A minimally invasive way to detect tumor genomic alterations is through analysis of circulating tumor DNA (ctDNA); we and others have previously reported BRCA2 and PALB2 reversion mutations in the ctDNA of patients with mCRPC at disease progression after response to PARPi.12–14 To further characterize the landscape of acquired PARPi resistance in mCRPC, we performed serial ctDNA longitudinal analyses in men whose tumors responded on the TOPARP-B trial and had HRR gene pathogenic mutations, or BRCA2 homozygous deletions. The gene discussed is PALB2; the disease is neoplasm.