Multi-omics Sequencing in Neoadjuvant Immunotherapy of Gastrointestinal Tumors

This study collects tumor tissue and blood samples from patients with locally advanced or metastatic stomach, gastroesophageal junction, or rectal cancers to perform detailed genetic and molecular analysis (multi-omics sequencing). The goal is to understand why some patients respond to immunotherapy (neoadjuvant treatment) and others do not, helping to develop better, personalized therapies. **You may be eligible if...** - You are 18 or older - You have locally advanced or metastatic stomach, gastroesophageal junction, or rectal adenocarcinoma - Your tumor has been tested and confirmed to be of a specific molecular subtype (pMMR/MSS) - You are willing to provide fresh tumor tissue and blood samples for analysis - You are scheduled to receive neoadjuvant (pre-surgical) treatment as part of your care **You may NOT be eligible if...** - You have already received systemic treatment for this cancer - Your tumor does not have the required molecular characteristics - You are unable or unwilling to provide tissue samples - You have other serious illnesses that would prevent participation Talk to your doctor to see if this trial is right for you.