The challenges with the RAD51 foci assay include exam timing (pre- or posttreatment), tissue resources (primary tumor, ascites, or FFPE), methods of inducing DNA damage (radiation, platinum, or PARPi), methods of detection (immunofluorescence or immunohistochemistry), measurement of RAD51 foci (numbers or percentages), intratumor or interobserver variability, and the definition of HRD in correlation with the clinical response (125, 126, 149). This evidence concerns the gene RAD51 and neoplasm.