The SOLO1 trial evaluated the efficacy of maintenance olaparib in patients with newly diagnosed advanced ovarian cancer and a BRCA1/2 mutation. The study was an international, randomized, double-blind, phase 3 trial involving 391 patients who were randomly assigned in a 2:1 ratio to receive either olaparib (300 mg twice daily) or placebo. The primary endpoint was progression-free survival, defined as the time from randomization to disease progression or death. After a median follow-up of 41 months, the risk of disease progression or death was 70% lower with olaparib than with placebo (Kaplan–Meier estimate of freedom from disease progression and death at 3 years: 60% vs. 27%; hazard ratio, 0.30; 95% CI, 0.23 to 0.41; P<0.001). Adverse events were consistent with the known toxic effects of olaparib. The median progression-free survival was 13.8 months in the placebo group, which is consistent with results from studies of carboplatin plus paclitaxel in patients with newly diagnosed advanced ovarian cancer and a BRCA1/2 mutation. The safety profile of olaparib was generally acceptable, with a low incidence of serious adverse events. The results suggest that maintenance therapy with olaparib provides a substantial benefit in terms of progression-free survival for women with newly diagnosed advanced ovarian cancer and a BRCA1/2 mutation.The SOLO1 trial evaluated the efficacy of maintenance olaparib in patients with newly diagnosed advanced ovarian cancer and a BRCA1/2 mutation. The study was an international, randomized, double-blind, phase 3 trial involving 391 patients who were randomly assigned in a 2:1 ratio to receive either olaparib (300 mg twice daily) or placebo. The primary endpoint was progression-free survival, defined as the time from randomization to disease progression or death. After a median follow-up of 41 months, the risk of disease progression or death was 70% lower with olaparib than with placebo (Kaplan–Meier estimate of freedom from disease progression and death at 3 years: 60% vs. 27%; hazard ratio, 0.30; 95% CI, 0.23 to 0.41; P<0.001). Adverse events were consistent with the known toxic effects of olaparib. The median progression-free survival was 13.8 months in the placebo group, which is consistent with results from studies of carboplatin plus paclitaxel in patients with newly diagnosed advanced ovarian cancer and a BRCA1/2 mutation. The safety profile of olaparib was generally acceptable, with a low incidence of serious adverse events. The results suggest that maintenance therapy with olaparib provides a substantial benefit in terms of progression-free survival for women with newly diagnosed advanced ovarian cancer and a BRCA1/2 mutation.