Abstract PD2-08: Gene expression analysis and association with treatment response in postmenopausal patients with hormone receptor-positive, HER2-negative advanced breast cancer in the MONALEESA-3 study

Background: In the Phase III MONALEESA-3 study (NCT02422615),the cyclin-dependent kinase (CDK) 4/6 inhibitor ribociclib(RIB) + fulvestrant significantly prolonged progression-free survival (PFS) vs placebo (PBO) + fulvestrant in postmenopausal patients (pts) with hormone receptor–positive, human epidermal growth factor receptor 2–negative (HR+/HER2−) advanced breast cancer (ABC; median, 20.5 vs 12.8 mo; hazard ratio 0.593 [95% CI, 0.480-0.732]; P Methods: Postmenopausal pts with ≤1 prior line of ET for advanced disease were enrolled and randomized 2:1to receive either RIB or PBO plus fulvestrant. Gene expression data were generated for 531 patients using tumor samples collected before treatment using the NanoString 800-gene nCounter® GX Customized Panel. Correlations between PFS and mRNA expression levels were assessed for various genes, including those relevant to breast cancer, the CDK4/6 pathway, the mitogen-activated protein kinase (MAPK) pathway, receptor tyrosine kinases (RTKs), estrogen receptor (ER) signaling and response to estrogen, and proliferation; specific genes are listed in the Table. Pts were classified into low and high mRNA expression subgroups, with median values of gene expression levels or pathway scores as the cutoff. The Kaplan-Meier method was used to calculate median PFS with 95% CIs in each treatment arm by biomarker subgroup. Cox proportional hazards models were used to estimate hazard ratios and 95% CIs. Results: PFS hazard ratios for all biomarker subgroups favored RIB + fulvestrant vs PBO + fulvestrant (Table). There appeared to be a trend toward greater PFS benefit with RIB in patients with lower expression of BCL2 or genes involved in ER signaling. Similar RIB PFS benefit was observed regardless of the expression level of the CCNE1 gene, RTK genes, genes involved in tumor cell proliferation, CDK4/6 pathway genes, or MAPK pathway genes. Conclusions: The PFS benefit observed with RIB vs PBO across gene expression subgroups in this analysis was generally consistent with that seen in the primary analysis of MONALEESA-3. Citation Format: Stephen Chia, Faye Su, Patrick Neven, Seock-Ah Im, Katarina Petrakova, Giulia Val Bianchi, Wei He, Karen Rodriguez-Lorenc, Tetiana Taran, Naveen Babbar, Dennis Slamon. Gene expression analysis and association with treatment response in postmenopausal patients with hormone receptor-positive, HER2-negative advanced breast cancer in the MONALEESA-3 study [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr PD2-08.