We envisioned a scenario where the interaction between the ATM-Chk2/ATR-Chk1 pathways and Hippo enables GC cells to overcome chemotherapy-induced death stimuli. First, ATM-Chk2 and ATR-Chk1 were found to be activated across all the GC molecular subtypes. Moreover, a number of genes associated with their basal activation are recurrently mutated or amplified.

Thus, we retrospectively characterized a cohort of GC patients treated with first-line therapy for DDR- and Hippo-related markers, identifying a signature predicting inferior PFS and OS. This exploratory analysis provided the necessary information (frequency of candidate biomarkers and effect difference between groups) for a prospective study with validation purposes, which is the main goal of this trial.

This prospective, multicenter, non-interventional trial is designed for prospectively validating the DDR-Hippo signature as a predictor of inferior PFS in patients with inoperable locally advanced or metastatic GC receiving first-line therapy. Patients will be evaluated for response to chemotherapy every two cycles by current RECIST criteria. PFS will be defined as the time elapsing between the initiation of chemotherapy until objective tumor progression or death, and OS as the time elapsing between the initiation of chemotherapy until death from any cause. All molecular analyses will be centralized at the coordinating center. Investigators performing molecular analyses will be masked to clinical outcomes. Centralized radiological review is planned. The study will be conducted in accordance with the Declaration of Helsinki and adheres to the REMARK criteria.

The second task is designed for exploring genetic events functionally related to the DDR and Hippo pathways that may modify the predictive significance of the signature. These genes are schematically clustered on the basis of the expected alteration in: i) Mutated genes (cluster 1) to be evaluated by targeted DNA-Seq and amplified genes (cluster 2) to be evaluated by FISH/CISH. Cluster 1 includes TP53 (defective cell cycle progression and apoptotic response, aberrant TAZ/YAP-mediated transcription), KRAS (oncogene-induced replication stress and activation of cell cycle checkpoints to avoid apoptosis and senescence), BRCA1 and BRCA2 (defective homologous recombination repair), ARID1A, ATR and ATM (altered ATM/ATR-initiated DNA repair), RHOA (G-protein coupled receptor-mediated activation of TAZ/YAP), CTNNB1, APC and FBXW7 (Wnt-mediated control of TAZ/YAP). Cluster 2 encompasses MYC and KRAS (oncogene-induced replication stress), CCNE1, CCND1 and CDK6 (dysfunctional G1-S transition requiring compensatory activation of intra-S and G2/M checkpoints).

The present study is designed to generate prospective evidence on the ability of the investigated biomarkers to predict the efficacy of first-line chemotherapy in GC patients. The identification of patients who derive marginal benefit from chemotherapy holds the potential to expedite a wave of interventional trials with agents targeting the DDR-Hippo network (e.g. PARP inhibitors and ATR-Chk1 and ATM-Chk2 inhibitors), as well as to delineate the target population for studies with other compounds, such as immune checkpoint inhibitors. Overall, the experimental approach we propose is expected to culminate in the generation of a new tool to be used on a routine basis.

Inclusion Criteria:

• Age >18 years;
• Histologic diagnosis of locally advanced or metastatic gastric carcinoma (GC) or gastroesophageal junction carcinoma (EJC);
• Biological material adequate for molecular analysis to be performed, taken (at surgery or by biopsy) prior to the administration of any anti-tumor treatment (chemotherapy and/or radiotherapy);
• ECOG PS 0-2;
• Adequate hematologic, hepatic, and renal function;
• Measurable disease according to RECIST criteria;
• Written informed consent.

Exclusion Criteria:

• Previous chemotherapy for metastatic disease;
• Comorbidities not controlled with appropriate medical therapy;
• Brain metastasis;
• Patient unable to give adequate consent for the study

Patients with inoperable locally advanced or metastatic GC who are candidates for first-line chemotherapy treatment and meet the following criteria will be included in the study