Would you treat a patient with refractory, metastatic castrate resistant prostate cancer who has somatic ATM mutation with a PARP inhibitor?

Yes, I would consider Olaparib (not Rucaparib), but only after they have received at least two AR-targeting drugs and at least one taxane drug, and only if an ATR inhibitor trial was not available. And I would set the expectations really low: PSA response rate of 5-10%, PFS of 4-6 months.