Dkn-01 In Combination With Pembrolizumab In Patients With Advanced Gastroesophageal Adenocarcinoma (Gea): Tumoral Dkk1 Expression As A Predictor Of Response And Survival

357 Background: Dickkopf-1 (DKK1) modulates Wnt signaling and contributes to an immune suppressive tumor microenvironment. DKN-01 (D), a neutralizing DKK1 antibody + pembrolizumab (P) has demonstrated safety and clinical activity in advanced GEA. We report response and survival outcomes in anti-PD-1/anti-PD-L1 naïve GEA patients by high/low tumoral DKK1 expression. Methods: We enrolled advanced anti-PD-1/PD-L1 naïve GEA patients (pts) in a Phase 1b/2a study of D + P (NCT02013154). Tumoral DKK1 mRNA expression was assessed by an in situ hybridization RNAscope assay. Objective response rate (ORR), disease control rate (DCR), progression free survival (PFS) and overall survival (OS) were compared between DKK1 high and low groups. Kaplan-Meier method and Cox-PH model was used for survival analysis and logistic regression was used for clinical benefit/response outcome. Results: 34 GEA pts were enrolled to receive 300 mg D + P. 31 GEA pts had DKK1 expression available (25 response-evaluable/RE) and 27 had both DKK1 and PD-L1 expression available (22 RE). In RE pts, DKK1 high (H-score ≥ upper-tertile [≥35]) had an ORR of 50% (5 PR/10), DCR of 80% (8/10) while DKK1 low ( < upper-tertile) had an ORR of 0% (0/15) and DCR of 20% (3/15); DKK1 high (vs. low) had an OR of 16 (95%CI: 2.2, 118.3; n = 25) and adjusted (for PD-L1 CPS ≥10 vs. < 10) OR of 17.6 (95%CI:1.6, 194.4; n = 22) for clinical benefit/response (PR/SD vs. PD). Median PFS was 22.1 weeks in DKK1 high (n = 11) vs. 5.9 weeks in DKK1 low (n = 20); HR of 0.23 (95%CI: 0.082, 0.66; n = 31). Adjusted (for PD-L1 expression) HR for DKK1 high was 0.20 (95%CI: 0.061,0.68; n = 27) for PFS. DKK1 high (n = 11) had a median OS of 31.6 weeks vs. 17.4 weeks in DKK1 low (n = 20); HR of 0.45 (95%CI: 0.16, 1.3; n = 31) and adjusted HR of 0.62 (95%CI: 0.2,1.9; n = 27). Conclusions: High levels of tumoral DKK1 expression identify advanced anti-PD-1/PD-L1 naïve GEA pts with the greatest benefit from D + P. Improvements in response/clinical benefit and PFS were observed independent of PD-L1 expression. Tumoral DKK1 as a potential predictive biomarker for DKN-01 treated GEA pts will be evaluated in future studies. Overall survival follow-up is ongoing. Clinical trial information: NCT02013154.