IntOGen List Cohorts

List available cancer cohorts from IntOGen with sample counts and tumor types. Returns cohort IDs, names, data sources (TCGA, ICGC, Hartwig, etc.), sample counts, tumor type (Primary/Metastasis), and age group (Adult/Pediatric). Optionally filter by cancer type. IntOGen includes 271 cohorts from major genomic studies. Example: cancer_type='BRCA' returns 14 breast cancer cohorts from TCGA, Hartwig, ICGC, and others.