Background: Gastric carcinoma (GC) is the third-leading cause of death in China (291,000 deaths in 2015). Current therapies include surgery, chemotherapy, radiotherapy and targeted therapy, which prolong PFS and OS to 6 months and 8-14 months, respectively. Tumor Treating Fields (TTFields) are a non-invasive, regional antimitotic treatment modality approved by the FDA for glioblastoma and malignant pleural mesothelioma. TTFields at specific frequency (100- 500 kHz) are delivered via transducer arrays placed on the skin of the upper abdomen, back, right and left hypochondriac regions where the primary tumor lesion is located. TTFields were effective in preclinical models of gastric cancer and there are several ongoing Phase 3 trials of TTFields in multiple solid tumors. In this phase 2, single arm, open-label, multi-center study, we will investigate for the first time the efficacy and safety of TTFields concomitant with XELOX (oxaliplatin/capecitabine) as the first-line treatment of GC. Methods: Patients (N = 50) with histologically confirmed unresectable, locally advanced or metastatic Gastroesophageal Junction (GEJ) or Gastric Adenocarcinoma (GC), aged ≥ 18 years, ECOG PS 0-1, who had no previous systemic treatment for the recurrent or metastatic disease will be enrolled. Patients will receive TTFields (150 kHz via the NovoTTF-100L (P) medical device for average monthly use of 18 hrs/day) plus XELOX chemotherapy (Oxaliplatin: 130 mg/m2 on day 1 every 3 weeks; Capecitabine: 1000 mg/m², PO, BID on day 1-14 every 3 weeks). For HER-2 positive patients, trastuzumab is allowed. The primary endpoint is investigator-assessed Objective Response Rate (ORR) per RECIST 1.1. Secondary endpoints are time to tumor progression (TTP), progression-free survival (PFS), overall survival (OS), and 12-month OS rate. Adverse events (AEs) will be graded for severity according to CTCAE 5.0. Based on the historical ORR data in first-line chemotherapy in GC, we assumed that ORR will be higher than 45% with TTFields concomitant with chemotherapy. At least 45 patients need to be enrolled to ensure the lower boundary is 30% of the 95% CI. Estimating a patient drop-out rate of 10%, 50 patients will be actually enrolled.