PD-L1 expression and survival in unresectable/recurrent gastric cancer treated by 1st-line treatment without immune checkpoint inhibitors: JCOG1013A1.

BACKGROUND: The prognostic significance of PD-L1 expression in unresectable/recurrent gastric cancer treated by first-line chemotherapy without an immune checkpoint inhibitor (ICI) remains unclear. The phase III trial JCOG1013 demonstrated no overall survival (OS) or progression-free survival (PFS) benefit of docetaxel/cisplatin/S-1 over cisplatin/S-1. This ancillary analysis of JCOG 1013 evaluated the prognostic value of PD-L1 expression. METHODS: PD-L1 expression was assessed in pretreatment tumor specimens using the Dako 28-8 pharmDx assay. Combined positive score (CPS) and tumor proportion score (TPS) were calculated. PD-L1 positivity was defined as CPS ≥ 5 or TPS ≥ 1%. Univariable and multivariable analyses were performed for OS and PFS. RESULTS: Among 741 patients enrolled in JCOG1013, 540 patients were included. In univariable analyses, neither CPS ≥ 5 nor TPS ≥ 1% was significantly associated with OS or PFS. In multivariable analyses, CPS ≥ 5 was not significantly associated with OS (HR 0.86, 95% CI 0.71-1.04; p = 0.127) or PFS (HR 0.92, 95% CI 0.77-1.11; p = 0.392); however, TPS ≥ 1% was significantly associated with longer OS (HR 0.78, 95% CI 0.62-0.97; p = 0.028) and PFS (HR 0.76, 95% CI 0.62-0.94; p = 0.012). CONCLUSIONS: TPS ≥ 1% is an independent favorable prognostic factor for survival in patients with unresectable/recurrent gastric cancer receiving chemotherapy alone. CLINICAL TRIAL REGISTRATION: UMIN000007652.