The anti-oestrogen tamoxifen is the most commonly used treatment for patients with oestrogen-receptor (ER)-positive breast cancer. Although many patients benefit from tamoxifen in the adjuvant and metastatic settings, resistance is an important clinical problem. The target of tamoxifen in vivo is the ER. Over the last decade many advances have been made in our understanding of the biology of the ER which may help to explain how resistance to tamoxifen develops. Such mechanisms may include changes in the expression of ERα or ERβ, alterations in co-regulatory proteins, and the influences of cellular kinase signal transduction pathways. The experimental and clinical evidence supporting these mechanisms of tamoxifen resistance are discussed in this review.
Alistair Ring and Mitch Dowsett
Anne Kendall and Mitch Dowsett
Aromatase inhibitors (AIs) have a proven role in the treatment of early and metastatic breast cancer. The success of tamoxifen in reducing the relative risk of developing hormone-sensitive breast cancer in chemoprevention trials has been hampered by their long-term toxicity profile. AIs have the potential to further reduce rates of breast cancer in high-risk postmenopausal women. This article reviews the evidence to support the potential efficacy of AIs in the chemoprevention setting. It particularly focuses on a discussion of novel concepts of utilising AIs, so that they reduce breast cancer risk while minimising systemic toxicity, and highlights the importance of accurately developing risk prediction algorithms.
Marion T Weigel and Mitch Dowsett
Breast cancer treatment has experienced several changes in the past decades due to the discovery of specific prognostic and predictive biomarkers that enable the application of more individualized therapies to different molecular subgroups. These subgroups show specific differences regarding biological clinical behavior. In addition to the classical clinical prognostic factors of breast cancer, established molecular biomarkers such as estrogen receptor and progesterone receptor have played a significant role in the selection of patients benefiting from endocrine therapy for many years. More recently, the human epidermal growth factor receptor 2 (HER2) has been validated to be not only a prognostic factor, but also a predictor of response to HER2 targeting therapy. The shift toward an earlier diagnosis of breast cancer due to improved imaging methods and screening programs highlights the need for new factors and combinations of biomarkers to quantify the residual risk of patients and to indicate the potential value of additional treatment strategies. The marker of proliferation Ki67 has recently emerged as an important marker due to several applications in neoadjuvant therapy in addition to its moderate prognostic value. With the introduction of high-throughput technologies, numerous multigene signatures have been identified that aim to outperform traditional markers: current prospective clinical trials are seeking evidence for their definitive role in breast cancer. There exist many more factors and approaches that have the potential to become relevant in the near future including the detection of single disseminating and circulating tumor cells in blood and bone marrow as well as of circulating cell-free DNA and microRNA. Careful randomized prospective testing and comparison with existing established factors will be required to select those emerging markers that offer substantial cost-effective benefit and thereby justify their routine use for breast cancer therapy decision-making.
Lesley-Ann Martin, Ian Farmer, Stephen R D Johnston, Simak Ali and Mitch Dowsett
The knowledge that steroids play a pivotal role in the development of breast cancer has been exploited clinically by the development of endocrine treatments. These have sought to perturb the steroid hormone environment of the tumour cells, predominately by withdrawal or antagonism of oestrogen. Unfortunately, the beneficial actions of existing endocrine treatments are attenuated by the ability of tumours to circumvent the need for steroid hormones, whilst in most cases, retaining the nuclear steroid receptors. The mechanisms involved in resistance to estrogen deprivation are of major clinical relevance for optimal treatment of breast cancer patients and the development of new therapeutic regimes. We have shown that long-term culture of MCF7 cells in medium depleted of oestrogen (LTED) results in hypersensitivity to oestradiol (E2) coinciding with elevated levels of both ERα phosphorylated on Ser118 and ERK1/ERK2. Our data suggest elevated ERK1/ERK2 activity results wholly or in part from enhanced ERBB2 expression in the LTED cells. These cells showed greater sensitivity to the tyrosine kinase inhibitor ZD1839 in both ERα-mediated transcription and growth assays compared with the wt-MCF7. Similarly the MEK inhibitor U0126 decreased basal ERα-mediated transcription and proliferation in the LTED cells by 50% and reduced their sensitivity to the proliferative effects of E2 10-fold, whilst having no effect on the wild type (wt). However, complete suppression of ERK1/ERK2 activity in the LTED cells did not inhibit ERα Ser118 phosphorylation suggesting that the cells remained ligand-dependent. This was further confirmed by the increased sensitivity of the LTED cells to the growth suppressive effects of ICI 182,780 and suggested that the LTED cells remained wholly or partially dependent on oestrogen receptor (ER)/oestrogen responsive elements directed growth. These findings suggest that treatments targeted at growth factor signalling pathways may be useful in patients acquiring resistance to oestrogen deprivation with aromatase inhibitors and that the pure anti-oestrogen ICI 182,780 may also be effective by blocking or destabilizing ER and hence disrupting cross-talk.
Sunil Pancholi, Anne E Lykkesfeldt, Caroline Hilmi, Susana Banerjee, Alexandra Leary, Suzanne Drury, Stephen Johnston, Mitch Dowsett and Lesley-Ann Martin
Acquired resistance to endocrine therapies remains a major clinical obstacle in hormone-sensitive breast tumors. We used an MCF-7 breast tumor cell line (TamR-1) resistant to tamoxifen to investigate this mechanism. We demonstrate that TamR-1 express elevated levels of phosphorylated AKT and MAPK3/1-activated RPS6KA2 compared with the parental MCF-7 cell line (MCF-7). There was no change in the level of total ESR between the two cell lines; however, the TamR-1 cells had increased phosphorylation of ESR1 ser167. SiRNA blockade of AKT or MAPK3/1 had little effect on ESR1 ser167 phosphorylation, but a combination of the two siRNAs abrogated this. Co-localization studies revealed an association between ERBB2 and ESR1 in the TamR-1 but not MCF-7 cells. ESR1 was redistributed to extranuclear sites in TamR-1 and was less transcriptionally competent compared with MCF-7 suggesting that nuclear ESR1 activity was suppressed in TamR-1. Tamoxifen resistance in the TamR-1 cells could be partially overcome by the ERBB2 inhibitor AG825 in combination with tamoxifen, and this was associated with re-localization of ESR1 to the nucleus. These data demonstrate that tamoxifen-resistant cells have the ability to switch between ERBB2 or ESR1 pathways promoting cell growth and that pharmacological inhibition of ERBB2 may be a therapeutic strategy for overcoming tamoxifen resistance.
Richard J Santen, Norman F Boyd, Rowan T Chlebowski, Steven Cummings, Jack Cuzick, Mitch Dowsett, Douglas Easton, John F Forbes, Tim Key, Susan E Hankinson, Anthony Howell and James Ingle
The majority of candidates for breast cancer prevention have not accepted tamoxifen because of the perception of an unfavorable risk/benefit ratio and the acceptance of raloxifene remains to be determined. One means of improving this ratio is to identify women at very high risk of breast cancer. Family history, age, atypia in a benign biopsy, and reproductive factors are the main parameters currently used to determine risk. The most powerful risk factor, mammographic density, is not presently employed routinely. Other potentially important factors are plasma estrogen and androgen levels, bone density, weight gain, age of menopause, and fracture history, which are also not currently used in a comprehensive risk prediction model because of lack of prospective validation. The Breast Cancer Prevention Collaborative Group (BCPCG) met to critically examine and prioritize risk factors that might be selected for further testing by multivariate analysis using existing clinical material. The BCPCG reached a consensus that quantitative breast density, state of the art plasma estrogen and androgen measurements, history of fracture and height loss, BMI, and waist–hip ratio had sufficient priority for further testing. As a practical approach, these parameters could be added to the existing Tyrer–Cuzick model which encompasses factors included in both the Claus and Gail models. The BCPCG analyzed potentially available clinical material from previous prospective studies and determined that a large case/control study to evaluate these new factors might be feasible at this time.
Deborah J Thompson, Tracy A O'Mara, Dylan M Glubb, Jodie N Painter, Timothy Cheng, Elizabeth Folkerd, Deborah Doody, Joe Dennis, Penelope M Webb, for the Australian National Endometrial Cancer Study Group (ANECS), Maggie Gorman, Lynn Martin, Shirley Hodgson, for the National Study of Endometrial Cancer Genetics Group (NSECG), Kyriaki Michailidou, Jonathan P Tyrer, Mel J Maranian, Per Hall, Kamila Czene, Hatef Darabi, Jingmei Li, Peter A Fasching, Alexander Hein, Matthias W Beckmann, Arif B Ekici, Thilo Dörk, Peter Hillemanns, Matthias Dürst, Ingo Runnebaum, Hui Zhao, Jeroen Depreeuw, Stefanie Schrauwen, Frederic Amant, Ellen L Goode, Brooke L Fridley, Sean C Dowdy, Stacey J Winham, Helga B Salvesen, Jone Trovik, Tormund S Njolstad, Henrica M J Werner, Katie Ashton, Tony Proietto, Geoffrey Otton, Luis Carvajal-Carmona, Emma Tham, Tao Liu, Miriam Mints, for RENDOCAS, Rodney J Scott, Mark McEvoy, John Attia, Elizabeth G Holliday, Grant W Montgomery, Nicholas G Martin, Dale R Nyholt, Anjali K Henders, John L Hopper, Nadia Traficante, for the AOCS Group, Matthias Ruebner, Anthony J Swerdlow, Barbara Burwinkel, Hermann Brenner, Alfons Meindl, Hiltrud Brauch, Annika Lindblom, Diether Lambrechts, Jenny Chang-Claude, Fergus J Couch, Graham G Giles, Vessela N Kristensen, Angela Cox, Manjeet K Bolla, Qin Wang, Stig E Bojesen, Mitul Shah, Robert Luben, Kay-Tee Khaw, Paul D P Pharoah, Alison M Dunning, Ian Tomlinson, Mitch Dowsett, Douglas F Easton and Amanda B Spurdle
Candidate gene studies have reported CYP19A1 variants to be associated with endometrial cancer and with estradiol (E2) concentrations. We analyzed 2937 single nucleotide polymorphisms (SNPs) in 6608 endometrial cancer cases and 37 925 controls and report the first genome wide-significant association between endometrial cancer and a CYP19A1 SNP (rs727479 in intron 2, P=4.8×10−11). SNP rs727479 was also among those most strongly associated with circulating E2 concentrations in 2767 post-menopausal controls (P=7.4×10−8). The observed endometrial cancer odds ratio per rs727479 A-allele (1.15, CI=1.11–1.21) is compatible with that predicted by the observed effect on E2 concentrations (1.09, CI=1.03–1.21), consistent with the hypothesis that endometrial cancer risk is driven by E2. From 28 candidate-causal SNPs, 12 co-located with three putative gene-regulatory elements and their risk alleles associated with higher CYP19A1 expression in bioinformatical analyses. For both phenotypes, the associations with rs727479 were stronger among women with a higher BMI (Pinteraction=0.034 and 0.066 respectively), suggesting a biologically plausible gene-environment interaction.