Background: Although endocrine therapy (ET) and ovarian function suppression is an established first-line treatment for premenopausal patients (pts) with HR+, HER2– ABC, in some cases first-line CT is administered before ET. In the Phase 3 MONALEESA-7 trial (NCT02278120), RIB + TAM/NSAI and goserelin significantly prolonged progression-free survival (PFS) vs placebo (PBO) + TAM/NSAI and goserelin in premenopausal pts with HR+, HER2– ABC. Here, we report results in pts with and without prior CT for ABC. Methods: 672 pts with ≤1 line of prior CT and no prior ET for ABC were randomized 1:1 to RIB (600 mg/day, 3-weeks-on/1-week-off) or PBO + TAM (20 mg/day) or an NSAI (letrozole [2.5 mg/day] or anastrozole [1 mg/day]) and goserelin (3.6 mg every 28 days). The primary endpoint was PFS. Secondary endpoints included overall response rate (ORR) and safety. Prespecified subgroup analyses were performed in pts with and without prior CT for ABC. Results: 47 (14%) pts in each arm had received prior CT for ABC. The most common reason for treatment discontinuation in the RIB vs PBO arm was disease progression (prior CT: 47% vs 55%; no prior CT: 35% vs 51%). Median PFS was increased in the RIB vs PBO arm both in pts with prior CT (16.6 vs 9.0 months; hazard ratio: 0.547; 95% confidence internal [CI]: 0.314–0.954) and without prior CT (24.7 vs 14.5 months; hazard ratio: 0.566; 95% CI: 0.443–0.724). In pts with measurable disease (n = 559), the ORR was 32% vs 27% for those with prior CT (RIB vs PBO arm; P= 0.262) and 54% vs 38% for those with no prior CT (P= 2.90×10^–4). Common all-grade adverse events (≥35% of pts in either arm; RIB vs PBO arm) were neutropenia (prior CT: 77% vs 4%; no prior CT: 76% vs 8%), leukopenia (prior CT: 36% vs 4%; no prior CT: 31% vs 6%), and hot flash (prior CT: 23% vs 36%; no prior CT: 36% vs 33%). Conclusions: Although pt numbers were small, those with prior CT had a numerically shorter PFS and lower ORR vs pts with no prior CT. However, consistent treatment benefit with RIB + TAM/NSAI vs PBO + TAM/NSAI was observed in premenopausal pts with HR+, HER2– ABC, regardless of prior CT for ABC. Clinical trial information: NCT02278120