In retrospective studies performed on tissue samples from patient cohorts, RAD51 was shown to be a positive predictive biomarker of treatment response across multiple cancers, such as platinum-based chemotherapy in breast cancer and esophageal squamous cell carcinoma, as well as PARPi in pancreatic and prostate cancers [48,49,50]. This evidence concerns the gene RAD51 and esophageal squamous cell carcinoma.