Association of subcutaneous adiposity with survival outcomes in advanced biliary tract cancer treated with gemcitabine, cisplatin, and immune checkpoint inhibitor.

BACKGROUND: The obesity paradox, in which obese patients experience improved outcomes following immune checkpoint inhibitor (ICI) therapy, has been reported in several malignancies. However, its clinical relevance in advanced biliary tract cancer (BTC) remains unclear. METHODS: We retrospectively analyzed patients with advanced BTC who received first-line gemcitabine and cisplatin with ICI (ICI cohort; n = 68) or without ICI (non-ICI cohort; n = 179). Obesity was evaluated using body mass index (BMI) and computed tomography (CT)-based adipose tissue parameters, including total adipose tissue index (TATI), visceral adipose tissue index, and subcutaneous adipose tissue index (SATI). Skeletal muscle mass was quantified on CT images. Progression-free survival (PFS) and overall survival (OS) were assessed using Cox proportional hazards models. RESULTS: High TATI was associated with a lower prevalence of sarcopenia in both cohorts. In the ICI cohort, high SATI was independently associated with prolonged PFS (hazard ratio [HR], 0.45; P = 0.004) and OS (HR, 0.27; P = 0.001), whereas BMI and sarcopenia were not. High SATI showed a trend toward improved survival in both sarcopenic (P = 0.16) and non-sarcopenic subgroups (P < 0.001). In contrast, no significant associations between adipose tissue parameters and survival outcomes were observed in the non-ICI cohort. CONCLUSIONS: Higher subcutaneous adiposity was independently associated with improved survival outcomes in patients with advanced BTC receiving ICI therapy, but not in those treated without ICI, suggesting that it may serve as a clinically relevant prognostic factor in this setting.