The phase II KEYLYNK-009 (NCT04191135) study evaluated maintenance pembrolizumab (pembro) + olaparib (ola) vs pembro + chemotherapy (chemo) in patients (pts) with metastatic TNBC who had clinical benefit from induction with first-line pembro + chemo. We present patient-reported outcomes (PROs) from this study to provide important evidence on the benefit/risk profile of these treatments. Eligible pts received induction therapy with pembro 200 mg Q3W + chemo (carboplatin AUC 2 + gemcitabine 1000 mg/m2 on days 1 and 8 per 21-day cycle) for 4–6 cycles. Pts with CR, PR, or SD were randomized 1:1 to pembro 200 mg Q3W + ola 300 mg BID or pembro + chemo (induction regimen) for up to 35 cycles (including induction). PROs were secondary endpoints and included changes from randomization (baseline) to week 18 (last time with completion/compliance ∼≥60%/80% in QLQ-C30) for EORTC QLQ-C30 GHS/QoL, QLQ-C30 physical and emotional functioning, QLQ-BR23 systemic therapy side effects, and EQ-5D-5L visual analogue scale (VAS). TTD (time from baseline to first onset of a confirmed ≥10-point deterioration) was also assessed. PROs were analyzed in randomized and treated pts who completed ≥1 PRO assessment. No alpha was assigned to PRO analyses. PRO analyses included 267 pts (pembro + ola, n = 135; pembro + chemo, n = 132). Completion/compliance in QLQ-C30 at week 18 was 59.3%/88.9% with pembro + ola and 62.1%/85.4% with pembro + chemo. No between-group differences were observed, except that TTD for QLQ-C30 GHS/QoL favored pembro + chemo (Table).Table: 198PBetween-group difference in change from baseline to wk 18 least-squares mean (95% CI)a (Pembro + Ola vs Pembro + Chemo)QLQ-C30 GHS/QoL−3.28 (−7.69 to 1.12)QLQ-C30 physical functioning−0.16 (−4.89 to 4.56)QLQ-C30 emotional functioning2.08 (−3.16 to 7.31)QLQ-BR23 systemic therapy side effects0.93 (−2.20 to 4.06)EQ-5D-5L VAS−0.37 (−4.03 to 3.28)TTD HR (95% CI)b (Pembro + Ola vs Pembro + Chemo)QLQ-C30 GHS/QoL1.78 (1.16–2.71)QLQ-C30 physical functioning1.01 (0.61–1.69)QLQ-C30 emotional functioning1.08 (0.69–1.71)QLQ-BR23 systemic therapy side effects1.76 (0.88–3.53)aBased on a constrained longitudinal data analysis model (cLDA).bBased on stratified Cox regression model. Open table in a new tab aBased on a constrained longitudinal data analysis model (cLDA). bBased on stratified Cox regression model. In pts with metastatic TNBC, stopping chemo in pts with responding or stable disease and treating with maintenance pembro + ola showed similar PRO results when compared with pts who continue pembro + chemo.