Biomarker allocation to the rucaparib comparison was based on =10% genomic loss of heterozygosity (%LOH) and/or somatic alteration in defined DRD associated genes (ATM, BARD1, BRCA1, BRCA2, BRIP1, CDK12, CHEK2, FANCA, NBN, PALB2, RAD51, RAD51B, RAD51C, RAD51D, RAD54L) and/or germline BRCA1 or BRCA2 alteration.74 of 279 (26.5%) screened patients were biomarker positive. 40 were randomised within the rucaparib comparison (Dec 2017-Dec 2020). Biomarker positive status was by high %LOH in 22 (55%), DRD gene alteration in 11 (27.5%) and both in 7 (17.5%). Patient characteristics (median age 70.5; 82.5% male; 87.5% bladder primary; 52.5% ECOG PS 0; 62.5% prior cisplatin; 45% visceral metastases) were balanced by treatment arm. 12 (60%) and 20 (100%) PFS events have occurred in the rucaparib and placebo arms respectively (median duration follow up 94.6 weeks in those still alive). Median PFS was 35.3 weeks (80% confidence interval (CI) 11.7-35.6) with rucaparib and 15.1 weeks (80% CI 11.9-22.6) with placebo (hazard ratio 0.53, 80% CI 0.30-0.92, 1 sided p = 0.07).Maintenance rucaparib, following PBC, extended PFS in DRD biomarker selected patients with mUC and is tolerable.