Abstract P2-09-16: Tumor infiltrating lymphocytes (TILs) as a biomarker for resistance to palbociclib (Pal) in the NeoPalAna trial
Authors: Sanati S , Barve R , Luo J , Hoog J , Head R , Ellis M , Ma C 
Published: February 2018

Background: Cyclin-dependent kinase (CDK) 4/6 inhibitors improve disease free survival for patients (pts) with advanced hormone receptor positive (HR+) and HER2 negative (HER2-) breast cancer (BC). However, there are no established biomarkers that identify sensitive versus resistant tumors. We have recently reported results from the phase II neoadjuvant NeoPalAna trial (NCT01723774 ) which demonstrated that Pal enhanced the anti-proliferative activity when added to anastrozole (Ana) monotherapy in HR+HER2- BC. Interestingly, a small group of pts (15%) were resistant to Pal, exhibiting persistent tumor cell proliferation (Ki67 &gt;2.7%) on Ana plus Pal. Several studies have evaluated the prognostic and predictive importance of TILs in BC, particularly in triple negative and HER2+ subtypes. Studies evaluating TILs in HR+ BC is limited. Here we evaluated the utility of TILs in identifying Pal-resistant tumors.

Methods: Serial biopsies were collected from pts at 4 time points: baseline (BL), cycle 1 day 1 (C1D1) following 28 days of Ana monotherapy, cycle 1 day 15 (C1D15) at 2 weeks post the addition of Pal, and at surgery (Surg). TILs were evaluated using published recommendations by the TILs international working group. Agilent 4X44 whole genome gene expression arrays performed on fresh frozen biopsies at BL, C1D1, and C1D15 were analyzed for pathways and gene signatures that differentiate Pal-resistant (Pal-r) (C1D15 Ki67 &gt;2.7%) from Ana-sensitive (Ana-s) (C1D1 Ki67 ≤2.7%) or Pal- sensitive (Pal-s) (C1D1 Ki67 &gt;2.7% but C1D15 Ki67 ≤2.7%) tumors defined by Ki67 response. TILs at each time point were pairwise compared between response groups using Wilcoxon rank sum test and Benjamini-Hochberg adjusted two-sided p-values were reported. Change between 2 time points within a response group was evaluated by Wilcoxon signed rank test.

Results: The TILs were significantly different between Ana-s and Pal-s groups [BL p=0.03, C1D1 p=0.01, C1D15 p=.02], as well as between Ana-s and Pal-r groups [BL p=0.03, C1D1 p=0.04, C1D15 p=0.02]. Overall Pal-r samples showed the highest TILs at all time points, while Ana-s samples showed the lowest TILs. There was no significant change between time points.

Elevated TILs in Pal-r group was further supported by microarray gene expression analysis which demonstrated a large group of genes associated MHC Class-I (15+ HLA and proteasome genes) as well as Immune–inflammation pathways (18+ T cell & lymphocyte markers, signaling genes) being up regulated at BL in the Pal-r group (n=5). Pal-r samples showed a similar trend in subsequent time points although the numbers of samples were small. Many genes within this immune-inflammatory group of genes were correlated with Ki67 change at C1D15 from BL, suggestive of a potential relationship with resistance.

Conclusions: Our data shows Pal resistance was consistently associated with higher TILs at BL and post treatment, which correlated with increased expression of inflammation-immune group genes. TILs may have utility to be used as a biomarker to identify Pal resistant BC. Our data is hypothesis generating and raises the possibility of immune therapy to overcome Pal resistance in BC.

Citation Format: Sanati S, Barve R, Luo J, Hoog J, Head R, Ellis M, Ma C. Tumor infiltrating lymphocytes (TILs) as a biomarker for resistance to palbociclib (Pal) in the NeoPalAna trial [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 P2-09-16.