Early Tumor Shrinkage and Depth of Response as Predictors of Survival for Advanced Biliary Tract Cancer: An Exploratory Analysis of JCOG1113

Background Recent studies suggest that early tumor shrinkage (ETS) and depth of response (DpR) reflect outcomes of chemotherapy in various cancers. This study evaluated the association of ETS and DpR with clinical outcomes using data from JCOG1113, which demonstrated the non-inferiority of gemcitabine plus S-1 (GS) to gemcitabine plus cisplatin (GC) for chemotherapy-naive advanced biliary tract cancer. Material and Methods In total, 354 (289 with measurable target lesions) patients enrolled in JCOG1113 were divided into ETS-unachieved and ETS-achieved groups (& GE;20% tumor reduction at week 6) and DpR-low and DpR-high groups (& GE;40% maximum shrinkage) until 12 weeks after enrollment. The impact of ETS and DpR on survival outcome was evaluated using the multivariable Cox proportional hazard model. Results The proportions of patients in the ETS-achieved and DpR-high groups were similar between the 2 treatment arms. The hazard ratios (HRs) of progression-free survival (PFS) and overall survival (OS) for the ETS-achieved group were 0.70 (95% confidence interval (CI), 0.52-0.93) and 0.60 (95%CI, 0.44-0.81), respectively. The HRs of PFS and OS for the DpR-high group were 0.67 (95%CI, 0.48-0.94) and 0.64 (95%CI, 0.46-0.90), respectively. In the subpopulation treatment effect pattern plot analysis, most patients in the ETS-achieved group in the GC arm did not experience disease progression after 12 weeks from the landmark. Conclusion As on-treatment markers, ETS and DpR were effective tools. ETS was clinically useful, because it can be used to evaluate the outcomes of treatment early at a specific time. This article evaluates the association between early tumor shrinkage and depth of response with clinical outcomes in patients with advanced biliary tract cancer using data from JCOG1113.