Metformin Plus Irinotecan for Refractory Colorectal Cancer

Inclusion Criteria: * 18 years or older * Biopsy-proven colorectal adenocarcinoma * Ineligibility for curative intent therapy, e.g., surgery or radiation * Disease progression after oxaliplatin (either adjuvant or palliative), fluoropyrimidine (either adjuvant or palliative), irinotecan, and if Kras wild type a anti-EGFR therapy * Assessable disease according to RECIST v1.1 Exclusion Criteria: * known hypersensitivity to metformin or irinotecan * Uncontrolled Central nervous system metastasis * Acute or chronic severe infection