Abstract GS6-02: The benefit of abemaciclib in prognostic subgroups: An exploratory analysis of combined data from the MONARCH 2 and 3 studies

Abstract

Background: Abemaciclib is an orally administered, selective inhibitor of cyclin-dependent kinases 4 & 6 that is dosed on a twice daily continuous schedule. Abemaciclib has demonstrated clinical efficacy with a generally tolerable safety profile in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer in combination with fulvestrant in MONARCH 2 (NCT02107703) and in combination with non-steroidal aromatase inhibitors (NSAI) in MONARCH 3 (NCT02246621). These analyses were conducted to evaluate if patient and disease characteristics may better inform in whom and when abemaciclib should be initiated to define optimal treatment strategies. Methods: MONARCH 2 and 3 enrolled patients with HR+, HER2- advanced breast cancer. In MONARCH 2, patients whose disease had progressed while receiving endocrine therapy were treated with abemaciclib/placebo plus fulvestrant. In MONARCH 3, patients were treated with abemaciclib/placebo plus NSAI as initial therapy for advanced disease. An exploratory pooled analysis of the two studies was performed to determine significant prognostic factors. Efficacy results (progression-free survival [PFS] and objective response rate [ORR] in patients with measurable disease) were examined for patient subgroups corresponding to each of the identified significant prognostic factors. Subpopulation treatment effect pattern plot (STEPP) methodology was performed to examine the association between treatment-free interval (TFI) following adjuvant endocrine therapy and outcomes of endocrine therapy alone or in combination with abemaciclib in MONARCH 3. Results: Analyses of clinical factors in over 1000 patients confirmed the following to have prognostic value: bone-only disease, liver metastases, tumor grade, progesterone receptor (PgR) status, and ECOG performance status. Prognosis was poor in patients with liver metastases, PgR-negative tumors, and high-grade tumors. While all subpopulations benefited from the addition of abemaciclib to endocrine therapy regardless of prognosis, substantial benefit of abemaciclib was observed in poor prognosis subgroups, characterized by large increases in PFS (hazard ratios = 0.4 to 0.5) and ORR (over 30%). In addition, STEPP analysis of TFI on a subset of the MONARCH 3 population showed that patients with the shortest TFI appeared to have a poorer prognosis and received more benefit from the addition of abemaciclib compared to patients with longer TFI. Conclusions: This exploratory analysis has provided data that could help optimize treatment strategies by identifying that patients with poor prognostic factors may receive greater benefit from the addition of abemaciclib to endocrine therapy. Citation Format: Goetz MP, O'Shaughnessy J, Sledge Jr. GW, Martin M, Lin Y, Forrester T, Mockbee C, Smith IC, Di Leo A, Johnston S. The benefit of abemaciclib in prognostic subgroups: An exploratory analysis of combined data from the MONARCH 2 and 3 studies [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr GS6-02.

A paradigm shift for the treatment of hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer: a review of CDK inhibitors

“…A combined analysis of MONARCH-2 and MONARCH-3 presented at the San Antonio Breast Cancer Symposium in 2017 found that patients with progression after more than 3 years after adjuvant endocrine therapy completion and patients with bone-only metastatic disease might receive only a modest benefit of abemaciclib plus ET versus ET-alone. 28 , 29 …”

Updates on the CDK4/6 Inhibitory Strategy and Combinations in Breast Cancer

“…The impact of clinical factors as predictors of responsiveness to abemaciclib was investigated by a combined analysis of MONARCH-2 and MONARCH-3 studies including over 1000 patients 83 . This analysis confirmed the following factors to have a prognostic value: liver metastases, boneonly disease, tumor grade, progesterone receptor (PR) expression, and ECOG performance status.…”

“…The analysis showed that subgroups of patients who had a poor prognosis benefited the most from abemaciclib, and such an improvement was characterized by an improvement of mPFS (HR: 0.4 to 0.5) and ORR (more than 30%). Therefore, such clinical factors are an indicator that may help to guide clinicians to add abemaciclib to endocrine therapy 83 .…”

NCCN Guidelines Updates: Breast Cancer

“…Unfortunately, it has not been possible to identify subsets who will not benefit from the addition of CDK4/6 inhibitors, as reported from an analysis of MONARCH 3 (Figure 1). 16 "Benefit was seen in all subsets, but what was interesting was that the worse the prognosis, based on clinical features, the bigger the gain from the addition of the CDK4/6 inhibitor," he noted. "This may suggest there is a group who are particularly likely to benefit.…”