Impact of ribociclib (RIB) dose modifications (mod) on overall survival (OS) in patients (pts) with HR+/HER2- advanced breast cancer (ABC) in MONALEESA(ML)-2

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Background: The phase 3 ML-2, -3, and -7 trials all demonstrated consistent and statistically significant OS benefit with RIB (starting dose: 600 mg/d 3 wk on/1 wk off) vs PBO in pts with HR+/HER2− ABC. RIB dose mod (reductions and/or interruptions) when needed did not impact OS benefit with RIB + endocrine therapy (ET) in previous analyses of ML-3/-7. Here we present data on the effect of RIB dose mod on OS in postmenopausal pts with HR+/HER2− ABC in ML-2. Methods: ML-2 (NCT01958021) enrolled postmenopausal pts randomized 1:1 to first-line RIB + letrozole (LET) or PBO + LET. Landmark (LM) analyses of OS were performed to evaluate the association between dose reductions (yes vs no) and OS. Multiple LM times were considered to determine the sensitivity of the findings. As an alternative to LM analysis, a Cox proportional hazards model with a time-varying covariate was performed. Two time-dependent variables, dose reduction (with/without mod from 600 mg starting dose) and relative dose intensity 2 (RDI2), were included in the respective model as covariates to explore the association with OS. To account for differences in time to first dose mod, RDI2 reflects the post–dose mod period. Median (m) OS was obtained using a modified Kaplan-Meier method. Results: At data cutoff (June 10, 2021; m follow-up, 49.35 [range, 0-86.7] mo), 209 of 334 pts (62.6%) had ≥ 1 RIB dose reduction and 125 of 334 (37.4%) had 0 RIB dose reduction. LM analyses by dose reduction are presented (Table). mOS was 66.0 (95% CI, 57.6-75.7) mo in pts with ≥ 1 RIB dose reduction vs 60.6 (95% CI, 42.5-79.2) mo in pts with no RIB dose reductions (HR, 0.87 [95% CI, 0.65-1.18]). RDI2 was classified according to tertile: low (< 64.27%), medium (64.27%-95.86%), and high (> 95.86%). In pts with low, medium, and high RDI2, mOS was 62.6 (95% CI, 50.0-80.7) mo, 63.9 (95% CI, 48.8-not reached [NR]) mo, and 65.3 (95% CI, 50.5-NR) mo, respectively (HR low vs high, 0.99 [95% CI, 0.69-1.42]; HR medium vs high, 0.97 [95% CI, 0.62-1.38]). Conclusions: In this exploratory analysis of ML-2, OS benefit was maintained in pts with HR+/HER2− ABC who required mod from the recommended starting dose of RIB (600 mg/d 3 wk on/1 wk off). No relationship was observed between OS and RIB dose reduction or RDI2; OS benefit with RIB was observed in all groups. Clinical trial information: NCT01958021. [Table: see text]

Overall Survival with Ribociclib plus Letrozole in Advanced Breast Cancer

BACKGROUND

In a previous analysis of this phase 3 trial, first-line ribociclib plus letrozole resulted in significantly longer progression-free survival than letrozole alone among postmenopausal patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer. Whether overall survival would also be longer with ribociclib was not known.

METHODS

Here we report the results of the protocol-specified final analysis of overall survival, a key secondary end point. Patients were randomly assigned in a 1:1 ratio to receive either ribociclib or placebo in combination with letrozole. Overall survival was assessed with the use of a stratified log-rank test and summarized with the use of Kaplan-Meier methods after 400 deaths had occurred. A hierarchical testing strategy was used for the analysis of progression-free survival and overall survival to ensure the validity of the findings.

RESULTS

After a median follow-up of 6.6 years, 181 deaths had occurred among 334 patients (54.2%) in the ribociclib group and 219 among 334 (65.6%) in the placebo group. Ribociclib plus letrozole showed a significant overall survival benefit as compared with placebo plus letrozole. Median overall survival was 63.9 months (95% confidence interval [CI], 52.4 to 71.0) with ribociclib plus letrozole and 51.4 months (95% CI, 47.2 to 59.7) with placebo plus letrozole (hazard ratio for death, 0.76; 95% CI, 0.63 to 0.93; two-sided P = 0.008). No new safety signals were observed.

CONCLUSIONS

First-line therapy with ribociclib plus letrozole showed a significant overall survival benefit as compared with placebo plus letrozole in patients with HR-positive, HER2-negative advanced breast cancer. Median overall survival was more than 12 months longer with ribociclib than with placebo. (Funded by Novartis; MONALEESA-2 ClinicalTrials.gov number, NCT01958021.).

Abstract GS2-01: Overall survival subgroup analysis by metastatic site from the phase 3 MONALEESA-2 study of first-line ribociclib + letrozole in postmenopausal patients with advanced HR+/HER2− breast cancer

Background: MONALEESA-2 (ML-2) recently reported a statistically significant overall survival (OS) benefit with first-line ribociclib (RIB) + letrozole (LET) over placebo (PBO) + LET in postmenopausal patients with HR+/HER2- advanced breast cancer (ABC) (median, 63.9 vs 51.4 months; hazard ratio, 0.76; 95% CI, 0.63-0.93; P = .004). Understanding OS outcomes in clinically relevant subgroups of patients is important for improving personalized care and prognosis. Here, we report the results of a prespecified exploratory OS analysis in select patient subgroups by baseline location and number of metastatic sites.. Methods: Postmenopausal patients with HR+/HER2− ABC were randomized 1:1 to receive first-line RIB or PBO with LET. Prespecified exploratory OS analyses were performed for subgroups of special interest by baseline location (bone only [yes or no], liver involvement [yes or no], liver or lung involvement [yes or no]) and number of metastatic sites (&lt; 3 or ≥ 3). The data are hypothesis generating since this analysis was exploratory and not powered for statistical significance.. Results: A total of 668 patients were included in the analysis. A consistent improvement in OS was observed with RIB + LET vs PBO + LET in all subgroups regardless of baseline metastatic site (Table). RIB + LET demonstrated an OS benefit over PBO + LET in clinically relevant subgroups by baseline location and number of metastatic sites, including subgroups of patients with liver metastases, liver or lung metastases, and ≥ 3 metastatic sites, who generally have a worse prognosis.. Conclusion: Consistent with the intent-to-treat population of ML-2, the results of this prespecified exploratory analysis demonstrated an OS benefit with RIB + LET independent of the site and number of metastatic lesions.

TableTreatment Arm (n)HR (95% CI)Bone-only metastasisYesRIB + LET (69)0.78 (0.50-1.21)PBO + LET (79)NoRIB + LET (265)0.77(0.61-0.96)PBO + LET (255)Liver involvementYesRIB + LET (59)0.81 (0.54-1.24)PBO + LET (72)NoRIB + LET (275)0.77 (0.62-0.97)PBO + LET (262)Liver or lung involvementYesRIB + LET (182)0.81(0.62-1.05)PBO + LET (190)NoRIB + LET (152)0.71 (0.53-0.96)PBO + LET (144)No. of metastatic sites&lt; 3RIB + LET (220)0.78(0.61-1.00)PBO + LET (222)≥ 3RIB + LET (114)0.71(0.51-0.98)PBO + LET (112)

Citation Format: Joyce O'Shaughnessy, Salomon M Stemmer, Howard A Burris, Yoon-Sim Yap, Gabe Sonke, Lowell Hart, Mario Campone, Katarina Petrakova, Eric P Winer, Wolfgang Janni, Pierfranco Conte, David A Cameron, Fabrice André, Carlos Arteaga, Juan Pablo Zarate, Arunava Chakravartty, Tetiana Taran, Fabienne Le Gac, Paolo Serra, Gabriel N Hortobagyi. Overall survival subgroup analysis by metastatic site from the phase 3 MONALEESA-2 study of first-line ribociclib + letrozole in postmenopausal patients with advanced HR+/HER2− breast cancer [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 GS2-01.

First-line (1L) ribociclib (RIB) plus letrozole (LET) for postmenopausal women with hormone receptor-positive (HR+), HER2- advanced breast cancer (ABC): MONALEESA-2 long-term safety results

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Background: In the phase III MONALEESA-2 study (NCT01958021), 1L treatment (Tx) with RIB (cyclin-dependent kinase 4/6 inhibitor) plus LET significantly prolonged PFS vs placebo (PBO) + LET in patients (pts) with HR+/HER2– ABC (HR 0.56; P<0.0001). In the primary publication (data cutoff, Jan 2016), the median duration of exposure was 13.0 mo (RIB + LET) and 12.4 mo (PBO + LET), and the most common all-grade adverse events (AEs) in the RIB + LET arm were neutropenia (74.3%), nausea (51.5%), infections (50.3%), fatigue (36.5%), and diarrhea (35.0%; Hortobagyi GN, et al. N Engl J Med. 2016;375:1738-48). Here we present long-term safety data from MONALEESA-2. Methods: Pts received either RIB + LET (n=334) or PBO + LET (n=330). AEs were graded per CTCAE v4.03. Results: As of data cutoff (Oct 2018), 79 (24%) pts (RIB + LET) and 39 (12%) pts (PBO + LET) remained on Tx. The median duration of exposure was 20.2 mo (range, 0-54) for RIB + LET and 14.1 mo for PBO + LET, and 30% and 17%, respectively, had ≥ 36 mo of exposure. Neutropenia was the most common exposure-adjusted any-grade AE of special interest (AESI) in the RIB + LET arm (Table). AEs were the most common reason for RIB dose reductions (56.6%) and interruptions (73.4%). Discontinuations due to AEs occurred in 19.2% and 4.2% of pts in the RIB + LET and PBO + LET arms, respectively, and the most common AEs leading to discontinuation in the RIB + LET arm were increased ALT (4.5%), GI disorders (3.3%), and increased AST (2.7%). Prolonged QT led to dose interruption in 0.9% of patients (no discontinuations), and the additional follow-up did not reveal any sudden deaths related to prolonged QT interval beyond the 1 identified in the primary analysis. Conclusions: AEs occurring with 1L RIB + LET in postmenopausal pts with HR+/HER2– ABC were manageable and the safety profile was comparable to that in the primary report. Clinical trial information: NCT01958021. [Table: see text]