203P Clinical effectiveness of olaparib in BRCA-mutated, HER2-negative metastatic breast cancer (mBC) by ER expression level: Subgroup analysis from phase IIIb LUCY trial

In the OlympiAD phase III trial, olaparib significantly prolonged progression-free survival (PFS) vs chemotherapy in patients (pts) with germline-BRCA-mutated (gBRCAm), HER2-negative mBC regardless of hormone receptor (HR) status. a study population that reflects clinical practice, IIIb LUCY trial similarly showed effectiveness HR ASCO/CAP guidelines highlight lack data on best treatment approach for breast tumors are estrogen (ER)-low (1–10% ER+ stained cells). We examined by ER expression pts gBRCAm from trial. this open-label germline or somatic BRCAm, received (300 mg BID). Pts had ≤2 lines and taxane and/or anthracycline (neo)adjuvant setting. BC endocrine therapy. post hoc subgroup analysis (data cut-off Sept 1, 2021), were grouped (ER <1%; 1–10%; >10% IHC) analysed PFS, overall survival, response rate (CRR; i.e. proportion assessed as responding investigator [radiological symptomatic] at ≥1 visit), duration response. 251/252 cohort included <1% n=117; 1–10% n=29; n=105). At baseline, group shorter median times their original diagnosis (29.7 52.0 58.6 mo) (4.8 11.1 12.5 groups, respectively. Efficacy outcomes consistent across subgroups (Table).Table: 203PEfficacy results expressionER <1%ER 1–10%ER >10%Median months (95% CI)92/117*6.8 (5.5–9.0)24/29*8.3 (4.5–12.6)89/105*8.4 (7.6–11.0)Median OS, CI)67/117*20.1 (16.5–26.9)20/29*22.9 (13.0–35.1)54/105*27.4 (23.0–NR)CRR, % CI)59/116*50.9 (41.4–60.3)12/28*42.9 (24.5–62.8)51/104*49.0 (39.1–59.0)Median DOCR, (IQR)59/116*8.3 (3.8–26.5)12/28*7.2 (5.3–14.1)51/104*7.4 (4.3–17.7)∗number events responses/number evaluable pts.CI, confidence interval; CRR, rate; response; IQR, interquartile range; NR, not reached; survival; survival. Open table new tab ∗number pts. CI, Real-world support gBRCAm, mBC, level.