(P 331) MAINTENANCE THERAPY (M-TP) WITH DACARBAZINE (DTIC) AFTER FIRST-LINE ANTHRACYCLINE-BASED DOUBLET IN ADVANCED LEIOMYOSARCOMA (LMS) PATIENTS (PTS): OUTCOMES OF A CASE SERIES IN A SINGLE REFERRAL CENTER

Objective: Doublet chemotherapy (ChT) with adriamycin and dacarbazine (ADM-DTIC) represents a first-line (1L) option for advanced LMS pts. Due to cumulative anthracycline toxicity, ChT is usually limited to six cycles (6c). The potential benefit of single-agent DTIC m-tp in pts achieving disease control after ADM-DTIC remains unclear. This study aims to explore the efficacy of adopting DTIC m-tp after ADM-DTCI on survival outcomes.

Methods: All consecutive metastatic LMS pts receiving ADM-DTIC as 1L tp from January 1st, 2015, at our institution, were retrieved. Pts with stable disease (SD) or partial response (PR) after ≥ 3 cycles (≥ 3c) were included in this analysis. On the evaluable pts, Overall Survival (OS) and Progression-Free Survival (PFS) were evaluated by using Kaplan Meier (KM) method. Time to event was calculated from the date of the ADM-DTIC treatment start. KM curves, stratified for the administration of DTIC m-tp were also constructed for both OS and PFS, and the median OS (mOS) and PFS (mPFS) were calculated. Cox model was used to estimate the effect of DTIC m-tp on OS and PFS and hazard ratios (HRs) were reported; pts on active surveillance (AS, i.e., not receiving DTIC m-tp), were considered the reference group.

Results: Of 52 metastatic LMS pts receiving ADM-DTIC as 1L tp, 28 were SD or PR after ≥3c and 24/28 were evaluable at the time of this analysis. Median age was 53 years, 18/24 were females, and the median follow-up was 38 months (mos); mOS and mPFS were 54 mos (IQR, 22 - 77) and 11 mos (10-21) respectively; mOS was 24 mos (19-77) for patients in DTIC m-tp and 54 mos (22-65) for pts in AS (HR: 1.26, p=0.734); mPFS was 11 mos (7-18) for patients in DTIC m-tp and 12 mos (10-28) for pts in AS (HR: 2.28, p=0.107).

Conclusion: In this retrospective single-center case series, DTIC m-tp following initial ADM-DTIC doublet did not show a survival benefit for advanced LMS pts both in terms of OS and PFS. However, results may reflect selection bias, as pts with higher tumor burden or symptomatic disease were likely favored for maintenance. Multicenter studies with standardized criteria are warranted to clarify DTIC maintenance benefits.