Oral, Fecal and Intratumoral Microbiome Atlas in Colombian Patients With Advanced Solid Tumors Receiving First-Line Immunotherapy

Inclusion Criteria: * Age 18 years or older. * Histologically confirmed advanced (stage III unresectable or IV) gastric, colorectal, breast, cervical or head-and-neck cancer. * Candidate for first-line immunotherapy per current clinical guidelines. * Available FFPE tumor block in institutional or reference pathology archive. * Able to provide saliva and stool samples at V0 and follow-up. * ECOG performance status within protocol limits; life expectancy over 3 months. * Cognitive capacity to give informed consent; signed EVA-BIOBANCO and Atlas consents. Inclusion Criteria (healthy controls) * No prior cancer diagnosis. * No active autoimmune disease; no inflammatory bowel disease. * No antibiotics, invasive dental treatment, immunosuppressants or corticosteroids in the prior 3 months; no severe active periodontal disease. Exclusion Criteria: * Systemic antibiotics within 3 months (except short course under 5 days for uncomplicated infection). * Probiotics or prebiotics within 30 days. * Chronic proton-pump inhibitors for more than 3 continuous months. * Inflammatory bowel disease (Crohn, ulcerative colitis) or extensive bowel resection. * Pregnancy or lactation. * BMI under 18.5 or over 40 kg/m². * Uncontrolled diabetes (HbA1c at or above 9% in prior 3 months). * Invasive dental treatment within 3 months. * Patients: simultaneous randomized trial of a non-INVIMA-approved experimental immunotherapy; or no evaluable FFPE block meeting quality thresholds. * Inability to ensure 12-month clinical follow-up.