Neoadjuvant atezolizumab plus docetaxel/oxaliplatin/capecitabine in non-metastatic gastric and gastroesophageal junction adenocarcinoma: The PANDA trial

4059 Background: Immune checkpoint blockade improves clinical outcomes for patients with gastric and gastro-esophageal junction (GEJ) cancers, but its efficacy and impact on the tumor microenvironment in non-metastatic, resectable disease remains largely unknown. Peri-operative FLOT, the current standard-of-care, leads to pathologic complete responses (pCR) and major pathologic responses (MPR) in 16% and 37% of patients, respectively. An important open question is whether PDL-1 blockade monotherapy can prime the tumor microenvironment in a favorable manner, prior to combination with chemotherapy. Methods: We report results from the phase 2 PANDA trial (NCT03448835) of neoadjuvant atezolizumab (anti-PDL-1) plus docetaxel, oxaliplatin, and capecitabine (DOC) in patients with resectable gastric or GEJ adenocarcinoma. Patients received a single cycle of atezolizumab monotherapy, followed by 4 cycles of atezolizumab+DOC. Tumor tissue was collected at baseline, after atezolizumab monotherapy, the first atezolizumab+DOC, and at resection. The primary endpoints were safety and feasibility in 20 patients, and secondary endpoints included MPR (