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Jaesung (Peter) Choi, Reena Desai, Yu Zheng, Mu Yao, Qihan Dong, Geoff Watson, David J Handelsman, and Ulla Simanainen

Haploinsufficient inactivating phosphatase and tensin homolog (Pten) mutations cause Cowden syndrome, an autosomal dominant risk genotype for hormone dependent reproductive cancers. As androgen actions mediated via the androgen receptor (AR) supports uterine growth and may modify uterine cancer risk, we hypothesized that a functional AR may increase PTEN inactivation induced uterine cancer. To test the hypothesis, we compared the PTEN knockout (PTENKO) induced uterine pathology in heterozygous PTENKO and combined heterozygous PTEN and complete AR knockout (PTENARKO) female mice. PTENKO induced uterine pathology was significantly reduced by AR inactivation with severe macroscopic uterine pathology present in 21% of PTENARKO vs 46% of PTENKO at a median age of 45 weeks. This could be due to reduced stroma ERα expression in PTENARKO compared to PTENKO uterus, while AR inactivation did not modify PTEN or P-AKT levels. Unexpectedly, while progesterone (P4) is assumed protective in uterine cancers, serum P4 was significantly higher in PTENKO females compared to WT, ARKO, and PTENARKO females consistent with more corpora lutea in PTENKO ovaries. Serum testosterone and ovarian estradiol were similar between all females. Hence, our results demonstrated AR inactivation mediated protection against PTENKO induced uterine pathology and suggests a potential role for antiandrogens in uterine cancer prevention and treatment.

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W P Bocchinfuso and K S Korach

Introduction Estrogen has been thought to be required for the development, differentiation and function of the female reproductive tract (George & Wilson 1988). It promotes the proliferation of the uterine and vaginal epithelium and ovarian follicular development (Canez et al. 1992); the development of the mammary gland, external genitalia, appropriate reproductive sexual behavior, and other secondary sexual characteristics (George & Wilson 1988). In more non-traditional target tissues, estrogen action has been shown to influence bone development, lipid metabolism and cardiovascular function (Auchus & Fuqua 1994, Ciocca & Vargas Roig 1995). The biological actions of estrogens, particularly 17β-estradiol(estradiol), are mediated through the estrogen receptor, which functions as a ligand-inducible transcription factor and is a member of the nuclear receptor superfamily that bind steroids, thyroid hormone, retinoids, prostanoids and vitamin D1 (Tsai & O'Malley 1994). Like other nuclear receptors, the estrogen receptor is composed of distinct functional domains (Fig. 1)
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Neil Portman, Sarah Alexandrou, Emma Carson, Shudong Wang, Elgene Lim, and C Elizabeth Caldon

Three inhibitors of CDK4/6 kinases were recently FDA approved for use in combination with endocrine therapy, and they significantly increase the progression-free survival of patients with advanced estrogen receptor-positive (ER+) breast cancer in the first-line treatment setting. As the new standard of care in some countries, there is the clinical emergence of patients with breast cancer that is both CDK4/6 inhibitor and endocrine therapy resistant. The strategies to combat these cancers with resistance to multiple treatments are not yet defined and represent the next major clinical challenge in ER+ breast cancer. In this review, we discuss how the molecular landscape of endocrine therapy resistance may affect the response to CDK4/6 inhibitors, and how this intersects with biomarkers of intrinsic insensitivity. We identify the handful of pre-clinical models of acquired resistance to CDK4/6 inhibitors and discuss whether the molecular changes in these models are likely to be relevant or modified in the context of endocrine therapy resistance. Finally, we consider the crucial question of how some of these changes are potentially amenable to therapy.

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Fernand Labrie

The discovery of medical castration with GnRH agonists in 1979 rapidly replaced surgical castration and high doses of estrogens for the treatment of prostate cancer. Soon afterwards, it was discovered that androgens were made locally in the prostate from the inactive precursor DHEA of adrenal origin, a mechanism called intracrinology. Taking into account these novel facts, combined androgen blockade (CAB) using a pure antiandrogen combined with castration in order to block the two sources of androgens was first published in 1982. CAB was the first treatment shown in randomized and placebo-controlled trials to prolong life in prostate cancer, even at the metastatic stage. Most importantly, the results recently obtained with the novel pure antiandrogen enzalutamide as well as with abiraterone, an inhibitor of 17α-hydroxylase in castration-resistant prostate cancer, has revitalized the CAB concept. The effects of CAB observed on survival of heavily pretreated patients further demonstrates the importance of the androgens made locally in the prostate and are a strong motivation to apply CAB to efficiently block all sources of androgens earlier at start of treatment and, even better, before metastasis occurs. The future of research in this field thus seems to be centered on the development of more potent blockers of androgens formation and action in order to obtain better results at the metastatic stage and, for the localized stage, reduce the duration of treatment required to achieve complete apoptosis and control of prostate cancer proliferation before it reaches the metastatic or noncurable stage.

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Christy G Woolcott, Yurii B Shvetsov, Frank Z Stanczyk, Lynne R Wilkens, Kami K White, Christian Caberto, Brian E Henderson, Loïc Le Marchand, Laurence N Kolonel, and Marc T Goodman

To add to the existing evidence that comes mostly from White populations, we conducted a nested case–control study to examine the association between sex hormones and breast cancer risk within the Multiethnic Cohort that includes Japanese American, White, Native Hawaiian, African American, and Latina women. Of the postmenopausal women for whom we had a plasma sample, 132 developed breast cancer during follow-up. Two controls per case, matched on study area (Hawaii, Los Angeles), ethnicity/race, birth year, date and time of blood draw and time fasting, were randomly selected from the women who had not developed breast cancer. Levels of estradiol (E2), estrone (E1), androstenedione, dehydroepiandrosterone (DHEA), and testosterone were quantified by RIA after organic extraction and Celite column partition chromatography. E1 sulfate, DHEA sulfate (DHEAS), and sex hormone-binding globulin (SHBG) were quantified by direct immunoassays. Based on conditional logistic regression, the sex hormones were positively associated and SHBG was negatively associated with breast cancer risk. All associations, except those with DHEAS and testosterone showed a significant linear trend. The odds ratio (OR) associated with a doubling of E2 levels was 2.26 (95% confidence interval (CI) 1.58–3.25), and the OR associated with a doubling of testosterone levels was 1.34 (95% CI 0.98–1.82). The associations in Japanese American women, who constituted 54% of our sample, were similar to or nonsignificantly stronger than in the overall group. This study provides the best evidence to date that the association between sex hormones and breast cancer risk is generalizable to an ethnically diverse population.

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A M Lorincz and S Sukumar

Breast cancer continues to be a major health problem for women in the USA and worldwide. There is a need to identify and take steps to alter modifiable breast cancer risks. Conditions of obesity and overweight are risk factors that have reached epidemic proportions. This article reviews the evidence in the literature that test mechanism-based hypotheses which attempt to provide a molecular basis for a causal link between obesity and breast cancer risk, particularly the effects of metabolic syndrome and insulin resistance, peripheral estrogen aromatization in adipose tissue, and direct effect of adipokines. Future areas for study and implications for therapy are discussed.

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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.

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Tracy Proverbs-Singh, Jarett L Feldman, Michael J Morris, Karen A Autio, and Tiffany A Traina

Prostate cancer (PCa) and breast cancer (BCa) share similarities as hormone-sensitive cancers with a wide heterogeneity of both phenotype and biology. The androgen receptor (AR) is a hormone receptor involved in both benign and malignant processes. Targeting androgen synthesis and the AR pathway has been and remains central to PCa therapy. Recently, there has been increased interest in the role of the AR in BCa development and growth, with results indicating AR co-expression with estrogen, progesterone, and human epidermal growth factor receptors, across all intrinsic subtypes of BCa. Targeting the AR axis is an evolving field with novel therapies in development which may ultimately be applicable to both tumor types. In this review, we offer an overview of available agents which target the AR axis in both PCa and BCa and provide insights into the novel drugs in development for targeting this signaling pathway.

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Michael Derwahl and Diana Nicula

Proliferative thyroid diseases are more prevalent in females than in males. Upon the onset of puberty, the incidence of thyroid cancer increases in females only and declines again after menopause. Estrogen is a potent growth factor both for benign and malignant thyroid cells that may explain the sex difference in the prevalence of thyroid nodules and thyroid cancer. It exerts its growth-promoting effect through a classical genomic and a non-genomic pathway, mediated via a membrane-bound estrogen receptor. This receptor is linked to the tyrosine kinase signaling pathways MAPK and PI3K. In papillary thyroid carcinomas, these pathways may be activated either by a chromosomal rearrangement of the tyrosine receptor kinase TRKA, by RET/PTC genes, or by a BRAF mutation and, in addition, in females they may be stimulated by high levels of estrogen. Furthermore, estrogen is involved in the regulation of angiogenesis and metastasis that are critical for the outcome of thyroid cancer. In contrast to other carcinomas, however, detailed knowledge on this regulation is still missing for thyroid cancer.

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Steven M Hill, Victoria P Belancio, Robert T Dauchy, Shulin Xiang, Samantha Brimer, Lulu Mao, Adam Hauch, Peter W Lundberg, Whitney Summers, Lin Yuan, Tripp Frasch, and David E Blask

The present review discusses recent work on melatonin-mediated circadian regulation, the metabolic and molecular signaling mechanisms that are involved in human breast cancer growth, and the associated consequences of circadian disruption by exposure to light at night (LEN). The anti-cancer actions of the circadian melatonin signal in human breast cancer cell lines and xenografts heavily involve MT1 receptor-mediated mechanisms. In estrogen receptor alpha (ERα)-positive human breast cancer, melatonin suppresses ERα mRNA expression and ERα transcriptional activity via the MT1 receptor. Melatonin also regulates the transactivation of other members of the nuclear receptor superfamily, estrogen-metabolizing enzymes, and the expression of core clock and clock-related genes. Furthermore, melatonin also suppresses tumor aerobic metabolism (the Warburg effect) and, subsequently, cell-signaling pathways critical to cell proliferation, cell survival, metastasis, and drug resistance. Melatonin demonstrates both cytostatic and cytotoxic activity in breast cancer cells that appears to be cell type-specific. Melatonin also possesses anti-invasive/anti-metastatic actions that involve multiple pathways, including inhibition of p38 MAPK and repression of epithelial–mesenchymal transition (EMT). Studies have demonstrated that melatonin promotes genomic stability by inhibiting the expression of LINE-1 retrotransposons. Finally, research in animal and human models has indicated that LEN-induced disruption of the circadian nocturnal melatonin signal promotes the growth, metabolism, and signaling of human breast cancer and drives breast tumors to endocrine and chemotherapeutic resistance. These data provide the strongest understanding and support of the mechanisms that underpin the epidemiologic demonstration of elevated breast cancer risk in night-shift workers and other individuals who are increasingly exposed to LEN.