumor size was 10.5 cm (range 0.5–35).
Local recurrence, metastasis, and death were observed in 15 (14.0%), 19 (17.7%), and 13 (12.1%) of the participants, respectively. The 5-year local recurrence free survival (LRFS), metastasis-free survival (MFS) and disease specific survival (DSS) were 84.7%, 78.6%, and 87.8%, respectively (Fig. a-c). The independent risk factor for local recurrence was R1/2 margin at the dedifferentiated component of the tumor (Fig. d). Metastasis was associated with tumor size in the univariate analysis (Fig. e). The independent risk factor for DSS was tumor grade (Fig. f). Previous unplanned excision, de novo presentation, tumor depth, absence of the well-differentiated component, infiltrative border, R1/2 margin at the well-differentiated component were not associated with oncologic outcomes. Other primary malignancy and extrapulmonary metastasis were observed in 27 and 4 patients, respectively.

Conclusion: This is the largest study examining DDL-E to-date (Table). Localized DDL-E has low potential for metastasis and carries an excellent prognosis. Other primary malignancy and extrapulmonary metastasis are more frequent in DDL-E, thus close monitoring of other sites during follow-up is recommended. In surgical management of DDL-E, wide resection margins to secure R0 margin at the dedifferentiated component and marginal resection margin at the well-differentiated component are recommended.