RAD51 and neoplasm: Because of the difficulty of examining RAD51 foci numbers in tumor xenograft tissue samples, we examined the molecular mechanisms underlying niraparib synthetic lethality in hATM (−/−) tumor xenografts by examining RAD51 and γH2AX protein expression levels following a prolonged niraparib treatment period (50 mg/kg QD dosing regimen for a period of ~45 days).