RecruitingDrug trialOral, Fecal and Intratumoral Microbiome Atlas in Colombian Patients With Advanced Solid Tumors Receiving First-Line ImmunotherapyThis is a prospective observational cohort study conducted at Fundación CTIC in Bogotá, Colombia. It characterizes the oral, fecal and intratumoral microbiome of Colombian adults with advanced solid tumors (gastric, colorectal, breast, cervical and head-and-neck cancer) who receive first-line immunotherapy as standard of care, and compares them with healthy volunteers. Using multi-omics (HiFi metagenomics, 16S, tumor RNA-Seq and untargeted metabolomics), the study aims to identify microbial signatures associated with treatment response and survival, building the initial Colombian cohort of a Cancer Microbiome Atlas with Latin American projection.