Characterizing the transformation and diagnosis of atypical lipomatous tumors to dedifferentiated liposarcoma: Single-institutional outcomes.

Abstract

e23560 Background: Atypical lipomatous tumor (ALT) is a locally aggressive, benign adipocytic tissue mass with risk of transformation into dedifferentiated liposarcoma (DDLS), a mixed-grade, non-lipogenic tumor with increased risk for metastasis and mortality. Studies have evaluated the dedifferentiation rate of DDLS but seldom report the methodology of obtaining their diagnosis, which is crucial due to their heterogeneous architecture and relatively low core needle biopsy (CNB) accuracy. We included a longitudinal cohort of ALT/DDLS patients characterizing how and when patients received their diagnoses. Methods: 168 patients diagnosed with ALT-only (n = 129), DDLS-only (n = 22), or both (n = 17) were included. Among DDLS patients, the presence of a prior ALT diagnosis along with time between their ALT and DDLS diagnosis was measured. Histology, location, results, and methods of each diagnosis were recorded including, CNB, surgical resection, or both. Disease-specific survival (DSS) and recurrence free-survival (RFS) were calculated with univariate/multivariate analysis for risk factors. Results: Among patients who received a diagnosis with CNB consistent with ALT, 7 were subsequently diagnosed with DDLS after surgical resection, representing 4.8% of ALT patients. Mean time between diagnoses was 2.3 months (STD 2.0). 5 (3.4%) patients were diagnosed with a DDLS recurrence after initial ALT diagnosis confirmed with CNB and surgical resection. Median time between diagnoses was 37.0 months (IQR 16.0, 63.0). 5 (3.4%) had tumors with a heterogeneous composition on initial surgical resection, described as an ALT with dedifferentiated components. 22 DDLS patients had no prior ALT diagnosis. 9 were diagnosed from both CNB and surgical resection, and 13 were diagnosed from surgical resection directly after clinical suspicion and imaging concerning for sarcoma. DSS in the DDLS was significantly lower than ALT-only DSS (p < 0.0001). There was no significant difference in RFS. Conclusions: DDLS may arise after an extended period of time after ALT resection or simultaneously with an ALT diagnosis. Due to its varied diagnostic timeline and appearance, caution is advised when evaluating and treating ALT. [Table: see text]