Fig 1: The proposed preclinical and clinical flow to potentially predict ATRi-sensitive and ATRi-resistant colorectal cancer tumors. After written consent of the patient, tumor sample can be either processed as FFPE sample for direct immunohistologic and immunofluorescence analysis, or preclinical models for in vitro and in vivo analyses can be established. Samples can be tested for direct in vitro drug screenings or for biomarkers analysis through immunofluorescence or IHC assays. To evaluate the relevance of the “composite biomarker” of sensitivity to ATR inhibition, we propose to detect the expression level of proteins ATM, RAD51, and RAD51C together with scoring of phospho-RPA32 at basal level—prior to treatment. Also, scoring of activated DNA-PK and RAD51 upon treatment with ATRi will be informative. This information may eventually lead to the identification of patients who might benefit from ATR inhibition monotherapy, and directly translate the knowledge from bench to bedside. FFPE, formalin-fixed, paraffin-embedded; PDO, patient-derived organoid; PDX, patient-derived xenograft; TTT, treatment. This figure was created with biorender.com.