ER and HER 2 expression are positively correlated in HER 2 non-overexpressing breast cancer

Introduction: Estrogen receptor-a (ER) and human epidermal growth factor receptor 2 (HER2) positivity are inversely correlated by standard criteria. However, we investigated the quantitative relation between ER and HER2 expression at both RNA and protein levels in HER2+ve and HER2-ve breast carcinomas. Methods: ER and HER2 levels were assessed with immunohistochemistry (IHC) and (for HER2) fluorescent in situ hybridization (FISH) and by quantitative reverse transcription-polymerase chain reaction (q-RT-PCR) in formalin-fixed primary breast cancers from 448 patients in the National Cancer Research Institute (NCRI) Adjuvant Breast Cancer Trial (ABC) tamoxifen-only arm. Relations at the RNA level were assessed in 1,139 TransATAC tumors. Results: ER and HER2 RNA levels were negatively correlated as expected in HER2+ve (IHC 3+ and/or FISHamplified) tumors (r = -0.45; P = 0.0028). However, in HER2-ve tumors (ER+ve and ER-ve combined), a significant positive correlation was found (r = 0.43; P < 0.0001), HER2 RNA levels being 1.74-fold higher in ER+ve versus ER-ve tumors. This correlation was maintained in the ER+veHER2-ve subgroup (r = 0.24; P = 0.0023) and confirmed in this subgroup in 1,139 TransATAC tumours (r = 0.25; P < 0.0001). The positive relation extended to IHC-detected ER in ABC: mean ± 95% confidence interval (CI) H-scores were 90 ± 19 and 134 ± 19 for 0 and 1+ HER2 IHC categories, respectively (P = 0.0013). A trend toward lower relapse-free survival (RFS) was observed in patients with the lowest levels of ER and HER2 RNA levels within the ER+veHER2-ve subgroup both for ABC and TransATAC cohorts. Conclusions: ER and HER2 expression is positively correlated in HER2-ve tumors. The distinction between HER2+ve and HER2-ve is greater in ER-ve than in ER+ve tumors. These findings are important to consider in clinical trials of anti-HER2 and anti-endocrine therapy in HER2-ve disease. Trial Registration: Clinical trial identifier: ISRCTN31514446. Introduction Estrogen receptor-a (ER) and the human epidermal growth factor receptor 2 (HER2) are the two key biomarkers that segregate the most distinct biologic subgroups of breast cancer and presently direct adjuvant treatment of primary disease. ER is expressed in approximately 80% of all breast cancers [1]. Amplification or overexpression of HER2 or both are present in about 15% of breast cancers [2,3]. The importance of these receptors as predictive biomarkers has been underpinned by the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP), who have issued guidelines for their accurate testing [4,5]. In HER2-overexpressing (HER2+ve) metastatic cancer, treatment with trastuzumab in combination with chemotherapy improves time to progression and survival [6]. In the adjuvant setting, sequential or concurrent trastuzumab improves disease-free survival and, in some trials, overall survival [7-9]. Despite its recognized benefit in HER2+ve disease, some evidence suggests this benefit also extends to HER2-non-overexpressing/normal (HER2-ve) cancer. Paik and colleagues [10] showed that patients with normal HER2 copy number and protein * Correspondence: Mitch.Dowsett@icr.ac.uk Academic Department of Biochemistry, The Royal Marsden Hospital, Fulham Road, London, SW3 6JJ, UK Full list of author information is available at the end of the article Pinhel et al. Breast Cancer Research 2012, 14:R46 http://breast-cancer-research.com/content/14/2/R46 © 2012 Dowsett et al.; (Should this be Pinhel et al?) licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. levels lower than 3+ by immunohistochemistry (IHC) may also benefit from trastuzumab. The NSABP B-47 (NCT 01275677) trial is now recruiting women with node-positive or high-risk node-negative HER2-low (IHC 1+ or IHC 2+ FISH-ve) invasive breast cancer to address these observations prospectively. HER2 overexpression is associated with partial resistance to endocrine treatment [11-15]. The complex cross-talk between ER and HER2 pathways might be an underlying cause of resistance, although the intrinsic biologic mechanism is poorly understood [16,17]. Some aspects of the relation between ER and HER2 expression have been described previously. ER and HER2 positivity are inversely correlated [18-20], leading to approximately 10% of ER+ve tumors being HER2+ve [21] and about 50% of HER2+ve being ER+ve [22]. ER expression has also been shown to be quantitatively higher in HER2-ve than in HER2+ve tumors among ER+ve tumors; however, few analyses have been conducted on the quantitative relation within the HER2-ve subgroup [23]. In addition, little evidence exists for the biologic importance of IHC 1+ versus 0 levels of HER2 expression, with both categories currently classified as HER2ve. It is unclear whether IHC 1+ cases arise as an artifact of staining or reflect a true difference in expression [10]. Furthermore, few data examine the relation between transcript levels and protein expression by IHC for HER2, even though this relation is well documented for ER [24]. We have therefore (a) characterized gene expression, protein, and/or amplification levels for ER and HER2 individually; (b) explored the relation between ER and HER2 at both the protein and RNA levels, irrespective of the samples ER and HER2 status; and (c) evaluated the significance of transcript levels within the HER2-ve population and, in particular, the ER+veHER2-ve/subgroup in terms of relapse-free survival in a set of 448 early breast cancers from the NCRI Adjuvant Breast Cancer (ABC) Trial-Tamoxifen Late Relapse Study [25,26]. Materials and methods