NeoPalAna: Neoadjuvant Palbociclib, a Cyclin-Dependent Kinase 4/6 Inhibitor, and Anastrozole for Clinical Stage 2 or 3 Estrogen Receptor-Positive Breast Cancer

Abstract

Purpose: Cyclin-dependent kinase (CDK) 4/6 drives cell proliferation in estrogen receptor-positive (ER⁺) breast cancer. This single-arm phase II neoadjuvant trial (NeoPalAna) assessed the antiproliferative activity of the CDK4/6 inhibitor palbociclib in primary breast cancer as a prelude to adjuvant studies.Experimental Design: Eligible patients with clinical stage II/III ER⁺/HER2^- breast cancer received anastrozole 1 mg daily for 4 weeks (cycle 0; with goserelin if premenopausal), followed by adding palbociclib (125 mg daily on days 1-21) on cycle 1 day 1 (C1D1) for four 28-day cycles unless C1D15 Ki67 > 10%, in which case patients went off study due to inadequate response. Anastrozole was continued until surgery, which occurred 3 to 5 weeks after palbociclib exposure. Later patients received additional 10 to 12 days of palbociclib (Cycle 5) immediately before surgery. Serial biopsies at baseline, C1D1, C1D15, and surgery were analyzed for Ki67, gene expression, and mutation profiles. The primary endpoint was complete cell cycle arrest (CCCA: central Ki67 ≤ 2.7%).Results: Fifty patients enrolled. The CCCA rate was significantly higher after adding palbociclib to anastrozole (C1D15 87% vs. C1D1 26%, P < 0.001). Palbociclib enhanced cell-cycle control over anastrozole monotherapy regardless of luminal subtype (A vs. B) and PIK3CA status with activity observed across a broad range of clinicopathologic and mutation profiles. Ki67 recovery at surgery following palbociclib washout was suppressed by cycle 5 palbociclib. Resistance was associated with nonluminal subtypes and persistent E2F-target gene expression.Conclusions: Palbociclib is an active antiproliferative agent for early-stage breast cancer resistant to anastrozole; however, prolonged administration may be necessary to maintain its effect. Clin Cancer Res; 23(15); 4055-65. ©2017 AACR.

Fig 1. Ki67 response by PIK3CA mutation status (A-C), luminal subtype (D-F) and with/without Cycle 5 (G-I)

Box plots of all evaluable samples of indicated cohort (A, D, G) and Ki67 of individual tumors (B-C, E-F, H-I) are shown. *p<0.005 comparing Ki67 values with that of the previous time-point in the corresponding cohort. Line colors in the Ki67 graphs denote response category (Anastrozole Sensitive, C1D1 Ki67<2.7%; Palbociclib Sensitive, C1D1 Ki67≤2.7% and C1D15 Ki67<2.7%; Resistant, C1D15 Ki67≤2.7%).

Fig 2. Somatic mutation, intrinsic subtype and clinicopathological characteristics of individual tumors in relation to Ki67 response

Genes with mutations detected in at least 2 samples are shown. Mutation frequency, number of tier 1 mutations.

Fig 3. Microarray gene expression analysis

A, Venn-diagram of the number of genes significantly changed (Benjamini-Hochberg false discovery rate adjusted F test P≤0.05) between time-points. B, Heatmap of the 6 genes significantly down-regulated by anastrozole and by adding palbociclib. C, Top 20 significantly altered Go pathways comparing the gene expression profiles between C1D1 and C0D1, or between surgery and C1D15. % indicates the percentage of genes observed in the indicated GO pathway.

Fig 4. Boxplots of gene expression levels of CCND3, CCNE1, and CDKN2D by Ki67 response and by time-point

Significant p-values by pairwise two sample t-test were indicated. The sample sizes for anastrozole sensitive, palbociclib sensitive, and resistant groups were 6, 18, and 5 at C0D1, 6, 21, and 3 at C1D1, 5, 20, and 3 at C1D15, and 3, 17, 1 at surgery time-points, respectively.