OS Improvement With Addition of CDK4/6 Inhibitor to Endocrine Therapy in Younger Women With Metastatic Breast Cancer

The following article features coverage from the American Society of Clinical Oncology 2019 meeting. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

According to results of the overall survival (OS) analysis of the phase 3 MONALEESA-7 trial, the addition of the CDK4/6 inhibitor, ribociclib, to endocrine therapy significantly improved overall survival (OS) for premenopausal women with advanced hormone receptor (HR)-positive, HER2-negative (HR+/HER2-) breast cancer. The final analysis of the MONALEESA-7 trial was presented at the 2019 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago, Illinois.¹

Younger women with advanced breast cancer are underrepresented in clinical trials despite the fact that the disease tends to be more aggressive in this population compared with older women, noted Sara Hurvitz, MD, medical director of the clinical research unit at UCLA’s Jonsson Comprehensive Cancer Center, Los Angeles, California, who presented the study results.

The MONALEESA-7 trial (ClinicalTrials.gov Identifier: NCT02278120) was a placebo-controlled, double-blind, randomized phase 3 study that evaluated the combination of endocrine therapy (ie, either tamoxifen or a nonsteroidal aromatase inhibitor, in combination with ovarian suppression with goserelin, a gonadotropin-releasing hormone agonist) with either the CDK4/6 inhibitor, ribociclib, or placebo in pre- and perimenopausal women with advanced breast cancer.  Inclusion criteria for study enrollment included no prior endocrine therapy for advanced disease and up to 1 prior chemotherapy regimen in this setting.

“MONALEESA-7 is the only trial to evaluate CDK4/6 inhibitors exclusively in premenopausal women,” commented Dr Hurvitz.

An interim analysis of the results for the primary study end point, progression-free survival (PFS), performed at a median follow-up of 34.6 months, showed a significant PFS benefit for the addition of ribociclib. Of the 672 patients randomly assigned (1:1) to the ribociclib (335 participants) or placebo (337 participants) arms, median PFS was 23.8 months versus 13.0 months for those in the ribociclib and placebo arms, respectively (hazard ratio [HR], 0.55; 95% CI, 0.44-0.69; P <.0001).² Approximately two-thirds of these patients had not received chemotherapy in the (neo)adjuvant setting and only 14% had received prior chemotherapy for advanced disease.

Strikingly, results of the final study analysis, performed at a median follow-up of 42 months, demonstrated a marked improvement in OS, a key secondary study end point, for patients receiving ribociclib, with a median OS of 40.9 months for the placebo arm; median OS was not reached for those receiving ribociclib (HR, 0.712; 95% CI, 0.535-0.948; P =.00973).  

The percentages of patients alive at 42 months were 70.2% and 46.0% of those receiving ribociclib and placebo, respectively. Furthermore, at this point, 65.8% [ribociclib] vs 49.0% [placebo] of patients had not yet received the next subsequent treatment. The median duration of treatment with endocrine therapy with ribociclib or placebo was approximately 2 years and 1 year, respectively.

No new safety signals were observed for patients receiving ribociclib. Specifically, rates of grade 3/4 neutropenia (63.5% vs 4.5%), hepatobiliary toxicity (11% vs 6.8%), and prolonged QT interval (1.8% vs 1.2%) were higher for patients receiving ribociclib compared with those who received a placebo.

“This is the first time a statistically significant improvement in OS has been observed with a CDK4/6 inhibitor in combination with endocrine therapy [versus endocrine therapy alone] in patients with hormone receptor-positive, HER2-negative advanced disease,” concluded Dr Hurvitz.

Read more of Cancer Therapy Advisor‘s coverage of ASCO’s annual meeting by visiting the conference page.

References

1. Hurvitz S, Im S-A, Lu Y-S, et al. Phase III MONALEESA-7 trial of premenopausal patients with HR+/HER2− advanced breast cancer (ABC) treated with endocrine therapy ± ribociclib: Overall survival (OS) results. Presented at: 2019 American Society of Clinical Oncology (ASCO) Annual Meeting; May 31-June 4, 2019; Chicago, IL. Abstract LBA1008.
2. Tripathy D, Im S-A, Colleoni M, et al. Ribociclib plus endocrine therapy for premenopausal women with hormone receptor-positive, advanced breast cancer (MONALEESA-7): a randomised phase 3 trial. Lancet Oncol. 2018;19(7):904-915.