Abstract A9: The cocaine and amphetamine-regulated transcript (CART) is an independent prognostic factor in lymph node-negative breast cancer and predicts outcome in tamoxifen treated patients

Abstract

Abstract The successful identification and translation of informative biomarkers to aid clinical decision making is central to the effective implementation of personalized cancer therapeutic regimens. Antibody-based proteomics occupies a pivotal space in the cancer biomarker discovery and validation pipeline, facilitating the high-throughput evaluation of candidate markers. We have applied this approach to identify the cocaine- and amphetamine-regulated transcript (CART) as an independent poor prognostic marker in early stage breast cancer. The management of lymph node-negative breast cancer is the subject of much debate and two large ongoing clinical trials with particular emphasis on the requirement for adjuvant chemotherapy. Here we demonstrate, by tissue microarray and automated image analysis using a consistently applied threshold for definition of CART levels (median intensity +/− 1 standard deviation), that the neuropeptide hormone CART is expressed in primary and metastatic breast cancer and is an independent poor prognostic factor in ER-positive (p=0.0003), lymph node-negative (p=0.0025) tumors in two large breast cancer cohorts (n>1000). Kaplan-Meier analysis and the log rank test were used to illustrate differences between overall survival (OS) and recurrence free survival (RFS) according to CART protein and mRNA expression. Cox regression proportional hazards models were used to estimate the relationship between outcome and CART expression, grade, age, nodal status, ER status, PR status, Her2, Ki-67 and tumor size. We also show that CART mediates an autocrine/paracrine effect leading to an amplification of the CART signal in breast cancer cells. Furthermore, we additionally demonstrate that CART increases the transcriptional activity of ERα in a ligand-independent manner via the mitogen-activated protein kinase (MAPK) pathway and that CART-High tumors express increased levels of ER-target genes. Finally, we show that ectopic expression of CART in two independent ER+ cell lines protects against tamoxifen-mediated cell death (p=0.025) and that high CART expression predicts outcome in 3 independent tamoxifen-treated cohorts (p=0.002). We clearly demonstrate that both pre- and postmenopausal patients with CART-positive tumors have a poor prognosis and are resistant to tamoxifen and therefore should receive aggressive adjuvant chemotherapy. We believe that CART profiling will facilitate stratification of lymph node-negative breast cancer patients into high- and low-risk categories and allow the personalization of therapy.