Abstract P1-18-11: Analysis of first-line (1L) patients (pts) with de novo disease vs late relapse and all pts with vs without prior chemotherapy (CT) in the MONALEESA-3 (ML-3) trial

Background: The phase 3 ML-3 trial demonstrated significant OS benefit for ribociclib (RIB) + fulvestrant (FUL) over placebo (PBO) + FUL as first- or second- line therapy in postmenopausal pts with HR+/HER2- advanced breast cancer (ABC). Prior treatment ([neo]adjuvant or advanced setting) may impact subsequent therapy outcomes, including OS; therefore, understanding the potential effect of prior treatment is of high clinical interest. Here, we present PFS and OS data from 2 subgroup analyses in ML-3: 1L pts with de novo disease vs late relapse and all pts with vs without prior CT. Methods: ML-3 (NCT02422615) enrolled postmenopausal pts who were randomized 2:1 to receive RIB + FUL or PBO + FUL. Pts with prior ET ([neo]adjuvant or ≤1 prior ET for ABC) and no CT for ABC were included. Pts with de novo disease were defined as initially diagnosed as ABC with no prior treatment for ABC. Pts with late relapse were defined as those who relapsed >12 months from completion of (neo)adjuvant ET with no prior treatment for ABC. Since prior CT for ABC was not allowed in ML-3, the prior CT analysis compares pts with prior (neo)adjuvant CT vs those without prior (neo)adjuvant CT. Results: The data cutoff was October 30, 2020. Within the 1L population, in the de novo vs late relapse analysis, 132 pts (RIB: n = 91; PBO: n = 41) had de novo disease, and 153 had late relapse (RIB: n = 98; PBO: n = 55). Baseline characteristics were generally balanced between the de novo and late relapse groups, with some notable exceptions: a higher proportion of pts with de novo disease were aged <65 years (52.3% vs 41.8%) and a lower proportion had visceral disease (53.0% vs 63.4%). In the late relapse group, 70.6% had prior (neo)adjuvant CT. De novo disease or late relapse did not appear to be prognostic as both PFS and OS were generally comparable between those 2 groups among pts treated with RIB or those treated with PBO (Table). Treatment with RIB + FUL demonstrated consistent PFS and OS benefits over PBO + FUL in both pts with de novo disease and those with late relapse. In the prior CT analysis, 391 pts (RIB: n = 265; PBO: n = 126) had prior CT (41.4% in 1L and 55.5% in 2L/early relapse [3.1% data missing]) and 334 (RIB: n = 219; PBO: n = 115) had no prior CT (60.8% in 1L, 38.9% in 2L/early relapse [0.3% data missing]). Baseline characteristics were generally balanced between pts with and without prior CT, with some exceptions: a higher proportion of pts with prior CT were aged <65 years (62.1% vs 42.8%) and had prior ET in any setting (86.4% vs 53.0%). Pts without prior CT had longer median PFS and OS compared with those who had prior CT in both the RIB and PBO arms (OS without vs with prior CT treated with RIB: HR, 0.68 [95% CI, 0.52-0.89]; PBO: HR, 0.72 [95% CI, 0.52-1.00]). Treatment with RIB + FUL demonstrated consistent PFS and OS benefits over PBO + FUL in both pts with prior CT and those without (OS for RIB vs PBO with prior CT: HR, 0.76 [95% CI, 0.58-1.01]; without prior CT: HR, 0.70 [95% CI, 0.50-0.97]). Conclusions: This exploratory analysis demonstrated that metastatic presentation (de novo vs late relapse) was not prognostic for disease outcomes; however, prior CT exposure, even in (neo)adjuvant, was associated with poorer PFS and OS. The addition of RIB showed consistent PFS and OS benefit across all subgroups in this analysis. Particularly, the addition of RIB resulted in a consistent and clinically meaningful PFS and OS benefit with a decrease in relative risk of death by 24% in pts with prior exposure to CT.

RIB + FULPBO + FULHR (RIB vs PBO)De novo/late relapseMedian PFS (95% CI), monthsDe novo35.6. (27.1-42.0)22.1. (14.6-33.1)0.55. (0.35-0.86)Late relapse35.8. (20.0-44.4)22.0. (16.5-27.7)0.60. (0.40-0.89)HR (de novo vs late elapse)0.93. (0.64-1.36)0.996. (0.63-1.57)Median OS (95% CI), monthsDe novo59.9. (52.7-NE)52.9. (39.6-NE)0.67. (0.38-1.19)Late relapseNE. (54.9-NE)52.3. (40.4-NE)0.69. (0.42-1.13)HR (de novo vs late relapse)0.899. (0.552-1.465)0.91. (0.51-1.62)Prior (neo)adjuvant CTMedian PFS (95% CI), monthsWithout prior CT28.3. (23.3-35.6)17.5. (13.6-21.9)0.60. (0.46-0.78)With prior CTa17.9. (14.3-19.9)10.8. (7.2-12.3)0.61. (0.48-0.78)HR (without vs with prior CT)0.76. (0.60-0.94)0.72. (0.55-0.95)Median OS (95% CI), monthsWithout prior CTNE (54.9-NE)44.9 (38.5-58.1)0.70. (0.50-0.97)With prior CTa43.0 (39.1-51.2)40.1 (30.3-48.6)0.76. (0.58-1.01)HR (without vs with prior CT)0.68 (0.52-0.89)0.72 (0.52-1.00)NE, not estimable a Includes 4 patients who received prior CT for ABC (protocol violation).

Citation Format: Michelino De Laurentiis, Matteo Lambertini, Stephen Chia, Hope S Rugo, Katarina Petrakova, Cristian Villanueva, Sara Hurvitz, J. Thaddeus Beck, Agnes Lteif, Sina Haftchenary, Uday Deore, Jiwen Wu, Nagi El-Saghir. Analysis of first-line (1L) patients (pts) with de novo disease vs late relapse and all pts with vs without prior chemotherapy (CT) in the MONALEESA-3 (ML-3) trial [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-18-11.

Ribociclib plus fulvestrant for postmenopausal women with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer in the phase III randomized MONALEESA-3 trial: updated overall survival

BACKGROUND

Ribociclib plus fulvestrant demonstrated significant progression-free survival (PFS) and overall survival (OS) benefits in patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC). Here we present a new landmark in survival follow-up for a phase III cyclin-dependent kinases 4 and 6 inhibitor clinical trial in patients with ABC (median, 56.3 months).

PATIENTS AND METHODS

This phase III, randomized, double-blind, placebo-controlled trial was conducted at 174 sites (30 countries). Patients were men and postmenopausal women (age ≥18 years) with histologically/cytologically confirmed HR+/HER2- ABC. Patients could have received ≤1 line of endocrine therapy (ET) but no chemotherapy for ABC. Patients, assigned 2:1, were stratified by the presence/absence of liver/lung metastases and previous ET. Patients received intramuscular fulvestrant (500 mg, day 1 of each 28-day cycle plus day 15 of cycle 1) with oral ribociclib (600 mg/day, 3 weeks on, 1 week off) or placebo. Efficacy analyses were by intention to treat. Safety was assessed in patients receiving ≥1 dose study treatment. OS was a secondary endpoint. MONALEESA-3 is registered with ClinicalTrials.gov (NCT02422615; no longer enrolling).

RESULTS

Between 18 June 2015 and 10 June 2016, 726 patients were randomly assigned (484, ribociclib; 242, placebo). At data cut-off (30 October 2020), median OS (mOS) was 53.7 months (ribociclib) versus 41.5 months (placebo) [hazard ratio (HR), 0.73; 95% confidence interval (CI) 0.59-0.90]. Subgroup analyses were consistent with overall population. In the first-line setting, most patients in the ribociclib arm (∼60%) lived longer than median follow-up; mOS was 51.8 months in the placebo arm (HR, 0.64; 95% CI 0.46-0.88). In the second-line setting, mOS was 39.7 months (ribociclib) versus 33.7 months (placebo) (HR, 0.78; 95% CI 0.59-1.04). No apparent drug-drug interaction between ribociclib and fulvestrant or new safety signals were observed.

CONCLUSIONS

This analysis reported extended OS follow-up in MONALEESA-3. mOS was ∼12 months longer in patients with HR+/HER2- ABC treated with ribociclib plus fulvestrant compared with fulvestrant monotherapy.

Updated overall survival (OS) results from the phase III MONALEESA-3 trial of postmenopausal patients (pts) with HR+/HER2- advanced breast cancer (ABC) treated with fulvestrant (FUL) ± ribociclib (RIB)

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Background: The Phase III MONALEESA-3 trial (NCT02422615) previously demonstrated a statistically significant improvement in OS with RIB, a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i), plus FUL compared with placebo (PBO) plus FUL as first-line (1L) or second-line (2L) treatment in postmenopausal pts with HR+/HER2− ABC (median, not reached vs 40.0 mo; hazard ratio [HR], 0.72; 95% CI, 0.57-0.92, P =.00455). This analysis was final per the protocol; following the unblinding of the study, pts still on study treatment in the PBO arm were allowed to cross over to the RIB arm. We report an exploratory analysis of OS after an additional median 16.9 mo of follow-up, allowing for further characterization of long-term survival benefits of RIB. Methods: Postmenopausal pts with HR+/HER2− ABC were randomized 2:1 to receive RIB + FUL or PBO + FUL in 1L and 2L settings. Updated OS was evaluated by Cox proportional hazards model and summarized using Kaplan-Meier methods. Additional postprogression endpoints such as progression-free survival 2 (PFS2), time to chemotherapy (CT), and CT-free survival were also evaluated and summarized. Results: At the data cutoff (Oct 30, 2020), the median follow-up was 56.3 mo (min, 52.7 mo) and 68 (14.0%) and 21 (8.7%) patients were still on treatment in the RIB vs PBO arms, respectively. With this extended follow-up, RIB + FUL continued to demonstrate an OS benefit vs PBO + FUL (median, 53.7 vs 41.5 mo; HR, 0.73; 95% CI, 0.59-0.90). RIB + FUL had prolonged OS vs PBO + FUL in the 1L (median, not reached vs 51.8 mo; HR, 0.64; 95% CI, 0.46-0.88) and 2L subgroups (median, 39.7 vs 33.7 mo; HR, 0.78; 95% CI, 0.59-1.04). Subgroup analyses also showed a consistent OS benefit compared with the intent-to-treat (ITT) population for most subgroups. PFS2, time to CT, and CT-free survival for the ITT population favored RIB + FUL (Table). Among pts who discontinued study treatment, 81.9% and 86.4% received a next-line subsequent antineoplastic therapy, while 14.0% and 30.0% received a CDK4/6i as any subsequent line in the RIB vs PBO arms, respectively. No new safety signals were observed. Conclusions: The previously demonstrated robust and clinically meaningful OS benefit with RIB + FUL compared with PBO + FUL was maintained after almost 5 years of follow-up in postmenopausal pts with HR+/HER2− ABC. The OS benefit of RIB was observed in the 1L and 2L subgroups, which further supports the use of RIB in these populations. The results also demonstrated a significant delay in the use of subsequent CT with RIB vs PBO. Clinical trial information: NCT02422615 .[Table: see text]