Do female sex hormones initiate breast cancer? A review of the evidence

Menopausal status, adipose tissue, and breast cancer risk: impact of estrogen replacement therapy

The seeds of breast cancer are likely sown in the first two or three decades of life. Rapid weight gain and height in infancy predict breast cancer risk in later life. The age at first pregnancy is also a strong predictor for breast cancer; the earlier the first full-term pregnancy, then the lower the risk of breast cancer in later life. It has been postulated that the breast stem cell number may be the factor linking these observations together. Menopause, per se, is associated with an increase in central adiposity, which is reversed by hormone replacement usage. Breast and nonbreast fat both produce estrogens and cytokines that may promote the growth of small breast cancers making them appear earlier. Obesity also is associated with metabolic syndrome, which is a risk factor for breast cancer. The breast cancer stem cells make up only around 1%-2% of the tumor mass and, yet, are the likely driver for much of a breast cancer's behavior. Future research into breast cancer biology, especially into the cancer stem cells is likely to translate into novel methods of treatment and prevention of this common cancer.

Why does oestrogen-only hormone therapy have such a small impact on breast cancer risk? A hypothesis

There seems to be irrefutable evidence that oestrogen is involved in the pathogenesis of breast cancer. The disease mostly affects women and the epidemiology of breast cancer relates to reproductive markers such as pregnancy, age at menarche and age of menopause. Most breast cancers elaborate oestrogen receptors (ER) and in such cases endocrine therapies such as tamoxifen and aromatase-inhibitors (AIs) are effective adjuvant treatments. However, high-quality randomised controlled trials (RCTs) (such as the WHI study) have shown that oestrogen-only hormone therapy (ET) does not increase breast cancer risk at all. This would seem to be a remarkable paradox. There appears to be at least two reasons for this apparent contradiction. First, it has been known for two decades that the breast itself produces oestrogens locally and the microenvironment around a breast cancer is more important that the impact of systemic-oestrogens. Second, breast cancer stem cells (breast CSC) have been identified and it seems likely that these long-lived, multipotential cells are responsible for the genesis of many breast cancers, as well as their malignant behaviour. Breast CSC usually do not contain sex-hormone receptors, but their offspring often elaborate ER and progesterone receptor (PR). Thus, it appears unlikely that oestrogen per se initiates breast cancer, but rather might stimulate an existing tumour.

Neonatal experiences differentially influence mammary gland morphology, estrogen receptor {α} protein levels, and carcinogenesis in BALB/c mice

Prevention of breast cancer can be achieved with a better understanding of the factors contributing to normal breast development. Because the breast develops postnatally, alterations in the development and lifetime activity of the neuroendocrine system may set up an environment that increases cancer risk. The present study examined how two neonatal experiences over the first 3 weeks of life influence normal and malignant mammary gland development in female BALB/c mice. Following puberty, both brief (15 minutes) and prolonged (4 hours) daily maternal separations of newborn mice accelerated mammary gland development relative to nonseparated mice. Despite similar mammary gland morphologies between mice exposed to these two neonatal separation experiences, only mice exposed to prolonged maternal separation bouts showed a higher incidence and faster onset of mammary tumorigenesis following adulthood carcinogen [7,12-dimethylbenz(a)anthracene] administration. Molecular analysis of estrogen receptor α (ERα) and p53, two proteins that have been implicated in breast cancer, revealed that for mice exposed to prolonged neonatal maternal separation bouts, mammary gland ERα protein levels were upregulated in a transcription-independent manner. On the other hand, p53 expression in mammary glands of adult mice was not differentially influenced by neonatal experiences. Our findings show that chronic, moderate psychosocial stress during the neonatal period increases the expression of ERα protein and promotes mammary tumorigenesis in adulthood.

Breast cancer, stem cells and sex hormones. Part 2: the impact of the reproductive years and pregnancy

The primitive breast develops in utero and during infancy breast growth largely parallels the growth of the child. At puberty, the GnRH pulse generator starts up, initially with just 1-2 pulses daily. This results in very small amounts of unopposed estrogen being secreted by the ovary. As the GnRH pulse generator matures, ovarian secretion of estrogen increases. The pubertal breast responds to this increasing estrogen drive. Breast glandular increase in size is mostly due to growth and division of the primary ducts. Eventually, the terminal buds give rise alveolar buds which tend to cluster around a terminal duct. Lobule formation begins in the first 2 years that follow menarche. With the onset of ovulation, breast mitotic activity increases and is usually maximal in the luteal phase. The final stage of breast maturation occurs during the first full-term pregnancy. The breast undergoes marked changes in preparation for breast feeding. There is evidence that breast SC number decreases during that first pregnancy. Also, the remaining SC undergo significant change which seems to render them less likely to undergo malignant change. These alterations to breast SC number and function may explain, at least in part, why early first pregnancy reduces the risk of breast cancer later in life.

Current patient perceptions on the menopause: a South African perspective

OBJECTIVE

To evaluate current patient perspectives on the postmenopausal period in South Africa.

METHODS

The study was conducted in a specialist private practice in Tygerberg, Cape Town, South Africa during 2004. All women with established postmenopausal status, seen over a period of 18 months, received a survey questionnaire by post. Of the 541 questionnaires that were posted, 421 were returned and 410 were used. Women gave written informed consent.

RESULTS

The average age of the women was 60 years, with almost half (49%) greater than 10 years postmenopausal, and 78.5% were using hormonal therapy (HT). Of note is that 42% had been on HT for more than 10 years. The doctor was the most important source of information (87%), the most frequent reason for initiation of, and the second most frequent reason for discontinuation of therapy. The most important advantages of HT given were skeletal protection (85%) and treatment of vasomotor symptoms (70%), while development of breast cancer was given as the most prominent disadvantage (79%).

CONCLUSION

This group of women was well informed regarding current indications and developments concerning HT. Despite their socioeconomic status, the doctor remained the key factor with regard to information and decision-making.

A multicenter, prospective, randomized, double-blind, placebo-controlled study to investigate the efficacy of a continuous-combined hormone therapy preparation containing 1mg estradiol valerate/2mg dienogest on hot flushes in postmenopausal women

OBJECTIVES

To evaluate the effects of an estrogen-reduced, continuous-combined hormone therapy preparation (HT) containing 1mg estradiol valerate (1EV) and 2mg dienogest (2DNG) on the number of moderate and severe hot flushes.

METHODS

This study compared the effects of an oral continuous-combined HT containing 1mg EV and 2mg DNG (1EV/2DNG) with those of placebo. The planned treatment duration was 12 weeks. Data were obtained from 324 postmenopausal women. The primary efficacy variable was the individual relative change of the mean number of moderate and severe hot flushes per week. Weeks 5-12 of treatment were compared with the 2 weeks preceding the treatment phase.

RESULTS

Moderate and severe hot flushes were reduced by 80.8+/-30.9% in the 1EV/2DNG group and by 41.5+/-39.4% in the placebo group. This difference was statistically significant (p<0.0001; Wilcoxon's rank sum test). The incidence of all types of hot flushes (mild+moderate+severe) was reduced by 75.2+/-30.2% under 1EV/2DNG and by 35.3+/-37.0% under placebo. In the subset of non-hysterectomized women, exposure to 1EV/2DNG led to 2.4+/-6.2 days with bleeding in the reference period of 84 days of treatment, versus 0.3+/-1.3 days in the placebo group. The safety profile of 1EV/2DNG was very similar to that of placebo.

CONCLUSIONS

Continuous-combined HT preparation with 1mg EV and 2mg DNG induced a significant reduction of moderate and severe hot flushes compared to placebo (p<0.0001). Thus, this low-estrogen preparation is an effective and safe option for HT.

Addressing the soy and breast cancer relationship: review, commentary, and workshop proceedings

The impact of soyfood intake on breast cancer risk has been investigated extensively. Much of this focus can be attributed to the soybean being a dietary source that is uniquely rich in isoflavones. The chemical structure of isoflavones is similar to that of estrogen, and isoflavones bind to both estrogen receptors (ER alpha and ER beta) (although they preferentially bind to and activate ER beta) and exert estrogen-like effects under some experimental conditions. Isoflavones also possess nonhormonal properties that are associated with the inhibition of cancer cell growth. Thus, there are several possible mechanisms by which soy may reduce the risk of breast cancer. However, the role of isoflavones in breast cancer has become controversial because, in contrast to the possible beneficial effects, some data from in vitro and animal studies suggest that isoflavones, especially genistein, the aglycone of the main soybean isoflavone genistin, may stimulate the growth of estrogen-sensitive tumors. Limited human data directly address the tumor-promoting effects of isoflavones and soy. Because the use of soyfoods and isoflavone supplements is increasing, it is important from a public health perspective to understand the impact of these products on breast cancer risk in women at high risk of the disease and on the survival of breast cancer patients. To this end, a workshop was held in November 2005 to review the existing literature and to make research recommendations. This paper summarizes the workshop findings and recommendations. The primary research recommendation is that the impact of isoflavones on breast tissue needs to be evaluated at the cellular level in women at high risk for breast cancer.