Breast development, also known as mammogenesis, is a complex biological process in primates that takes place throughout a female's life.
It occurs across several phases, including prenatal development, puberty, and pregnancy. At menopause, breast development ceases and the breasts atrophy. Breast development results in prominent and developed structures on the chest known as breasts in primates, which serve primarily as mammary glands. The process is mediated by an assortment of hormones (and growth factors), the most important of which include estrogen, progesterone, prolactin, and growth hormone.
The master regulators of breast development are the steroid hormones, estrogen, and progesterone, growth hormone (GH), mostly via its secretory product, insulin-like growth factor 1 (IGF-1), and prolactin. [1] These regulators induce the expression of growth factors, such as amphiregulin, epidermal growth factor (EGF), IGF-1, and fibroblast growth factor (FGF), which in turn have specific roles in breast growth and maturation. [1]
At puberty, gonadotropin-releasing hormone (GnRH) is secreted in a pulsatile manner from the hypothalamus. [2] [3] GnRH induces the secretion of the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), from the pituitary gland. [2] [3] The secreted gonadotropins travel through the bloodstream to the ovaries and trigger the secretion of estrogen and progesterone in fluctuating amounts during each menstrual cycle. [2] [3] Growth hormone (GH), which is secreted from the pituitary gland, and insulin-like growth factor 1 (IGF-1), which is produced in the body in response to GH, are growth-mediating hormones. [4] During prenatal development, infancy, and childhood, GH and IGF-1 levels are low, but progressively increase and reach a peak at puberty, [5] with a 1.5- to 3-fold increase in pulsatile GH secretion and a 3-fold or greater increase in serum IGF-1 levels being capable of occurring at this time. [6] In late adolescence and early adulthood, GH and IGF-1 levels significantly decrease, [7] and continue to decrease throughout the rest of life. [5] It has been found that both estrogen and GH are essential for breast development at puberty – in the absence of either, no development will take place. [8] [9] Moreover, most of the role of GH in breast development has been found to be mediated by its induction of IGF-1 production and secretion, as IGF-1 administration rescues breast development in the absence of GH. [9] GH induction of IGF-1 production and secretion occurs in almost all types of tissue in the body, but especially in the liver, which is the source of approximately 80% of circulating IGF-1, [10] as well as locally in the breasts. [5] [11] Although IGF-1 is responsible for most of the role of GH in mediating breast development, GH itself has been found to play a direct, augmenting role as well, as it increases estrogen receptor (ER) expression in breast stromal (connective) tissue, while IGF-1, in contrast, has been found to not do this. [12] [13] In addition to estrogen and GH/IGF-1 both being essential for pubertal breast development, they are synergistic in bringing it about. [8] [9] [14]
Despite the apparent necessity of GH/IGF-1 signaling in pubertal breast development however, women with Laron syndrome, in whom the growth hormone receptor (GHR) is defective and insensitive to GH and serum IGF-1 levels are very low, puberty, including breast development, is delayed, although full sexual maturity is always eventually reached. [15] Moreover, breast development and size are normal (albeit delayed) in spite of GH/IGF-1 axis insufficiency, and in some the breasts may actually be large in relation to body size. [15] [16] The relatively large breasts in women with Laron syndrome have been suggested to be due to increased secretion of prolactin (which is known to produce breast enlargement) caused by a drift phenomenon from somatomammotrophic cells in the pituitary gland with a high GH secretion. [15] [16] An animal model of Laron syndrome, the GHR knockout mouse, shows severely impaired ductal outgrowth at 11 weeks of age. [17] [18] [19] However, by 15 weeks, ductal development has caught up with that of normal mice and the ducts have fully distributed throughout the mammary fat pad, although the ducts remain narrower than those of wild-type mice. [17] [18] [19] In any case, female GHR knockout mice can lactate normally. [17] [19] As such, it has been said that the phenotypes of women with Laron syndrome and GHR knockout mice are identical, with diminished body size and delayed sexual maturation accompanied by normal lactation. [17] These data indicate that very low circulating levels of IGF-1 can nonetheless allow for full pubertal breast development. [15] [17]
Development of the breasts during the prenatal stage of life is independent of biological sex and sex hormones. [20] During embryonic development, the breast buds, in which networks of tubules are formed, are generated from the ectoderm. [21] These rudimentary tubules will eventually become the matured lactiferous (milk) ducts, which connect the lobules (milk "containers") of the breast, grape-like clusters of alveoli, to the nipples. [22] Until puberty, the tubule networks of the breast buds remain rudimentary and quiescent, [1] and the male and female breast do not show any differences. [20] During puberty in females, estrogen, in conjunction with GH/IGF-1, through activation of ERα specifically (and notably not ERβ or GPER), [23] [24] causes growth of and transformation of the tubules into the matured ductal system of the breasts. [20] [21] [25] Under the influence of estrogen, the ducts sprout and elongate, and terminal end buds (TEBs), bulbous structures at the tips of the ducts, penetrate into the fat pad and branch as the ducts elongate. [20] [21] [25] This continues until a tree-like network of branched ducts that is embedded into and fills the entire fat pad of the breast is formed. [1] [20] [21] [25] In addition to its role in mediating ductal development, estrogen causes stromal tissue to grow and adipose (fat) tissue to accumulate, [20] [21] as well as the nipple-areolar complex to increase in size. [26]
Progesterone, in conjunction with GH/IGF-1 similarly to estrogen, affects the development of the breasts during puberty and thereafter as well. [20] [21] [25] To a lesser extent than estrogen, progesterone contributes to ductal development at this time, as evidenced by the findings that progesterone receptor (PR) knockout mice or mice treated with the PR antagonist mifepristone show delayed (albeit eventually normal, due to estrogen acting on its own) ductal growth during puberty and by the fact that progesterone has been found to induce ductal growth on its own in the mouse mammary gland mainly via the induction of the expression of amphiregulin, the same growth factor that estrogen primarily induces to mediate its actions on ductal development. [27] In addition, progesterone produces modest lobuloalveolar development (alveolar bud formation or ductal sidebranching) starting at puberty, [20] [25] specifically through activation of PRB (and notably not PRA), [28] with growth and regression of the alveoli occurring to some degree with each menstrual cycle. [20] [21] However, only rudimentary alveoli develop in response to pre-pregnancy levels of progesterone and estrogen, and lobuloalveolar development will remain at this stage until pregnancy occurs, if it does. [21] In addition to GH/IGF-1, estrogen is required for progesterone to affect the breasts, [20] [25] as estrogen primes the breasts by inducing the expression of the progesterone receptor (PR) in breast epithelial tissue. [28] In contrast to the case of the PR, ER expression in the breast is stable and differs relatively little in the contexts of reproductive status, stage of the menstrual cycle, or exogenous hormonal therapy. [28]
During pregnancy, pronounced breast growth and maturation occurs in preparation of lactation and breastfeeding. [20] [29] [30] Estrogen and progesterone levels increase dramatically, [20] reaching levels by late pregnancy that are several hundred-fold higher than usual menstrual cycle levels. [31] Estrogen and progesterone cause the secretion of high levels of prolactin from the anterior pituitary, [32] [33] which reach levels as high as 20 times greater than normal menstrual cycle levels. [31] IGF-1 and IGF-2 levels also increase dramatically during pregnancy, due to secretion of placental growth hormone (PGH). [34] Further ductal development, by estrogen, again in conjunction with GH/IGF-1, occurs during pregnancy. [21] [22] In addition, the concert of estrogen, progesterone (again specifically through PRB), [28] prolactin, and other lactogens such as human placental lactogen (hPL) and PGH, in conjunction with GH/IGF-1, as well as insulin-like growth factor 2 (IGF-2), [35] [36] acting together, mediate the completion of lobuloalveolar development of the breasts during pregnancy. [21] [22] [37] [38] Both PR and prolactin receptor (PRLR) knockout mice fail to show lobuloalveolar development, and progesterone and prolactin have been found to be synergistic in mediating growth of alveoli, demonstrating the essential role of both of these hormones in this aspect of breast development. [39] [40] Growth hormone receptor (GHR) knockout mice also show greatly impaired lobuloalveolar development. [41] In addition to their role in lobuloalveolar growth, prolactin and hPL act to increase the size of the nipple-areolar complex during pregnancy. [42] By the end of the fourth month of pregnancy, at which time lobuloalveolar maturation is complete, the breasts are fully prepared for lactation and breastfeeding. [30]
Insulin, glucocorticoids such as cortisol (and by extension adrenocorticotropic hormone (ACTH)), and thyroid hormones such as thyroxine (and by extension thyroid-stimulating hormone (TSH) and thyrotropin-releasing hormone (TRH)) also play permissive but less well-understood/poorly-characterized roles in breast development during both puberty and pregnancy, and are required for full functional development. [43] [44] [45] [46] Leptin has also been found to be an important factor in mammary gland development, and has been found to promote mammary epithelial cell proliferation. [2] [47]
In contrast to the female-associated sex hormones, estrogen and progesterone, the male-associated sex hormones, the androgens, such as testosterone and dihydrotestosterone (DHT), powerfully suppress the action of estrogen in the breasts. [37] [46] [48] [49] At least one way that they do this is by reducing the expression of the estrogen receptor in breast tissue. [48] [49] [50] In the absence of androgenic activity, such as in women with complete androgen insensitivity syndrome (CAIS), modest levels of estrogen (50 pg/mL) are capable of mediating significant breast development, with CAIS women showing breast volumes that are even above-average. [37] The combination of much higher levels of androgens (about 10-fold higher) and much lower levels of estrogen (about 10-fold less), [51] due to the ovaries in females producing high amounts of estrogens but low amounts of androgens and the testes in males producing high amounts of androgens but low amounts of estrogens, [52] are why males generally do not grow prominent or well-developed breasts relative to females. [46] [53]
Calcitriol, the hormonally active form of vitamin D, acting through the vitamin D receptor (VDR), has, like the androgens, been reported to be a negative regulator of mammary gland development in mice, for instance, during puberty. [41] VDR knockout mice show more extensive ductal development relative to wild-type mice, [54] as well as precocious mammary gland development. [55] In addition, VDR knockout has also been shown to result in increased responsiveness of mouse mammary gland tissue to estrogen and progesterone, which was represented by increased cell growth in response to these hormones. [54] Conversely however, it has been found that VDR knockout mice show reduced ductal differentiation, represented by an increased number of undifferentiated TEBs, [56] and this finding has been interpreted as indicating that vitamin D may be essential for lobuloalveolar development. [40] As such, calcitriol, via the VDR, may be a negative regulator of ductal development but a positive regulator of lobuloalveolar development in the mammary gland. [57]
A possible mechanism of the negative regulatory effects of the VDR on breast development may be indicated by a study of vitamin D3 supplementation in women which found that vitamin D3 suppresses cyclooxygenase-2 (COX-2) expression in the breast, and by doing so, reduces and increases, respectively, the levels of prostaglandin E2 (PGE2) and transforming growth factor β2 (TGF-β2), a known inhibitory factor in breast development. [58] Moreover, suppression of PGE2 in breast tissue is relevant because, via activation of prostaglandin EP receptors, PGE2 potently induces amphiregulin expression in breast tissue, and activation of the EGFR by amphiregulin increases COX-2 expression in breast tissue, in turn resulting in more PGE2, and thus, a self-perpetuating, synergistic cycle of growth amplification due to COX-2 appears to potentially be present in normal breast tissue. [59] [60] Accordingly, overexpression of COX-2 in mammary gland tissue produces mammary gland hyperplasia as well as precocious mammary gland development in female mice, mirroring the phenotype of VDR knockout mice, and demonstrating a strong stimulatory effect of COX-2, which is downregulated by VDR activation, on the growth of the mammary glands. [59] [60] Also in accordance, COX-2 activity in the breasts has been found to be positively associated with breast volume in women. [61]
Estrogen, progesterone, and prolactin, as well as GH/IGF-1, produce their effects on breast development by modulating the local expression in breast tissue of an assortment of autocrine and paracrine growth factors, [25] [44] [62] [63] [64] including IGF-1, IGF-2, amphiregulin, [65] EGF, FGF, hepatocyte growth factor (HGF), [66] tumor necrosis factor α (TNF-α), tumor necrosis factor β (TNF-β), transforming growth factor α (TGF-α), [67] transforming growth factor β (TGF-β), [68] heregulin, [69] Wnt, [40] RANKL, [40] and leukemia inhibitory factor (LIF). [40] These factors regulate cellular growth, proliferation, and differentiation via activation of intracellular signaling cascades that control cell function, such as Erk, Akt, JNK, and Jak/Stat. [10] [70] [71] [72]
Based on research with epidermal growth factor receptor (EGFR) knockout mice, the EGFR, which is the molecular target of EGF, TGF-α, amphiregulin, and heregulin, has, similarly to the insulin-like growth factor-1 receptor (IGF-1R), [1] been found to be essential for mammary gland development. [73] Estrogen and progesterone mediate ductal development mainly through induction of amphiregulin expression, and thus downstream EGFR activation. [27] [65] [70] [74] [75] Accordingly, ERα, amphiregulin, and EGFR knockout mice copy each other phenotypically in regards to their effects on ductal development. [74] Also in accordance, treatment of mice with amphiregulin or other EGFR ligands like TGF-α or heregulin induces ductal and lobuloalveolar development in the mouse mammary gland, actions that occur even in the absence of estrogen and progesterone. [69] [76] As both the IGF-1R and the EGFR are independently essential for mammary gland development, and as combined application of IGF-1 and EGF, through their respective receptors, has been found to synergistically stimulate the growth of human breast epithelial cells, these growth factor systems appear to work together in mediating breast development. [77] [78] [79]
Elevated levels of HGF and, to a lesser extent, IGF-1 (by 5.4-fold and 1.8-fold, respectively), in breast stromal tissue, have been found in macromastia, a very rare condition of extremely and excessively large breast size. [80] Exposure of macromastic breast stromal tissue to non-macromastic breast epithelial tissue was found to cause increased alveolar morphogenesis and epithelial proliferation in the latter. [80] A neutralizing antibody for HGF, but not for IGF-1 or EGF, was found to attenuate the proliferation of breast epithelial tissue caused by exposure to macromastic breast stromal cells, potentially directly implicating HGF in the breast growth and enlargement seen in macromastia. [80] Also, a genome-wide association study has highly implicated HGF and its receptor, c-Met, in breast cancer aggressiveness. [81]
Upon parturition (childbirth), estrogen and progesterone rapidly drop to very low levels, with progesterone levels being undetectable. [20] Conversely, prolactin levels remain elevated. [20] [29] As estrogen and progesterone block prolactin-induced lactogenesis by suppressing prolactin receptor (PRLR) expression in breast tissue, their sudden absence results in the commencement of milk production and lactation by prolactin. [20] [29] Expression of the PRLR in breast tissue may increase by as much as 20-fold when estrogen and progesterone levels drop upon childbirth. [20] With suckling from the infant, prolactin and oxytocin are secreted and mediate milk production and letdown, respectively. [20] [21] [29] Prolactin suppresses the secretion of LH and FSH, which in turn results in continued low levels of estrogen and progesterone, and temporary amenorrhea (absence of menstrual cycles) occurs. [29] In the absence of regular, episodic suckling, which keeps prolactin concentrations high, levels of prolactin will quickly drop, the menstrual cycle will resume and hence normal estrogen and progesterone levels will return, and lactation will cease (that is, until next parturition, or until induced lactation (i.e., with a galactogogue), occurs). [29]
Some factors of breast morphology, including their density, are clearly implicated in breast cancer. While breast size is moderately heritable, the relationship between breast size and cancer is uncertain. The genetic variants influencing breast size have not been identified. [82]
Through genome-wide association studies, a variety of genetic polymorphisms have been linked to breast size. [82] Some of these include rs7816345 near ZNF703 (zinc finger protein 703); rs4849887 and rs17625845 flanking INHBB (inhibin βB); rs12173570 near ESR1 (ERα); rs7089814 in ZNF365 (zinc finger protein 365); rs12371778 near PTHLH (parathyroid hormone-like hormone); rs62314947 near AREG (amphiregulin); [82] as well as rs10086016 at 8p11.23 (which is in complete linkage disequilibrium with rs7816345) and rs5995871 at 22q13 (contains the MKL1 gene, which has been found to modulate the transcriptional activity of ERα). [83] Many of these polymorphisms are also associated with the risk of developing breast cancer, revealing a potential positive association between breast size and breast cancer risk. [82] [83] However, conversely, some polymorphisms show a negative association between breast size and breast cancer risk. [83] In any case, a meta-analysis concluded that breast size and risk of breast cancer are indeed importantly related. [84]
Circulating IGF-1 levels are positively associated with breast volume in women. [85] In addition, the absence of the common 19-repeat allele in the IGF1 gene is also positively associated with breast volume in women, as well as with high IGF-1 levels during oral contraceptive use and with lessening of the normal age-associated decline in circulating IGF-1 concentrations in women. [85] There is great variation in the prevalence of the IGF1 19-repeat allele between ethnic groups, and its absence has been reported to be highest among African-American women. [85]
Genetic variations in the androgen receptor (AR) have been linked to both breast volume (as well as body mass index) and breast cancer aggressiveness. [86]
COX-2 expression has been positively associated with breast volume and inflammation in breast tissue, as well as with breast cancer risk and prognosis. [61]
Women with CAIS, who are completely insensitive to the AR-mediated actions of androgens, have, as a group, above-average sized breasts. This is true despite the fact that they simultaneously have relatively low levels of estrogen, which demonstrates the powerful suppressant effect of androgens on estrogen-mediated breast development. [37]
Aromatase excess syndrome, an extremely rare condition characterized by marked hyperestrogenism, is associated with precocious breast development and macromastia in females and similarly precocious gynecomastia (women's breasts) in males. [87] [88] [89] In complete androgen insensitivity syndrome, a condition in which the AR is defective and insensitive to androgens, there is full breast development with breast volumes that are in fact above average in spite of relatively low levels of estrogen (50 pg/mL estradiol). [37] In aromatase deficiency, a form of hypoestrogenism in which aromatase is defective and cannot synthesize estrogen, and in complete estrogen insensitivity syndrome, a condition in which ERα is defective and insensitive to estrogen, breast development is completely absent. [90] [91] [92]
The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryological tissues.
Estrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal activity: estrone (E1), estradiol (E2), and estriol (E3). Estradiol, an estrane, is the most potent and prevalent. Another estrogen called estetrol (E4) is produced only during pregnancy.
Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the major progestogen in the body. Progesterone has a variety of important functions in the body. It is also a crucial metabolic intermediate in the production of other endogenous steroids, including the sex hormones and the corticosteroids, and plays an important role in brain function as a neurosteroid.
Prolactin (PRL), also known as lactotropin and mammotropin, is a protein best known for its role in enabling mammals to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans. Prolactin is secreted from the pituitary gland in response to eating, mating, estrogen treatment, ovulation and nursing. It is secreted heavily in pulses in between these events. Prolactin plays an essential role in metabolism, regulation of the immune system and pancreatic development.
A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word mamma, "breast". The mammary glands are arranged in organs such as the breasts in primates, the udder in ruminants, and the dugs of other animals. Lactorrhea, the occasional production of milk by the glands, can occur in any mammal, but in most mammals, lactation, the production of enough milk for nursing, occurs only in phenotypic females who have gestated in recent months or years. It is directed by hormonal guidance from sex steroids. In a few mammalian species, male lactation can occur. With humans, male lactation can occur only under specific circumstances.
Insulin-like growth factor 1 (IGF-1), also called somatomedin C, is a hormone similar in molecular structure to insulin which plays an important role in childhood growth, and has anabolic effects in adults.
Mouse mammary tumor virus (MMTV) is a milk-transmitted retrovirus like the HTL viruses, HI viruses, and BLV. It belongs to the genus Betaretrovirus. MMTV was formerly known as Bittner virus, and previously the "milk factor", referring to the extra-chromosomal vertical transmission of murine breast cancer by adoptive nursing, demonstrated in 1936, by John Joseph Bittner while working at the Jackson Laboratory in Bar Harbor, Maine. Bittner established the theory that a cancerous agent, or "milk factor", could be transmitted by cancerous mothers to young mice from a virus in their mother's milk. The majority of mammary tumors in mice are caused by mouse mammary tumor virus.
Steroid hormone receptors are found in the nucleus, cytosol, and also on the plasma membrane of target cells. They are generally intracellular receptors and initiate signal transduction for steroid hormones which lead to changes in gene expression over a time period of hours to days. The best studied steroid hormone receptors are members of the nuclear receptor subfamily 3 (NR3) that include receptors for estrogen and 3-ketosteroids. In addition to nuclear receptors, several G protein-coupled receptors and ion channels act as cell surface receptors for certain steroid hormones.
Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testicles, thyroid gland, parathyroid gland, hypothalamus and adrenal glands. The hypothalamus and pituitary glands are neuroendocrine organs.
The epidermal growth factor receptor is a transmembrane protein that is a receptor for members of the epidermal growth factor family of extracellular protein ligands.
Amphiregulin, also known as AREG, is a protein synthesized as a transmembrane glycoprotein with 252 aminoacids and it is encoded by the AREG gene. in humans.
The progesterone receptor (PR), also known as NR3C3 or nuclear receptor subfamily 3, group C, member 3, is a protein found inside cells. It is activated by the steroid hormone progesterone.
The prolactin receptor (PRLR) is a type I cytokine receptor encoded in humans by the PRLR gene on chromosome 5p13-14. It is the receptor for prolactin (PRL). The PRLR can also bind to and be activated by growth hormone (GH) and human placental lactogen (hPL). The PRLR is expressed in the mammary glands, pituitary gland, and other tissues. It plays an important role in lobuloalveolar development of the mammary glands during pregnancy and in lactation.
The insulin-like growth factor 1 (IGF-1) receptor is a protein found on the surface of human cells. It is a transmembrane receptor that is activated by a hormone called insulin-like growth factor 1 (IGF-1) and by a related hormone called IGF-2. It belongs to the large class of tyrosine kinase receptors. This receptor mediates the effects of IGF-1, which is a polypeptide protein hormone similar in molecular structure to insulin. IGF-1 plays an important role in growth and continues to have anabolic effects in adults – meaning that it can induce hypertrophy of skeletal muscle and other target tissues. Mice lacking the IGF-1 receptor die late in development, and show a dramatic reduction in body mass. This testifies to the strong growth-promoting effect of this receptor.
Insulin-like growth factor-binding protein 3, also known as IGFBP-3, is a protein that in humans is encoded by the IGFBP3 gene. IGFBP-3 is one of six IGF binding proteins that have highly conserved structures and bind the insulin-like growth factors IGF-1 and IGF-2 with high affinity. IGFBP-7, sometimes included in this family, shares neither the conserved structural features nor the high IGF affinity. Instead, IGFBP-7 binds IGF1R, which blocks IGF-1 and IGF-2 binding, resulting in apoptosis.
Feminizing hormone therapy, also known as transfeminine hormone therapy, is hormone therapy and sex reassignment therapy to change the secondary sex characteristics of transgender people from masculine or androgynous to feminine. It is a common type of transgender hormone therapy and is used to treat transgender women and non-binary transfeminine individuals. Some, in particular intersex people, but also some non-transgender people, take this form of therapy according to their personal needs and preferences.
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process naturally occurs with all sexually mature female mammals, although it may predate mammals. The process of feeding milk in all female creatures is called nursing, and in humans it is also called breastfeeding. Newborn infants often produce some milk from their own breast tissue, known colloquially as witch's milk.
Hormonal regulation occurs at every stage of development. A milieu of hormones simultaneously affects development of the fetus during embryogenesis and the mother, including human chorionic gonadotropin (hCG) and progesterone (P4).
Gynecomastia is the abnormal non-cancerous enlargement of one or both breasts in males due to the growth of breast tissue as a result of a hormone imbalance between estrogens and androgens. Gynecomastia can cause significant psychological distress or unease.
Cathrin Brisken is a German and Swiss medical doctor, researcher, and professor at the École Polytechnique Fédérale de Lausanne (EPFL). Her research focuses on the mechanisms of hormonal control in breast cancer development.