EP 494 Can CT-Derived Skeletal Muscle Metrics Guide Treatment Decisions in Lavage Cytology–Positive Patients with Gastric Cancer Undergoing Conversion Therapy?

Abstract Aims To determine the impact of pre-treatment sarcopenia, newly developed sarcopenia after therapy, and significant muscle loss (SML) during conversion therapy on conversion success, tumour response, and survival in patients with GC-CY1. Methods Retrospective analysis of GC-CY1 patients from a prospective conversion therapy trial between Apr 2018 and Aug 2019. CT-derived skeletal muscle index (SMI) was measured at L3. Sarcopenia was defined using published cut-offs. Multivariable logistic regression assessed conversion success; Cox regression assessed overall survival (OS) and progression-free survival (PFS). Results 36 patients were included. Sarcopenia prevalence was 19.4% pre-treatment; 16.7% developed new sarcopenia post-treatment; and 22.2% developed SML during therapy. On multivariable analysis, both pre-treatment sarcopenia and SML during therapy were associated with reduced conversion therapy success. Pre-treatment sarcopenia independently predicted worse OS (HR 6.341, 95%CI 1.269–18.943, p=0.001) and PFS (HR 8.212, 95%CI 1.569–36.582, p=0.001). Newly developed sarcopenia after conversion therapy predicted worse OS (HR 3.189, 95%CI 1.023–9.811, p=0.012) and PFS (HR 3.084, 95%CI 1.042–14.236, p=0.013). Presence of SML during therapy had the strongest association with poor outcomes (OS HR 10.234, 95%CI 2.532–54.231, p=0.002; PFS HR 9.562, 95%CI 2.341–38.092, p=0.002). Conclusion Pre-treatment sarcopenia and interval skeletal muscle loss during conversion therapy are strongly associated with reduced conversion success and markedly worse OS/PFS. CT may provide a pragmatic imaging biomarker to guide risk stratification during treatment.