The aim of this study was to identify synthetically lethal interactions between ATR and certain DNA-repair genes, applying a siRNA library of all major DNA-repair genes in a well-characterized genetic ATR knock-in model of DLD1 colorectal cancer (CRC) cells [14, 22, 23] harboring the hypomorphic ATR-Seckel mutation. The gene discussed is ATR; the disease is colorectal carcinoma.