(P 134) REAL-WORLD CLINICAL OUTCOME OF NEOADJUVANT CHEMOTHERAPY FOR RETROPERITONEAL DEDIFFERENTIATED LIPOSARCOMA

Objective: Complete tumor resection is the only promising strategy associated with survival benefits for retroperitoneal sarcoma (RPS). On the other hand, the role of systemic chemotherapy (CT) for RPS remains controversial.
For dedifferentiated liposarcomas (DDLPS) in particular, the overall response rate (ORR) for anthracycline-based regimens as primary systemic treatment has been reported to be 10-20%, but previous studies include cases with primary sites elsewhere, such as the extremities, or a mix of both perioperative and unresectable/metastatic cases, there are very few data specific to the neoadjuvant treatment.
The aim of this study is to clarify the efficacy and safety of neoadjuvant chemotherapy (NAC) for DDLPS in real-world clinical practice.

Methods: We retrospectively examined 29 patients with primary retroperitoneal DDLPS who received NAC with an anthracycline-based regimen and underwent initial surgery at the National Cancer Center Hospital in Japan between April 2011 and March 2022.
The efficacy of chemotherapy was assessed according to RECICT 1.1 and safety according to CTCAEv5.0. Clinical characteristics and survival were compared with those of DDLPS who underwent surgery only without NAC (n=85) using the χ2 and Mann-Whitney tests. Survival analyses with overall survival (OS) and disease-free survival (DFS) were performed using the Kaplan-Meier method.

Results: Median age at the start of NAC was 54.7 years old (range: 38-75) and 62.1% (n=18) of patients were male. 86.2% (n=25) of patients were also had some symptoms, the most common was abdominal pain (44.8%).
The purpose of NAC was expected to achieve complete resection by tumor shrinkage in 62.1% (n=18), disease control due to rapid growth in 20.7% (n=6), symptom control in 10.3% (n=3) and time control in 6.9% (n=2). Surgery was performed in all cases after NAC.
Treatment regimens were doxorubicin plus ifosphamide (AI) in 69.0% (n=20) and doxorubicin alone in 31.0% (n=9) respectively. Two patients demonstrated partial response, while two exhibited progressive disease, resulting in the ORR of 6.9% and the disease control rate (DCR) of 93.1%.
Median OS was 49.7 months (95% CI: 40.9-58.4) and median DFS was 15.8 months (95% CI: 3.6-27.9), neither of which was superior to the surgery-only group. OS in surgery-only group has not reached median and median DFS was 26.3 months (95% CI: 16.7-35.8).
The NAC group was significantly younger than the surgery-only group (54.7 vs. 62.2 years, p=0.003), and there were no significant differences between the two groups in terms of operative time, blood loss or incidence of perioperative complications. There was a trend towards fewer segmental resections (p=0.042) and R2 resection margins (p=0.052) in NAC group.
Regarding safety, Grade 3 or higher adverse events were observed in 69.0% (n=20), with hematological toxicities in 58.6% (n=17) of patients, but no chemotherapy-related deaths.

Conclusion: This study showed the real-world date of NAC for retroperitoneal DDLPS. The survival benefit of NAC was not observed in the present study. Nevertheless, in this study the NAC group included the patients who demonstrated rapid growth of tumor or required R2-resection.
The safety of NAC is tolerable, there is no apparent negative effect on surgery, and there seems to be some potential of improving prognosis, such as securing resectable margins due to tumor shrinkage.
A prospective trial of NAC for resectable DDLPS as STRASS2 is currently ongoing and needs to be validated and compared with its results.