(P 135) SURVIVAL OUTCOMES AND TREATMENT PATTERNS FOR PATIENTS WITH DEDIFFERENTIATED LIPOSARCOMA: A RETROSPECTIVE COHORT STUDY IN ONTARIO, CANADA

Objective: Dedifferentiated liposarcoma (DDLPS) is a rare and high-grade tumor. In the advanced/metastatic setting, this disease is associated with low survival rates. Treatment patterns and survival outcomes for DDLPS patients have not been previously studied in Canada. This real-world evidence (RWE) study aims to assess the prevalence, treatment patterns and clinical outcome of patients with DDLPS in Ontario, Canada.

Methods: A retrospective cohort study was conducted in Ontario, Canada, using the Institute of Clinical Evaluative Sciences (ICES) databases. Patients with a new diagnosis of DDLPS (ICD-0-3 code: 8858/3) were identified in the Ontario Cancer Registry between January 2010 and December 2022 and followed until December 2023, a gap in health coverage or death, whichever occurred first. Study outcomes included cumulative prevalence, treatment patterns, mortality rates and median overall survival (mOS) for DDLPS patients. Predictors of mortality for DDLPS were assessed using a Cox regression model adjusted for key baseline characteristics. mOS was also examined in patients with (1) advanced, metastatic, or recurrent disease (defined as stage III and IV DDLPS at time of diagnosis or patients who received chemotherapy during the follow-up), and (2) unresectable tumor (defined as not having surgery within 6 months of DDLPS diagnosis).

Results: From 2010 to 2022, the prevalence of DDLPS in Ontario was 1.995 per 100,000 people and the mortality rate was 0.226 per 100,000. After excluding patients with previous cancers within 5 years of their DDLPS diagnosis, 611 incident cases were identified (65% male, median age (IQR): 67 [57-76] years). The most common DDLPS topography site was the retroperitoneum (60.6%). The mOS [IQR] was 69 months [15-151]; Stage I-IV cancer were associated with a mOS of 85 [43-NA], 103 [30-NA], 79 [19-145] and 8 [6-NA] months, respectively (Table 1). Patients with advanced, metastatic or recurrence DDLPS (40.3%) had a lower mOS compared to non-advanced disease (53 [15-108] vs 103 [16-NA] months, p< 0.0001). Similarly, unresectable DDLPS was associated lower mOS compared to resectable disease (38 [9-115] vs 131 [57-NA] months, p< 0.0001). After adjusting for baseline characteristics (HR, [95% CI]), patients aged ≥65 years (2.10, [1.66-2.67]), with retroperitoneum DDLPS (1.33, [1.06-1.66]) and stage IV cancer (6.80, [3.79-12.21]) were at higher risk of mortality compared to younger patients, those with other typologies and Stage I cancer.

Amongst 117 patients (19%) who received first-line (1L) treatments, doxorubicin regimen (DOXO) was the most prescribed drug (81.2%), followed by gemcitabine regimen (GEMC) (13.7%) and other therapies (OTHER) (5.1%). Median time (IQR) from diagnosis to 1L treatment was 6.5 (2.3-20.3) months, 24.9 (2.8-34.5) months, and 18.7 (1.8-61.5) months for DOXO, GEMC and OTHER, respectively. Median (IQR) duration on 1L treatment was 1.7 (0.7-3.7) months, 1.5 (1-5) months, and 1.2 (0.5-4.5) days for DOXO, GEMC and OTHER, respectively. mOS (IQR) for 1L treatment was 16 (6-58) months. Amongst 41 patients who received second-line (2L) treatments (35%), median duration (IQR) on treatment was 1.5 (0.7-3) months and mOS (IQR) was 9 (5-16) months. Among patients who received DOXO as 1L treatments, 32.6% received 2L treatment: 54.8% received GEM and 45.2% received OTHER.

Conclusion: This is the first comprehensive RWE study on DDLPS in Canada. Findings from this study suggest that DOXO and GEMC continue to be the standard of care for DDLPS in Ontario. However, patients with advanced disease experience delays in receiving treatments and have low survival rates. Newer and more effective treatments are needed to improve survival and potentially lower the financial impact on Canada’s already strained healthcare system.