DES Research Heats Up Again After Breast Cancer Finding

Journal of the National Cancer Institute, August 1999

“Based on continued cohort studies, we are now fairly sure that DES women face a 20% to 30% excess risk for breast cancer,”

Robert Hoover, M.D., director of the Epidemiology and Biostatistics Program at the National Cancer Institute

“DES could serve the study of other potential estrogenic cancer-causing compounds and environmental estrogens — none are as potent as DES and it would make an excellent model,”

Retha Newbold, head of the Developmental Endocrinology Section at the National Institute of Environmental Health Sciences, Research Triangle Park, N.C.

Another recommendation from the group was that researchers start to examine grandchildren of DES-exposed women, as they too may have a potential for DES cancers.

Read the full paper DES Research Heats Up Again After Breast Cancer Finding on Oxford University Press, 18 August 1999.


Maternal factors and breast cancer risk among young women

Intrauterine DES exposure and subsequent risk of breast cancer

1998 Study Abstract

The results from previous studies have provided evidence to support the hypothesised association between intrauterine oestrogen exposure and subsequent risk of breast cancer. Information has not been available to study this relationship for several perinatal factors thought to be related to pregnancy oestrogen levels.

Data collected from the mothers of women in two population-based case-control studies of breast cancer in women under the age of 45 years (510 case mothers, 436 control mothers) who were diagnosed between 1983 and 1992 in three western Washington counties were used to investigate further the relationship between intrauterine oestrogen exposure and risk of breast cancer.

A pregnancy weight gain of 25-34 pounds was associated with breast cancer risk (odds ratio [OR] = 1.5; 95% confidence interval [CI] 1.1, 2.0); however, women whose mothers gained 35 pounds or more were not at increased risk. Use of antiemetic medication in women with any nausea and vomiting (OR = 2.9; 95% CI 1.1, 8.1) and use of diethylstilboestrol (DES) (OR = 2.3; 95% CI 0.8, 6.4) appeared to be positively associated with breast cancer risk.

The results from this study provide limited support for the hypothesis that in utero oestrogen exposure may be related to subsequent breast cancer risk among young women.


  • Maternal factors and breast cancer risk among young women, Paediatric and perinatal epidemiology, NCBI PubMed PMID: 9805713, 1998 Oct.
  • Image credit Asdrubal luna.

Prenatal and perinatal risk factors for breast cancer in young women

There is increasing interest in the role of early life exposures in breast carcinogenesis, especially estrogen exposure in utero

1997 Study Abstract

Estrogen levels during pregnancy may be higher in twin pregnancies and among older women and slightly lower among smokers.

We analyzed early life risk factors in a population-based case-control study in the United States of 2,202 breast cancer cases and 2,009 controls under age 55 years. Twins were at an increased risk of breast cancer compared with singletons (relative risk = 1.62; 95% confidence interval = 1.0-2.7), particularly women with a twin brother (relative risk = 2.06), a finding consistent with the observation of high estrogen levels in dizygotic twin pregnancies. Little association was seen between maternal age at birth and breast cancer risk.

We carried out further analyses for 534 cases and 497 controls under age 45 years, using data from a questionnaire completed by their mothers relating to the daughters’ early life exposures. There was no evidence of an effect of smoking or diethylstilbestrol exposure during pregnancy on daughters’ breast cancer risk. A reduced breast cancer risk was seen among women who had been breastfed (relative risk = 0.74; 95% confidence interval = 0.6-1.0).

These findings indicate some effect of early life exposures on breast cancer risk, although the role of estrogen exposure may be less central than previously suggested.


  • Prenatal and perinatal risk factors for breast cancer in young women, Epidemiology, NCBI PubMed PMID: 9229211, 1997 Mar.
  • Featured image Jakob.

Premenopausal breast cancer after in-utero exposure to stilboestrol

Breast cancer cases reported in premenopausal DES Daughters

1996 Study Abstract

Two premenopausal women recently presented to the British Columbia Cancer Agency with a history of intrauterine exposure to stilboestrol (diethylstilboestrol, DES) and newly diagnosed breast cancer.

  1. The first, age 28, had known DES sequelae with a bicornate uterus and presented with stage IV breast cancer.
  2. The second, age 34, presented with stage II breast cancer and no previous health problems.

Neither patient had any known familial history of breast cancer, or any other risk factors.



Breast cancer epidemiology : summary and future directions

Epidemiologic reviews, 1993


The most common cancer in US women and the 2nd leading cause of cancer death is breast cancer.

Between 1980-1987 in the US. age-adjusted incidence rates of breast cancer rose rapidly. They are also rising rapidly in several Asian countries (e.g., in Japan) which have the lowest incidence rates. These rapid increases may mean that environmental factors are responsible.

Incidence rates rise greatly with age until the late 40s. US women at highest risk of breast cancer are Jewish women, urban women, single women, and women living in the northern US. Women at lowest risk include Mormon and Seventh-Day Adventist women, Hispanic and Asian women, rural women, women living in the southern US, and married women.

Factors that have a relative risk greater than 2 are

  • mother and sister with history of breast cancer, especially if diagnoses at an early age;
  • atypical epithelial cells in nipple aspirate fluid;
  • nodular densities on the mammogram;
  • history of cancer in 1 breast;
  • mother or sister with history of breast cancer;
  • biopsy-confirmed benign proliferative breast disease;
  • hyperplastic epithelial cells without atypia in nipple aspirate fluid;
  • and radiation to chest in moderate to high doses.

Ovarian hormones appear to stimulate cell division in the breast, thus elevated levels may be risk factors.

Exogenous hormones may also increase the risk. Women are exposed to these exogenous hormones through

  • estrogen replacement therapy,
  • progestin only pills,
  • oral contraceptives,
  • long-acting injectable contraceptives,
  • and diethylstilbestrol.

Postmenopausal obesity increases the risk while premenopausal obesity decreases the risk. A high fat diet in childhood and adolescence may increase the risk. Alcohol drinking may also increase the risk.

Older, white, and nulliparous women are more likely to have estrogen receptor-positive cancers.

Breast cancer in males tends to share the same risk factors as well as its own unique factors.

Prevention of postmenopausal obesity is the only established primary prevention effort. Screening is the only secondary prevention means.



Breast Cancer in DES Daughters

The incidence of breast cancer associated with DES may increase with additional follow-up time

1993 Review Abstract

It is estimated that 2 million US women used diethylstilbestrol (DES), a nonsteroidal estrogen, to reduce the risk of fetal loss from the late 1940s through the early 1960s. The results of clinical trials of the effectiveness of DES in the early 1950s precipitated the eventual decline of DES prescription by the 1960s.

Concern about the breast cancer risk associated with the high dose of stilbestrol used led to 2 follow-up studies of these clinical trial participants, as well as 2 other retrospective cohort studies to examine the subsequent risk of breast cancer in DES-exposed women.

3 of the 4 studies reported positive results, with an overall 50% increase in risk for ever using DES during pregnancy and an apparent latency period of more than 20 years.

These studies have or more limitations, including the absence of information on dosage taken and duration of use, confusion about the identify of the exposed group and the inability to distinguish between the effect of DES and the effect of indications for using DES. Nevertheless, the findings supported a possible association between DES and breast cancer risk.

The 4 studies were published between 1980 and 1984 and included many women who had only recently entered the age period when breast cancer incidence is high. It is possible that the incidence of breast cancer associated with DES may increase with additional follow-up time.

Prenatal influences on carcinogenesis have recently become of interest in the etiology of adult cancer, and, in particular, it has been proposed that increased estrogen levels during pregnancy might increase the probability of breast cancer in daughters. It has been demonstrated that DES use during pregnancy can influence the subsequent risk of clear cell adenocarcinoma in offspring, although the issue of whether DES might also influence the subsequent risk of breast cancer in daughters remains to be investigated.


  • Diethylstilbestrol (DES) and breast cancer, Epidemiologic reviews, NCBI PubMed PMID: 8405194, 1993.

Does breast cancer originate in utero?

Higher risk of breast cancer in women prenatally exposed to diethylstilbestrol

1990 Study Abstract

Factors that increase the risk of cancer during adult life may also increase the risk of cancer when they act in utero (eg, ionising radiation and diethylstilboestrol in human beings and chemicals in animals).

The existing empirical data seem to be compatible with the hypothesis that increased concentrations of oestrogens in pregnancy increase the probability of future occurrence of breast cancer in daughters.


  • Hypothesis: does breast cancer originate in utero?, The Lancet, NCBI PubMed PMID: 1970028, 1990 Apr.
  • Featured image pexels.

DES Exposure Mechanism leading to Breast Cancer

Bisphenol-A and diethylstilbestrol exposure induces the expression of breast cancer associated long noncoding RNA HOTAIR in vitro and in vivo

2014 Study Abstract

Antisense transcript, long non-coding RNA HOTAIR is a key player in gene silencing and breast cancer and is transcriptionally regulated by estradiol. Here, we have investigated if HOTAIR expression is misregulated by bisphenol-A (BPA) and diethylstilbestrol (DES). Our findings demonstrate BPA and DES induce HOTAIR expression in cultured human breast cancer cells (MCF7) as well as in vivo in the mammary glands of rat. Luciferase assay showed that HOTAIR promoter estrogen-response-elements (EREs) are induced by BPA and DES. Estrogen-receptors (ERs) and ER-coregulators such as MLL-histone methylases (MLL1 and MLL3) bind to the HOTAIR promoter EREs in the presence of BPA and DES, modify chromatin (histone methylation and acetylation) and lead to gene activation. Knockdown of ERs down-regulated the BPA and DES induced expression of HOTAIR. In summary, our results demonstrate that BPA and DES exposure alters the epigenetic programming of the HOTAIR promoters leading to its endocrine disruption in vitro and in vivo.

It is important to note that, HOTAIR is an antisense transcript and lncRNA. Therefore, our studies also demonstrate that endocrine disruptors can disrupt the noncoding RNAs and can induce antisense transcripts, in a similar fashion as protein coding genes from the sense strands. Our studies revealed novel epigenetic mechanism of endocrine disruption, novel roles of MLL histone methylases and their coordination with ERs and various ER-coregulators during endocrine disruption, both in vitro and in vivo. Although further in vivo analyses are required to understand the detailed mechanism of HOTAIR gene expression and misregulation by EDCs, synthetics estrogens, and other environmental toxins/chemical, our observations indicate that exposure to BPA or DES may turn on the expression of HOTAIR in vivo, in a very similar fashion to estrogen even in the absence of estrogen, and that may result in adverse health effects including cancer and other hormonally regulated disorders.


  • Full study (free access) : Bisphenol-A and diethylstilbestrol exposure induces the expression of breast cancer associated long noncoding RNA HOTAIR in vitro and in vivo, The Journal of steroid biochemistry and molecular biology, NCBI PubMed PMC4025971, 2014.
  • Featured image : Models showing the roles of ERs, MLLs and other ER-coregulators during BPA and DES mediated endocrine disruption of HOTAIR. PMC4025971/figure/F7.

Increased Breast Cancer risk in DES-Exposed Progeny

Maternal exposure to diethylstilbestrol during pregnancy and increased breast cancer risk in daughters, 2014

Study Summary

The idea that susceptibility to breast cancer is determined not only through inherited germline mutations but also by epigenetic changes induced by alterations in hormonal environment during fetal development is gaining increasing support. Using findings obtained in human and animal studies, this review addresses the mechanisms that may explain why daughters of mothers who took synthetic estrogen diethylstilbestrol (DES) during pregnancy have two times higher breast cancer risk than women who were not exposed to it. The mechanisms likely involve epigenetic alterations, such as increased DNA methylation and modifications in histones and microRNA expression.Further, these alterations may target genes that regulate stem cells and prevent differentiation of their daughter cells. Recent findings in a preclinical model suggest that not only are women exposed to DES in utero at an increased risk of developing breast cancer, but this risk may extend to their daughters and granddaughters as well. It is critical, therefore, to determine if the increased risk is driven by epigenetic alterations in genes that increase susceptibility to breast cancer and if these alterations are reversible.


In this review, findings related to in utero DES exposure and breast cancer are discussed for the purpose of weighing evidence as to whether fetal hormonal environment can impact breast cancer risk in women several decades later. Since causal studies can readily be performed using animal models, findings obtained in DES-exposed mouse and rat offspring also are discussed. Importantly, animal studies were done prior to any epidemiological studies addressing a possible link between maternal DES exposure and breast cancer risk among daughters could be performed. By the 1980s, exposed daughters in the cohorts began to be old enough to develop breast cancer and several human studies have been performed since to determine if maternal exposure to DES during pregnancy increases an offspring’s breast cancer risk.

…”The animal studies show that the doses of DES relevant to pregnant women increased later risk of developing mammary tumors. Specifically, female offspring of rat dams exposed to a total of 1.2 μg DES either on gestation week 2 or 3, to 0.6 μg or 4 μg DES on both gestation days 15 and 18 (all via injection), or via diet to 0.1, 1 or 10 ppm DES between gestation days 13 and 21 (week 3) exhibited increased mammary cancer risk. An increase in risk also was seen in rats exposed to a single dose of 0.1, 1 or 10 μg or less of DES at birth.” …

…”Importantly, in utero exposure to DES leads to an increase in terminal end buds (TEBs) numbers. It is thus possible that one of the mechanisms causing an increase in mammary cancer risk in DES offspring is an increase in the number of targets for malignant transformation.”…

…”Several published studies have investigated breast cancer risk in the daughters of DES mothers, the majority of which were cohort studies done in the US. As the women in the cohorts aged, their breast cancer risk grew higher, compared with matched non-exposed controls. The findings clearly indicate that after age 40 years the incidence of breast cancer is at least two-fold higher in the daughters of DES-exposed mothers. Many pregnant women in Europe and Australia also used DES, but the peak exposure occurred 10 to 20 years later than in the US, and this probably explains why a recent study done in Europe found a trend but not a significant increase in breast cancer risk among them. Once the European daughters reach the age when breast cancer is more commonly detected, they too are likely to exhibit a significant increase in breast cancer risk.”…

To summarize, animal and human studies have generated similar findings and indicate that there is a causal link between maternal exposure to DES during pregnancy and increased breast cancer risk among female offspring. According to animal studies, the increase in risk may reflect the presence of a higher number of TEBs in the mammary epithelium in the DES offspring. Baik and colleagues have proposed that the increase in mammary epithelial cells in in utero estrogen-exposed females is caused by a high number of mammary stem cells or an increase in their potential to generate daughter cells. Our unpublished data support this conclusion”

Epigenetic alterations induced by in utero diethylstilbestrol exposure

We and others have observed that the expression of DNA methyltransferases (DNMTs) is persistently altered in estrogen-regulated tissues following estrogenic exposures during early life. In utero exposure to DES is reported to increase the expression of DNMT1 in the epididymis and uterus. We found that DNMT1 expression is increased in the mammary glands of adult rat offspring of dams exposed to ethinyl estradiol during pregnancy. These changes provide a key regulatory layer to influence gene expression in the mammary gland and perhaps breast tumors of individuals exposed to DES or other estrogenic compounds in utero.

The effects of maternal diethylstilbestrol exposure are not limited to the F1 generation?

Some researchers have begun to investigate whether the effects of maternal DES exposure during pregnancy extend to the third generation in humans. Although there is no evidence that DES granddaughters have cervical and ovarian abnormalities similar to DES daughters, there is evidence that they may have more menstrual irregularities and a higher rate of infertility than non-exposed granddaughters. In addition, DES granddaughters may have a slightly higher risk of ovarian cancer. The granddaughters are still too young to assess whether they might also be at an increased risk of developing breast cancer.

Millions of women in the US, Europe and Australia have been exposed to DES in the womb, and consequently exhibit about a two times higher breast cancer risk than unexposed women. The increase in risk may not be limited to the DES-exposed daughters, but could also increase breast cancer risk in granddaughters and great granddaughters. Such outcome would be consistent with the findings we obtained in studies using a synthetic estrogen ethinyl estradiol (EE2). If DES has similar effects to ethinyl estradiol on the transgenerational increase in breast cancer risk, it is urgent to find ways to stop the cycle of inheritance, and also prevent breast cancer in DES-exposed granddaughters and great granddaughters.

To achieve this goal, we need to understand how maternal DES exposure during pregnancy increases a daughter’s breast cancer risk. A plausible model is proposed in the featured image. It is evident from studies done in animal models that in utero DES exposure induces epigenetic changes in reproductive tract tissues and the breast. DES exposure might also have induced epigenetic changes in primordial germ cells and consequently germ cells, and further be detectable in the somatic cells in granddaughters and great granddaughters. We are not aware of any study that has compared epigenetic changes in germ cells and the next generation somatic cells in individuals exposed to DES or other endocrine disruptors in utero. Second, we should investigate whether the transgenerational increase in breast cancer risk can be prevented with drugs that reverse epigenetic modifications. Our preliminary studies in mice suggest that this is achievable in daughters by using the well-tolerated and non-toxic histone deacetylase inhibitor valproic acid and DNMT inhibitor hydralazine. However, whether these compounds also prevent an increase in granddaughters and great granddaughters in experimental models remains to be investigated.


  • Full study (free access) : Maternal exposure to diethylstilbestrol during pregnancy and increased breast cancer risk in daughters, Breast cancer research : BCR, NCBI PubMed PMC4053091, 2014.
  • Featured image : Proposed model to explain an increase in breast cancer risk in daughters, and possibly granddaughters and great granddaughters, of mothers who took diethylstilbestrol during pregnancy. DES, diethylstilbestrol; TDLU, terminal ductal lobular unit; TEB, terminal end bud. PMC4053091/figure/F1.

DES Daughters’ Cancer Risk

Cancer risk in women prenatally exposed to diethylstilbestrol, 2007

Study Abstract

Prenatal diethylstilbestrol (DES) exposure is associated with excess risks of clear cell adenocarcinoma (CCA), and breast cancer in older women. Whether overall cancer risk is also elevated is unclear.

Total and site-specific cancer risks were evaluated in the DES Combined Cohort Follow-up Study using age- and calendar-year specific standardized incidence rate ratios (SIR), and age-adjusted incidence rate ratios (RR) comparing DES exposed and unexposed women. A total of 143 and 49 cancer cases occurred in 97,831 and 34,810 person-years among the exposed and unexposed, respectively.

  • There was no overall excess risk among exposed women when compared with external rates (SIR 1.01; 95% confidence interval [CI] 0.86-1.2).
  • The overall RR comparing exposed with unexposed women was 1.32 (95% CI 0.94-1.8).
  • Breast cancer risk was elevated only among women over 40 years (RR 1.83; 95% CI 1.1-3.2).
  • The CCA SIR among exposed women was nearly 40, and the estimated attack rate through age 39 was 1.6/1,000 women. CCA incidence decreased by over 80% after age 25 when compared with 20-24 years.
  • Excluding CCA and breast cancer, the overall RR was 1.21 (95% CI 0.74-2.0).
  • DES was not associated with excess risks of either endometrial or ovarian cancer.

These data suggest that the DES associated increase in CCA incidence remains elevated through the reproductive years. There was no consistent evidence of risk excesses for cancers other than CCA, and breast cancer in older women.

Given that the population is still young, continued follow-up is necessary to assess the overall carcinogenic impact of prenatal DES exposure.


  • Cancer risk in women prenatally exposed to diethylstilbestrol, International journal of cancer, NCBI PubMed PMID: 17390375, 2007 Jul 15.