All IHC used 4- to 5-μm-thick sections of formalin-fixed paraffin-embedded clinical tissues. ATM IHC was performed as described in Villaruz and colleagues (14 (link)). pRAD50 IHC was performed as described in Jones and colleagues (9 (link)). SLFN11 IHC was performed using a Leica Bond RX staining platform, the steps of which included dewaxing, pH9 antigen retrieval (ER2) for 25 minutes, protein blocking with SignalStain (Cell Signaling Technology), staining with 2.5 μg/mL anti-SLFN11 ab121731 antibody (Abcam), detection using the Polymer Refine Detection Kit (Leica), and counterstaining with hematoxylin (Leica). Appropriate control tissues and matched isotype controls were used during each staining run. Slides were digitalized using an Aperio AT2 scanner and pathology H-scores generated. H-scores are a product of the intensity of expression (0–3+) and percentage of cells stained. For ATM and SLFN11, which are both expressed in the nucleus, internal tissue control staining (e.g., lymphocytes) must be of 2+ or higher intensity for the sample to be deemed evaluable. A single pathologist performed the scoring at 20× magnification and the entire sample was assessed.