We have reported here the cases of 2 patients with multi-treated metastatic CRC...The patient received 3 mo of olaparib therapy without toxicity. Despite the absence of toxicity, the magnetic resonance imaging (Figure ​(Figure2)2) showed tumor progression. Olaparib was stopped and the patient was included in a phase I clinical trial....Additional genetic analyses revealed a frameshift truncating mutation of the TP53BP1 gene in the patient who progressed.