Effect of twinship on incidence of cancer of the testis, breast, and other sites (Sweden)

The intrauterine environment as reflected by birth size and twin and zygosity status influences insulin action and intracellular glucose metabolism in an age- or time-dependent manner

According to the "fetal origins hypothesis," monozygotic (MZ) twins may be more prone to develop various metabolic abnormalities compared with dizygotic (DZ) twins, and twins all together may be more predisposed to metabolic defects compared with singletons. To determine the impact of twin and zygosity status as well as birth size on in vivo measures of glucose metabolism, we examined 123 young (aged 22-31 years) and 103 elderly (aged 57-66 years) MZ and DZ twins and age-matched singleton control subjects. All participants were born at term with available birth records. Peripheral and hepatic insulin action and intracellular glucose partitioning was determined by a euglycemic-hyperinsulinemic clamp using tritiated glucose combined with indirect calorimetry. In elderly subjects, zygosity status influenced nonoxidative glucose metabolism, while twin status per se was associated with elevated hepatic glucose production during both steady-state periods. Birth weight was associated with nonoxidative glucose metabolism in a nongenetic manner within twins and with a high glucose and low lipid oxidation in singletons. In younger subjects, twin status influenced glucose and lipid oxidation rates. We demonstrate a complex age- or time-dependent relationship between independent markers of fetal environment and glucose homeostasis in twins. The documented differential programming effects associated with either low birth weight and twin or zygosity status all represent known defects of glucose homeostasis in type 2 diabetes.

Breast cancer, oestrogens and environmental pollutants: a re-evaluation from a mixture perspective

The continuing rise in breast cancer incidence rates in almost all Western countries cannot be explained entirely in terms of known risk factors of the disease process. Additional determinants need to be examined, among them exposure to environmental pollutants. With the demonstration that elevated levels of endogenous sex hormones and the use of hormones for the relief of menopausal symptoms are associated with the disease, the oestrogen hypothesis of breast cancer has received further empirical support. This has led to heightened concerns about the possible involvement of oestrogen-like pollutants, such as p,p'-Dichlorodiphenyldichloroethane (DDE). Case-control studies assessing whether women with breast cancer have elevated burdens of p,p'-DDE have produced results not suggestive of a link with cancer risks. However, possible effects of p,p'-DDE and other pollutants cannot be seen in isolation from sex hormones also present in serum. In view of the low potency of p,p'-DDE, and its low levels in serum, it seems unlikely that the chemical on its own will add significantly to the action of sex hormones. However, chemical analyses show that numerous pollutants with oestrogen-like effect profiles can be found in human tissues. Thus, the oestrogen hypothesis of breast cancer should be extended to encompass the multitude of these agents. Viewed from such a perspective, a putative role of organochlorines and other agents in breast cancer should not be dismissed prematurely. Instead, breast cancer epidemiology should face the reality of combined exposures and should take account of recent evidence from in vitro models demonstrating that a large number of oestrogen-like pollutants, all present at low levels, can act together to add to the internal oestrogenic load.

Male reproductive disorders in humans and prenatal indicators of estrogen exposure

Male reproductive disorders in humans and prenatal indicators of estrogen exposure. A review of published epidemiological studies. Reports of an increase in male reproductive disorders in several countries led to the hypothesis that estrogens during fetal life may cause reduced sperm counts, cryptorchidism, hypospadias and testicular cancer. So far the hypothesis is based on animal studies and reports from the wild life. We systematically searched the epidemiological literature for evidence linking indicators of prenatal serum levels of maternal estrogens with sperm density, hypospadias, cryptorchidism and testicular cancer in humans. Indicators of fetal estrogen exposure included direct measurements, recorded intake of hormones (diethylstilbestrol (DES), oral contraceptives (OCs) and estrogens), pregnancy conditions with known deviant estrogen level as for instance twin pregnancies and some environmental exposures. Among 425 papers we reviewed 81 publications with appropriate information. With the possible exception of testicular cancer there is no strong epidemiological evidence to indicate that prenatal exposure to estrogen are linked to disturbed development of the male reproductive organs.

Comparison of serum FSH and Inhibin B levels between adult male dizygotic and monozygotic twins

BACKGROUND

FSH hypersecretion occurs in mothers of dizygotic (DZ) twins. Twinning is inherited via both sexes and transmitted through the female. FSH hypersecretion may thus occur in male DZ twins.

METHODS

We assayed FSH and its counter-regulatory hormone, Inhibin B, in 108 adult male DZ and 100 monozygotic (MZ) twins (as controls) and compared our results to published norms.

RESULTS

Inhibin B was elevated and higher in DZ compared with MZ twins with similar FSH.

CONCLUSION

The normal FSH: Inhibin B endocrine feedback axis is different in adult male DZ twins. This contributes to the theory that the answer to human DZ twinning lies in the actions of FSH and Inhibin, and in their mutual interaction.

Maternal hormone levels and risk of cryptorchism among populations at high and low risk of testicular germ cell tumors

Cryptorchism is one of the few well-described risk factors for testicular cancer. It has been suggested that both conditions are related to increased in utero estrogen exposure. The evidence supporting the "estrogen hypothesis" has been inconsistent, however. An alternative hypothesis suggests that higher in utero androgen exposure may protect against the development of cryptorchism and testicular cancer. In order to examine both hypotheses, we studied maternal hormone levels in two populations at diverse risks of testicular cancer; Black Americans (low-risk) and White Americans (high-risk). The study population of 200 mothers of cryptorchid sons and 200 mothers of noncryptorchid sons was nested within the Collaborative Perinatal Project, a cohort study of pregnant women and their children. Third trimester serum levels of estradiol (total, free, bioavailable), estriol, testosterone (total, free, bioavailable), sex hormone-binding globulin, alpha-fetoprotein, and the ratios of estradiols to testosterones were compared between the case and control mothers. The results found no significant differences in the levels of testosterone (total, free, bioavailable), alpha-fetoprotein, sex hormone-binding globulin, or in the ratios of estrogens to androgens. Total estradiol, however, was significantly lower in the cases versus the controls (P = 0.03) among all mothers and, separately, among White mothers (P = 0.05). Similarly, estriol was significantly lower among all cases (P = 0.05) and among White cases (P = 0.05). These results do not support either the estrogen or the androgen hypothesis. Rather, lower estrogens in case mothers may indicate that a placental defect increases the risk of cryptorchism and, possibly, testicular cancer.

Systematic review of the relationship between family history and lung cancer risk

We performed a systematic review of 28 case-control, 17 cohort and seven twin studies of the relationship between family history and risk of lung cancer and a meta-analysis of risk estimates. Data from both case-control and cohort studies show a significantly increased lung cancer risk associated with having an affected relative. Risk appears to be greater in relatives of cases diagnosed at a young age and in those with multiple affected family members. Increased lung cancer risk was observed in association with an affected spouse and twin studies, while limited, favour shared environmental exposures. The limitations of the currently published epidemiological studies to infer genetic susceptibility are discussed.

Perinatal exposure to bisphenol-A alters peripubertal mammary gland development in mice

Developmental exposure to estrogenic chemicals induces morphological, functional, and behavioral anomalies associated with reproduction. Humans are exposed to bisphenol-A (BPA), an estrogenic compound that leaches from dental materials and plastic food and beverage containers. The aim of the present study was to determine the effects of perinatal exposure to low, environmentally relevant doses of BPA [25 and 250 ng BPA/kg body weight (bw).d] on the peripubertal development of the mammary gland. BPA exposure enhanced the mammary glands' sensitivity to estradiol in ovariectomized CD-1 mice. In their intact 30-d-old littermates, the area and numbers of terminal end buds relative to the gland ductal area increased whereas their apoptotic activity decreased. There was a positive correlation between ductal length and the age at first proestrus; that was reduced as the BPA dose increased, suggesting that BPA exposure slows down ductal invasion of the stroma. There was also a significant increase of progesterone receptor-positive ductal epithelial cells that were localized in clusters, suggesting future branching points. Indeed, lateral branching was significantly enhanced at 4 months of age in mice exposed to 25 ng BPA /kg bw.d. In conclusion, perinatal exposure to environmentally relevant BPA doses results in persistent alterations in mammary gland morphogenesis. Of special concern is the increased terminal end bud density at puberty as well as the increased number of terminal ends reported previously in adult animals, as these two structures are the sites at which cancer arises in humans and rodents.

Breast cancer incidence in women prenatally exposed to maternal cigarette smoke

BACKGROUND

Clinical studies show that maternal cigarette smoking reduces pregnancy estrogen levels. Women prenatally exposed to maternal cigarette smoke may, therefore, have a lower breast cancer risk because the fetal mammary gland's exposure to maternal estrogen is decreased. Associations between prenatal maternal cigarette smoke exposure and breast cancer, however, have not been observed in previous case-control studies that relied on exposure assessment after the onset of cancer. At the start of this study, cigarette smoking history was obtained directly from the mother.

METHODS

The National Cooperative DES Adenosis project was a follow-up study of health outcomes in women prenatally exposed to diethylstilbestrol (DES). At the start of the study, women's mothers provided information about cigarette smoking habits during the time they were pregnant with the study participant. In the current study, the breast cancer rates are compared among 4031 women who were or were not prenatally exposed to maternal cigarette smoke. The resultant relative rate (RR) is adjusted for potential confounding by other breast cancer risk factors using Poisson regression modeling.

RESULTS

Fetal exposure to maternal cigarette smoke appeared to be inversely associated with breast cancer incidence (RR = 0.49; 95% confidence interval [CI] = 0.24-1.03). The inverse association was more apparent among women whose mothers smoked 15 cigarettes or fewer per day than among daughters of heavier smokers. There were, however, too few cases to precisely estimate a possible dose-response relationship.

CONCLUSION

These results support the hypothesis that in utero exposure to maternal cigarette smoke reduces breast cancer incidence.

Childhood and Adult Cancer in Twins: Evidence from the Utah Genealogy

OBJECTIVE

Evidence suggests that the in utero environment may contribute to subsequent development of cancers in childhood and adulthood. Raised levels of estrogen during pregnancy may be the primary in utero etiologic factor. Mothers of twins have higher estrogen levels during pregnancy than mothers of singletons, therefore, assessment of cancer risk in twins may be informative.

METHOD

We conducted a retrospective cohort study of cancer among twin and singleton newborns selected from the Utah Population Database, matched on birth year and sex. Cancer diagnoses were determined by linkage with the Utah state cancer register. Relative rates of all cancers in childhood and in adulthood in twins compared with singletons, and for specific cancers including testicular, breast and melanoma, were calculated using Poisson regression.

RESULTS

Twin (35,271) and singleton (74,199) births were identified, among whom there were 336 and 691 cancer diagnoses, respectively. The relative risk (RR) of childhood cancer in twins compared with singletons was 0.82 [95% confidence interval (CI) 0.55-1.24] and of adult cancer was 1.06 (0.92-1.22). We found nonsignificant increases in risk among adult twins for cancers of the breast, prostate, testis, lymphatic system, thyroid, and large bowel. The largest departures from unity were for testicular cancer (RR 1.47; 95% CI, 0.73-2.95) and melanoma (RR 0.67; 95% CI, 0.42-1.06).

CONCLUSIONS

These results are consistent with the body of evidence suggesting that twins have a reduced risk of cancer in childhood. Although there is no overall differential in adult cancer risk, these data support the hypothesis that the in utero environment may play an important role in specific cancers.

In utero exposures and the incidence of endometriosis

OBJECTIVE

To investigate the relation between the fetal environment and endometriosis.

DESIGN

Prospective cohort study.

SETTING

Nurses' Health Study II with 10 years of follow-up.

PARTICIPANT(S)

Eighty-four thousand, four hundred forty-six women aged 25-42 who had never been diagnosed with endometriosis, infertility, or cancer at baseline in 1989.

MAIN OUTCOME MEASURE(S)

Incidence of laparoscopically confirmed endometriosis according to birthweight, prematurity, multiple gestation, diethylstilbestrol (DES) exposure, and having been breastfed.

RESULT(S)

During 566,250 woman-years of follow-up, 1,226 cases of laparoscopically-confirmed endometriosis were reported among women with no past infertility. After adjusting for age, calendar time, parity, race, and body mass index at age 18, we observed a linear increase in the incidence rate with decreasing birthweight (rate ratio [RR] = 1.3 for birthweight <5.5 pounds versus 7.0-8.4 pounds, 95% confidence interval [CI] = 1.0-1.8, P value, test for trend = .01). In addition, women who were born as one of a multiple gestation (i.e., twins or greater number) were at increased risk even after controlling for birthweight (RR = 1.7, CI = 1.2-2.5). The rate of endometriosis was also 80% greater among women exposed to diethylstilbestrol in utero (RR = 1.8, CI = 1.2-2.8). Neither premature delivery nor having been breastfed were associated with the incidence of endometriosis. None of these effect estimates were modified by infertility status at the time of endometriosis diagnosis.

CONCLUSION(S)

The fetal environment is associated with subsequent laparoscopically confirmed endometriosis in this cohort of US women.

Gender mix in twins and fetal growth, length of gestation and adult cancer risk

This study evaluated the effect of gender mix (the gender combinations of twin pairs) on fetal growth and length of gestation, and reviewed the literature on the long-term effects of this altered fetal milieu on cancer risk. In singletons, it is well established that females weigh less than males at all gestations, averaging 125-135 g less at full term. This gender difference is generally believed to be the result of the effect of androgens on fetal growth. The gender difference in fetal growth is greater before the third trimester and less towards term, with males growing not only more, but also earlier than females. Plurality is a known risk factor for reduced fetal growth and birthweight. Compared with singletons, the mean birthweight percentiles of twins fall substantially (by 10% or more) below the singleton 10th percentile by 28 weeks, below the singleton 50th percentile by 30 weeks, and below the singleton 90th percentile by 34 weeks. In unlike-gender twin pairs, it has been reported that the female prolongs gestation for her brother, resulting in a higher birthweight for the male twin than that of like-gender male twins. Other researchers have demonstrated that females in unlike-gender pairs had higher birthweights than females in like-gender pairs. Analyses from our consortium on 2491 twin pregnancies with known chorionicity showed longer gestations and faster rates of fetal growth in both males and females in unlike-gender pairs compared with like-gender male or female pairs, although these differences were not statistically significant. The post-natal effects for females growing in an androgenic-anabolic environment include increased sensation-seeking behaviour and aggression, lowered visual acuity, more masculine attitudes and masculinising effects of the auditory system and craniofacial growth. In contrast, there is no evidence to suggest that there might be a similar feminising effect on males from unlike-gender pairs. This hormonal exposure in utero may influence adult body size and susceptability to breast cancer.

Is there an association between maternal weight and the risk of testicular cancer? An epidemiologic study of Norwegian data with emphasis on World War II

Since registration started in the 1950s, the incidence of testicular cancer (TC) in the Western world has increased, which is also the case in Norway. Men born in Norway during World War II (WWII), however, have a lower TC incidence than men born in the years before or after WWII. Increased fetal exposure to estrogen during the first trimester of pregnancy has been proposed as a risk factor for the development of TC later in life. Increased maternal weight is associated with higher insulin levels, leading to lower sex hormone-binding globulin levels and thereby increased levels of bioavailable estrogens for transplacental transfer from mother to fetus. The aim of the present study was therefore to examine whether there was an association between maternal weight and the incidence of TC among those who were born in a time period where the nutritional conditions changed, i.e., around the time of WWII. We compared data for a random sample of women giving birth in Oslo, Norway, in the years 1931 to 1955 with the TC incidence among men born in the whole country in the same time period. Maternal weight at delivery was used as a proxy for first-trimester weight. We found a correlation (Spearman's rho = 1.00, p < 0.01; Pearson's r = 0.95, p = 0.02) between the TC incidence and maternal weight adjusted for birth weight and maternal age. Although one cannot draw firm conclusions from ecologic correlations, these findings suggest that the increase in TC incidence over the past decades could be at least partly attributed to the increased maternal body weight observed in most populations in the relevant time period since TC is thought to be associated with in utero conditions.

Epidemiology of testicular cancer: An overview

Testicular cancer is a rare disease, accounting for 1.1% of all malignant neoplasms in Canadian males. Despite the low overall incidence of testicular cancer, it is the most common malignancy among young men. The incidence rate of testicular cancer has been increasing since the middle of the 20th century in many western countries. However, the etiology of testicular cancer is not well understood. A search of the peer-reviewed literature was conducted to identify important articles for review and inclusion in this overview of the epidemiology of testicular cancer. Most of the established risk factors are related to early life events, including cryptorchidism, carcinoma in situ and in utero exposure to estrogens. Occupational, lifestyle, socioeconomic and other risk factors have demonstrated mixed associations with testicular cancer. Although there are few established risk factors for testicular cancer, some appear to be related to hormonal balance at various life stages. Lifestyle and occupational exposures occurring later in life may play a role in promoting the disease, although they are not likely involved in cancer initiation. In addition to summarizing the current epidemiologic evidence on risk factors for testicular cancer, we suggest future research directions that may elucidate the etiology of testicular cancer.

In utero alcohol exposure increases mammary tumorigenesis in rats

Findings in humans and animal models suggest that in utero hormonal and dietary exposures increase later breast cancer risk. Since alcohol intake by adult women consistently increases their breast cancer risk, we wondered whether maternal alcohol consumption during pregnancy increases female offspring's mammary tumorigenesis. In our study, pregnant female rats were pair-fed isocaloric diets containing either 0 (control), 16 or 25 g alcohol kg(-1) feed between days 7 and 19 of gestation. These alcohol exposures generate blood alcohol levels that correspond to low and moderate alcohol consumption and are lower than those that induce foetal alcohol syndrome. Serum oestradiol levels were elevated in pregnant rats exposed to alcohol (P<0.003). When adult, female offspring of alcohol-exposed dams developed significantly more 7,12-dimethylbenz[a]anthracene -induced mammary tumours, compared to the controls (tumour multiplicity; mean+/-s.e.m., controls: 2.0+/-0.3, 16 g alcohol: 2.7+/-0.4 and 25 g alcohol: 3.7+/-0.4; P<0.006). In addition, the mammary epithelial tree of the alcohol-exposed offspring was denser (P<0.004) and contained more structures that are susceptible for the initiation of breast cancer (P<0.001). Immunohistochemical assessment indicated that the mammary glands of 22-week-old in utero alcohol-exposed rats contained elevated levels of oestrogen receptor-alpha (P<0.04) that is consistent with the changes in mammary gland morphology. In summary, maternal alcohol intake during pregnancy increases female offspring's mammary tumorigenesis, perhaps by programming the foetal mammary gland to exhibit persistent alterations in morphology and gene expression. It remains to be determined whether an increase in pregnancy oestradiol levels mediated alcohol's effects on offspring's mammary tumorigenesis.

Clinical epidemiology of testicular germ cell tumors

Clinical epidemiology is sometimes called the basic science of clinical medicine. In terms of the pathogenesis of testicular germ cell tumors (GCTs), clinical epidemiology analyzes suspected risk factors. The present review highlights the risk factors established so far and briefly summarizes those factors currently under investigation. In analogy to the methods of evidence based medicine, this review attributes levels of evidence to each of the putative risk factors. Level I represents highest quality of evidence while level V denotes the lowest level. So far, undescended testis (UDT), contralateral testicular GCT and familial testis cancer are established risk factors attaining high levels of evidence (levels I-III a). In a meta-analysis of 21 studies exploring the association of UDT with GCT risk, an over-all relative risk (RR) of 4.8 (95% confidence interval 4.0-5.7) was found. Contralateral testicular GCT involves a roughly 25-fold increased RR of GCT, while familial testis cancer constitutes a RR of 3-10. Infertility, testicular atrophy, and twin-ship represent risk factors with lesser levels of evidence (level III a). There is also some evidence for HIV infection being a predisposing factor for GCT (level IV a). Scrotal trauma is probably not associated with GCT risk. The estrogen excess theory implies high estrogen levels during the first trimester of pregnancy. As a consequence, primordial germ cells lose track of the normal developmental line and transform into premalignant cells that later become testicular intraepithelial neoplasia (TIN), the precursor of full-blown testicular GCT. Surrogate parameters for high gestational estrogen levels are investigated in case control studies. Such factors are maternal age >30 years, first-born, low birth weight, maternal breast cancer, high sex-ratio of siblings. So far, the sum of evidence is promising but still conflicting (especially for level III b). Another novel theory is the childhood nutrition hypothesis. This concept postulates a modulating or "catalyzing" effect by high dietary intake during childhood on the pathogenesis of testicular GCT. A surrogate parameter of early childhood nutrition is adult height. So far, 12 controlled studies have looked to the possible association of attained height and GCT risk of which six demonstrated a significant association. Thus, the sum of evidence corresponds to level III b. This concept is appealing because it would explain several hitherto unexplained epidemiological features of GCT.

Genetic Variations in the Vitamin D Receptor, Androgen Receptor and Enzymes that Regulate Androgen Metabolism

PURPOSE

We review the current literature on genetic variations in the vitamin D receptor (VDR), androgen receptor (AR) and enzymes regulating androgen development.

MATERIALS AND METHODS

A MEDLINE search was conducted to identify research investigating associations between polymorphisms in important regulatory genes that may indirectly affect cancer risk, with special regard to prostate cancer.

RESULTS

Genes involved in androgen regulation, metabolism and their related pathways, and the vitamin D receptor are prime candidates for study of prostate cancer risk. Expression and nuclear activation of the VDR are necessary for the antiproliferative effects of 1alpha,25-dihydroxyvitamin D3 (calcitriol), which is involved in calcium and bone homeostasis. Several genetic variations have been identified in the VDR, and at least 1 VDR polymorphism appears to confer some predictability of prostate cancer risk in various ethnic cohorts. Interactions between the androgen receptor and circulating androgens have a major role in the development of normal and malignant prostate cells.

CONCLUSIONS

Due to the relationship between the AR and prostatic growth, it has been proposed that polymorphisms within the AR may have a role in susceptibility to prostate cancer.

A case-control study of dietary phytoestrogens and testicular cancer risk

A few dietary studies have found elevated testicular cancer risks for higher red meat, fat, and milk intakes and lower intakes of fruits, vegetables, and fiber. Because hormonal modulation by dietary intake of plant estrogens could affect risk of testicular cancer, we chose to explore the possible relationship between dietary phytoestrogens and testicular cancer. We conducted a hospital-based case-control study of 159 testicular cancer cases diagnosed between 1990 and 1996 and 136 adult friend-matched controls at the University of Texas M. D. Anderson Cancer Center. Amounts of phytoestrogenic compounds in foods were added to the National Cancer Institute's DietSys program and then grouped into prelignans, lignans, flavonoids, isoflavonoids, phytosterols, and coumestrol for statistical analysis, expressed per 1,000 kcal. The results of multivariate logistic regression analysis showed, after adjustment for age, education, income, ethnicity, cryptorchidism, body mass index, baldness unrelated to therapy, severe acne in adolescence, early puberty, daily fiber and fat intake, and total daily calories, no discernable monotonic increased or decreased risk estimates across quartiles of phytoestrogen intake. A U-shaped pattern was observed for lignans and coumestrol. Further evaluation of this pattern by cubic spline parameterization did fit the data, but the data were also consistent with no effect. This hypothesis-generating study does not support the premise that dietary phytoestrogens increase or decrease testicular cancer risk in young men.

The 'oestrogen hypothesis'- where do we stand now?

The original 'oestrogen hypothesis' postulated that the apparent increase in human male reproductive developmental disorders (testis cancer, cryptorchidism, hypospadias, low sperm counts) might have occurred because of increased oestrogen exposure of the human foetus/neonate; five potential routes of exposure were considered. This review revisits this hypothesis in the light of the data to have emerged since 1993. It addresses whether there is a secular increasing trend in the listed disorders and highlights the limitations of available data and how these are being addressed. It considers whether new data has emerged to support the suggestion that increased oestrogen exposure could cause these abnormalities and reviews new data on potential routes via which such increased exposure could have occurred. Secular trends: The disorders listed above are now considered to represent a syndrome of disorders (testicular dysgenesis syndrome, TDS) with a common origin in foetal life. Testicular cancer has increased in incidence in Caucasian men worldwide and lifetime risk is 0.3-0.8%. Secular trends in cryptorchidism are unclear but it is by far the commonest (2-4% at birth) congenital abnormality in either sex. Secular trends for hypospadias are not robust, although most studies suggest a progressive increase; registry data probably under-estimates incidence, but based on this data hypospadias is the second most common (0.3-0.7% at birth) congenital malformation. Retrospective analyses of sperm count data show a global downward trend but this is inconclusive - prospective studies using standardized methodology show significant differences between countries and very low sperm counts in the youngest cohort of men. For all disorders, other then testis cancer, standardized prospective studies are the best way forward and are in progress across Europe. Oestrogen effects: Evidence that foetal exposure to oestrogens can induce the above disorders has strengthened. New pathways via which such changes could be induced have been identified, including suppression of testosterone production by the foetal testis, suppression of androgen receptor expression and suppression of insulin-like factor-3 (InsL3) production by foetal Leydig cells. Other evidence suggests that the balance between androgen and oestrogen action may be important in induction of reproductive tract abnormalities. Oestrogen exposure: Although many new environmental oestrogens have been identified, their uniformly weak oestrogenicity excludes the possibility that they could induce the above disorders. However, emerging data implicates various environmental chemicals in being able to alter endogenous levels of androgens (certain phthalates) and oestrogens (polychlorinated biphenyls, polyhalogenated hydrocarbons), and the former have been shown to induce a similar collection of disorders to TDS. Other mechanisms via which increased fetal exposure to pregnancy oestrogens might occur (increasing trend in obesity, dietary changes) are also discussed.

Differential expression of two estrogen receptor beta isoforms in the human fetal testis during the second trimester of pregnancy

Testicular cancer is more common in individuals with disorders of the male reproductive tract. It has been suggested that inappropriate exposure to estrogens during fetal life may have an impact on maturation of testicular germ cells that are the cells of origin of the majority of testis cancers. The aim of the present study was to establish whether human fetal germ cells (gonocytes) are a potential target of estrogen action. To address this issue, we used RT-PCR and immunohistochemistry to examine the pattern of expression of estrogen receptors (ER alpha, ER beta, and ER beta 2 variant) in human fetal testes at 12-19 wk gestation. ER alpha, mRNA, and protein were not detected in any of the fetal testes. In contrast, using an antibody directed against the hinge domain of ER beta expression was detected in multiple testicular nuclei. RT-PCR with primers specific for full-length wild-type ER beta (ER beta 1) or the ER beta 2 variant formed by splicing of an alternative eighth exon, was performed on whole-tissue extracts and materials recovered by laser capture and revealed that mRNAs for both isoforms were expressed. Immunohistochemistry with isotype-specific monoclonal antibodies showed that ER beta 1 was low/undetectable in gonocytes, whereas these cells expressed the highest levels of ER beta 2, compared with other testicular cell types. Both ER beta 1 and ER beta 2 were detected in some but not all Sertoli cells, peritubular cells, and other interstitial cells including those tentatively identified as Leydig cells. Our immunohistochemical results demonstrate that during the second trimester, some but not all somatic cells within the human fetal testis express wild-type ER beta (ER beta 1) protein and/or the variant isoform of ER beta (ER beta 2) that lacks amino acids essential for binding of estradiol. ER beta 2 protein was readily detectable in fetal gonocytes, whereas ER beta 1 was not. We did not detect expression of ER alpha. The expression of ER beta 2, a variant proposed act as a dominant negative receptor, might prevent estrogen action in gonocytes. We suggest that during this period of fetal life, estrogenic ligands are most likely to act on somatic cells that contain ER beta 1 protein.

Male reproductive disorders and the role of endocrine disruption: Advances in understanding and identification of areas for future research

This review addresses whether there is a secular increasing trend in male reproductive developmental disorders (cryptorchidism, hypospadias, testis cancer, low sperm counts), and highlights the limitations of available data and how these issues are being addressed. These disorders are considered to represent a syndrome of disorders [testicular dysgenesis syndrome (TDS)] with a common origin in fetal life, and in which "endocrine disruption" plays a central role. The potential involvement of environmental estrogens in the etiology of these disorders is reviewed in light of new understanding about the pathways and dose-effect relationships of estrogen action on male reproductive development. Several new pathways of estrogen action have been identified, including suppression of the production of testosterone and insulin-like factor-3 by fetal/neonatal Leydig cells and suppression of androgen receptor expression in androgen target tissues. It is tentatively concluded that identified environmental chemicals are unlikely to activate these pathways because of their intrinsically weak estrogenicity. However, chemicals that may alter endogenous estrogen production, bioavailability, or inactivation represent a new focus of concern. Additionally, environmental chemicals that alter endogenous levels of androgens in the rat fetus (certain phthalates) induce a similar collection of disorders to TDS. Whether human exposure to such compounds might contribute to TDS remains to be shown, but studies in animals should help to define susceptible pathways for induction of TDS.

Infertility and environmental pollutants

While it has long been known that female fertility is impaired by oestrogen exposure, it is unclear whether environmental pollutants with weak oestrogenic effects are sufficiently potent and prevalent to have biological effects in humans. Male fertility, or sperm concentration at least, appears to have deteriorated, and there is substantial spatial variation at both national and global level, as well as a genetic component. Sperm morphology and motility are implicated too. There is good evidence for an increase in testicular cancer, and possibly in other conditions that certain spatial characteristics plus evidence on heritability suggest are linked to impaired spermatogenesis. A candidate agent would need to have started increasing in the early 20th century. Weak environmental oestrogens are not responsible. Candidates include agents affecting endogenous maternal oestrogen levels, environmental anti-androgens (although these cannot explain the epidemiological findings), and dioxin and related compounds. Genetic damage should be considered as a unifying hypothesis, possibly focused on the Y-chromosome.

Lifetime prevalence and characteristics of recurrent primary headaches in a population-based sample of Swedish twins

OBJECTIVE

To examine the lifetime prevalence and other characteristics of recurrent primary headaches in twins.

BACKGROUND

The twin model may provide insights into the role of genetic and environmental influences in headache disorders. However, assumptions as to whether twins are representative of the general population, and whether monozygotic and dizygotic twins are similar have rarely been addressed.

METHODS

The study population consisted of a random sample of 17- to 82-year-old twins from the Swedish Twin Registry (n = 1329). Structured interviews on the telephone by lay personnel and the International Headache Society criteria were used for assessment and diagnosis of recurrent primary headaches. Prevalence data of the general population for migraine and tension-type headache was obtained from various published reports.

RESULTS

A total of 372 subjects (29%) had ever had recurrent headaches. In total, 241 recurrent headache sufferers fulfilled the criteria for migraine or tension-type headache, and the lifetime prevalence was 7.1% for migraine without aura, 1.4% for migraine always with aura, 1.9% for migraine occasionally with aura, 9.4% for episodic tension-type headache, and 1.3% for chronic tension-type headache. The lifetime prevalence of all migraine and all tension-type headache, including another 84 subjects fulfilling all but one of the criteria for migraine or tension-type headache, was 13.8% and 13.5%, respectively. The corresponding prevalence risk for women was 2.4 (95% confidence interval [CI] 1.7, 3.4) and 1.5 (95% CI 1.1, 2.1), respectively. Zygosity was not a significant predictor for migraine. In tension-type headache, the prevalence risk for dizygotic twins and unlike-sexed twins as compared with monozygotic twins was 1.9 (95% CI: 1.2, 3.1) and 1.8 (95% CI: 1.1, 2.9), respectively.

CONCLUSION

There is no twin-singleton or monozygotic-dizygotic difference for the risk of migraine. In tension-type headache, twins seem to have a lower risk than singletons, and this is especially true for monozygotic twins.

The Swedish Twin Registry: a unique resource for clinical, epidemiological and genetic studies

The Swedish Twin Registry (STR), which today has developed into a unique resource, was first established in the late 1950s to study the importance of smoking and alcohol consumption on cancer and cardiovascular diseases whilst controlling for genetic propensity to disease. Since that time, the Registry has been expanded and updated on several occasions, and the focus has similarly broadened to most common complex diseases. In the following, we will summarize the content of the database, describe for the first time recent data collection efforts and review some of the principal findings that have come from the Registry.

Do estrogens always increase breast cancer risk?

The etiology of breast cancer is closely linked to the female hormone estrogen, with high life-time exposure being suggested to increase breast cancer risk [Nature 303 (1983) 767]. However, there appears to be a disparity between studies attempting to establish an association between high estrogen levels and breast cancer risk. This disparity becomes smaller by taking into consideration a timing factor, and we propose that estrogens can increase, decrease, or have no effect on breast cancer risk, depending on the timing of estrogen exposure. We further propose that the timing of estrogenic exposures may play at least as important a role in affecting breast cancer risk as life-time exposure.

Tallness and overweight during childhood have opposing effects on breast cancer risk

Using birth and school health records we studied how weight and height during childhood affect breast cancer risk among 3447 women born during 1924-33 at the University Hospital of Helsinki, Finland. Through linkages with the National Hospital Discharge Registry and the Cause of Death Registry we identified 177 women who during 1971-1995 had been admitted to hospital with breast cancer, of whom 49 had died from the disease. Of these, 135 (76%) were aged 50 years or more at the time of diagnosis, and therefore likely to have been post-menopausal. Hazard ratios for breast cancer rose with increasing weight and length at birth, though neither trend was statistically significant. At each age, from 7 to 15 years, the girls who later developed breast cancer were on average taller and had lower body mass than the other girls. Unadjusted hazard ratios rose across the range of height (P = 0.01 at age 7 years) and fell across the range of body mass index (P = 0.009 at age 7 years). In a simultaneous analysis the hazard ratio for breast cancer was 1.27 (95% CI 0.97-1.78, P = 0.08) for every kilogram increase in birth weight and 1.21 (95% CI 1.06-1.38, P = 0.004) for every kg/m(2) decrease in body mass index at 7. Our findings indicate that tallness in childhood is associated with increased risk of developing breast cancer. One possible explanation is persisting high plasma concentrations of insulin-like growth factors in tall women. In contrast, we found that being overweight in childhood reduces breast cancer risk. The increased adipose tissue-derived oestrogen levels in overweight children could induce early breast differentiation and eliminate some targets for malignant transformation.

In utero exposure to bisphenol A alters the development and tissue organization of the mouse mammary gland

Exposure to estrogens throughout a woman's life, including the period of intrauterine development, is a risk factor for the development of breast cancer. The increased incidence of breast cancer noted during the last 50 years may have been caused, in part, by exposure of women to estrogen-mimicking chemicals that are released into the environment. Here, we investigated the effects of fetal exposure to one such chemical, bisphenol A (BPA), on development of the mammary gland. CD-1 mice were exposed in utero to low, presumably environmentally relevant doses of BPA (25 and 250 microg/kg body weight), and their mammary glands were assessed at 10 days, 1 mo, and 6 mo of age. Mammary glands of BPA-exposed mice showed differences in the rate of ductal migration into the stroma at 1 mo of age and a significant increase in the percentage of ducts, terminal ducts, terminal end buds, and alveolar buds at 6 mo of age. The percentage of cells that incorporated BrdU was significantly decreased within the epithelium at 10 days of age and increased within the stroma at 6 mo of age. These changes in histoarchitecture, coupled with an increased presence of secretory product within alveoli, resemble those of early pregnancy, and they suggest a disruption of the hypothalamic-pituitary-ovarian axis and/or misexpression of developmental genes. The altered relationship in DNA synthesis between the epithelium and stroma and the increase in terminal ducts and terminal end buds are striking, because these changes are associated with carcinogenesis in both rodents and humans.

Cancer risk in men exposed in utero to diethylstilbestrol

BACKGROUND

An association between prenatal diethylstilbestrol (DES) exposure and cancer in men, especially testicular cancer, has been suspected, but findings from case-control studies have been inconsistent. This study was conducted to investigate the association between prenatal DES exposure and cancer risk in men via prospective follow-up.

METHODS

A total of 3613 men whose prenatal DES exposure status was known were followed from 1978 through 1994. The overall and site-specific cancer incidence rates among the DES-exposed men were compared with those of the unexposed men in the study and with population-based rates. The relative rate (RR) was used to assess the strength of the association between prenatal DES exposure and cancer development. All statistical tests were two-sided.

RESULTS

Overall cancer rates among DES-exposed men were similar to those among unexposed men (RR = 1.07; 95% confidence interval [CI] = 0.58 to 1.96) and to national rates (RR = 0.99; 95% CI = 0.65 to 1.44). Testicular cancer may be elevated among DES-exposed men, since the RRs for testicular cancer were 3.05 (95% CI = 0.65 to 22.0) times those of unexposed men in the study and 2.04 (95% CI = 0.82 to 4.20) times those of males in the population-based rates. The higher rate of testicular cancer in the DES-exposed men is, however, also compatible with a chance observation.

CONCLUSIONS

To date, men exposed to DES in utero do not appear to have an increased risk of most cancers. It remains uncertain, however, whether prenatal DES exposure is associated with testicular cancer.

Mortality among women and men relative to unemployment, part time work, overtime work, and extra work: a study based on data from the Swedish twin registry

OBJECTIVE

To examine mortality before 70 years of age among women and men relative to unemployment, part time work, overtime work, and extra work. Age, marital status, children, smoking and alcohol habits, use of sleeping pills and tranquilisers, stress, shift work, personality factors, and long lasting or serious illness were taken into account as potential confounding factors.

METHODS

The study group comprised a subcohort of the Swedish twin registry, people born in 1926-58. Data were based on a postal questionnaire of 1973 and on information from the Swedish Causes of Death Registry. All subjects reporting a main occupation were selected, 9500 women and 11 132 men, and mortality from all causes during 1973-96 was analysed. The subjects were treated as a sample from the general population regardless of the twinning.

RESULTS

Unemployment in 1973 among both women and men showed an association with increased mortality. The adjusted relative risk (RR) (95% confidence interval (95% CI)) was 1.98 (1.16 to 3.38), for women and 1.43 (0.91 to 2.25) for men. For the first 5 years of follow up, a threefold increase in risk was found for men (RR (95% CI) 3.29 (1.33 to 8.17)). The RR declined by time, but remained increased throughout the 24 year study period. In women overtime work of more than 5 hours a week was followed by an increased mortality rate (RR (95% CI) 1.92 (1.13 to 3.25)). A protective effect of moderate overtime work of a maximum 5 hours a week was shown for men (RR (95% CI) 0.58 (0.43 to 0.80)), whereas an increased mortality was indicated for part time work (RR (95% CI) 1.58 (0.91 to 2.77)) and extra work (work outside employment) of more than 5 hours a week (RR (95% CI) 1.29 (0.99 to 1.69)).

CONCLUSION

Unemployment and some time aspects of work were associated with subsequent mortality, even when controlling for social, behavioural, work, and health related factors. The idea that losing a job may have less importance for women than for men is not supported by this study.

High constant incidence in twins and other relatives of women with breast cancer

The incidence of breast cancer rises steeply between ages 25 and 50, and more slowly thereafter. In contrast, the incidence in the unaffected (contralateral) breast of women who have had breast cancer remains constant at about 0.7% per year for at least the next 20 years after diagnosis, irrespective of age at first diagnosis. The incidence in relatives of the patients seems to show a similar pattern. The incidence in a prospective study of monozygotic twins of patients was approximately constant at 1.3% per year (77 cases), again about 0.7% per breast. At ages older than a patient's age at diagnosis, her mother and sisters have an incidence of 0.3-0.4% per year. Above the index patient's age at diagnosis, the rate in relatives shows no temporal trend and is independent of the patient's age at diagnosis. A statistically simple explanation is that incidence in susceptible women increases to a high constant level by a predetermined age that varies between families, but this seems inconsistent with conventional models of carcinogenesis and susceptibility. The very high incidence in monozygotic twins of patients indicates that a high proportion, and perhaps the majority, of breast cancers arise in a susceptible minority of women.

Birthweight, childhood growth and risk of breast cancer in a British cohort

We have examined the relationship between birthweight and risk of breast cancer, taking into account growth in childhood, using data on a total of 2221 women born in 1946 and followed up to 1997. Thirty-seven breast cancers occurred during follow-up. There was evidence of greater risk of breast cancer with greater birthweight (rate ratio = 1.76 (95% CI: 0.92, 3.35) for birthweight >/= 3.5 kg vs birthweight < 3.5 kg), which was more marked at pre-menopausal ages (RR = 2.31, 95% CI: 0.93, 5.74). The relation with birthweight was not substantially confounded by any of the measured adult risk factors. A significant interaction was observed between the effects of birthweight and height at age 7 years. Relative to those born lighter than 3.5 kg, women who were heavy at birth (>/= 3.5 kg) and short or average at 7 years (< 1.22 m) had a 21% increase in breast cancer rates (RR = 1.21; 95% CI = 0.49-2.99), while women who were heavy at birth (>/= 3.5 kg) but tall at 7 years (>/= 1.22 m) had a four-fold increase (RR = 4.01; 95% CI = 1.82-8.83). These results suggest that the effect of birthweight on breast cancer risk may be modulated by childhood growth.

Individual variation in somatic mutations of the glycophorin-A gene in neonates in relation to pre-natal factors

The frequency of somatic mutations of the glycophorin-A (GPA) gene was measured in red blood cells from a series of newborn babies and related to various epidemiological and lifestyle factors in order to identify those factors that might influence the mutation rate before birth. Although there was substantial variation in the mutation frequencies between individual babies, no specific associations were found with any of the factors explored including smoking, age and social class of the parents, and gender and birth weight of the babies. It is concluded that these factors do not have a substantial effect on the mutational endpoint measured, although this does not necessarily mean that they have no effect on health risk to the offspring. The observed variation in GPA gene mutation frequency must, therefore, be due either to exposure to less obvious external influences or to intrinsic factors.

Twinship and risk of postmenopausal breast cancer

BACKGROUND

Intrauterine exposure to high levels of endogenous estrogens has been hypothesized to increase the risk of breast cancer. Because estrogens and other pregnancy hormones are substantially elevated in twin pregnancies, and possibly more so in dizygotic twin pregnancies, we evaluated the association between aspects of twin membership (i.e., belonging to a twin pair) and the risk of breast cancer.

METHODS

In a cohort of 29 197 postmenopausal Iowa women with no prior diagnosis of cancer (except for nonmelanoma skin cancer), breast cancer risk factors were determined by use of a mailed questionnaire in 1986 (baseline); twin membership, sex of the twin, and zygosity were determined by use of a follow-up questionnaire in 1992.

RESULTS

Within the cohort, 1.8% (n = 538) of the women reported being a twin; of these, 24% (n = 130) were monozygotic twins, 63% (n = 337) were dizygotic twins, and 13% (n = 71) did not know their zygosity. From 1986 through 1996, 1230 breast cancers in the cohort were ascertained by linkage to the Iowa Cancer Registry. Compared with singletons, women who belonged to a twin pair were at elevated risk of breast cancer (multivariate-adjusted risk ratio [RR] = 1.72; 95% confidence interval [CI] = 1.22-2.42), with adjustment for educational level, family history of breast cancer, height, body mass index, body fat distribution, age at menarche, age at first live birth, use of hormone replacement therapy, and alcohol use. Multivariate-adjusted risk was elevated (in comparison with singletons) if the sex of the other twin was female (RR = 1.82; 95% CI = 1.20-2.75); however, this risk was limited to female dizygotic twins (RR = 2.14; 95% CI = 1. 21-3.79), since no excess risk was evident for monozygotic twins (RR = 1.04; 95% CI = 0.43-2.50). The risk to women with a male twin was also elevated (RR = 1.49; 95% CI = 0.80-2.78) in comparison with singletons, but this estimate was not statistically significant.

CONCLUSIONS

This cohort study lends further support to the theory that there are important intrauterine influences on carcinogenesis of the breast.

Genetic predisposition, environment and cancer incidence: a nationwide twin study in Finland, 1976-1995

Twin studies integrate genetic and environmental (including physical environment and life-style) information by comparing monozygotic and dizygotic twins for the occurrence of disease. Our objectives were to compare cancer incidence in twins with national rates and to estimate both the probability that co-twins of affected twins may develop cancer and the importance of genetic predisposition and environment in cancer development. The nationwide record linkage of the Finnish Twin Cohort Study, the Finnish Cancer Registry and the Central Population Register allowed the follow-up of 12,941 same-sexed twin pairs for incident primary cancers from 1976 to 1995. Zygosity was determined by use of a validated questionnaire in 1975. Methods included calculation of standardized incidence ratios and concordances and fitting of structural equation models. A total of 1,613 malignant neoplasms occurred in the cohort. The overall cancer incidence among twins resembled that among the general population. Monozygotic co-twins of affected twins were at 50% higher risk than were dizygotic co-twins. Based on genetic modeling, inherited genetic factors accounted for 18% (95% confidence interval 4-32%) of the liability in inter-individual variation in the risk of overall cancer, while non-genetic factors shared by twins accounted for 7% (0-16%) and unique environmental factors for 75% (65-85%). Our results appear to exclude a contribution greater than one-third for genetic predisposition in the development of cancer in the general population, thus pointing to the earlier confirmed substantial role of environment.

The influence of maternal diet on breast cancer risk among female offspring

The induction of breast cancer is a long process, containing a series of biological events that drive a normal mammary cell towards malignant growth. However, it is not known when the initiation of breast cancer occurs. One hypothesis is that a high estrogenic environment during the perinatal period increases subsequent breast cancer risk. There are many sources of extragonadal estrogens, particularly in the diet. The purpose of this paper is to review the evidence that a high maternal intake of dietary fats increases serum estrogens during pregnancy and increases breast cancer risk in daughters. Our animal studies show that a high maternal consumption of corn oil consisting mainly of linoleic acid (omega-6 polyunsaturated fatty acid, PUFA), increases both circulating estradiol (E2) levels during pregnancy and the risk of developing carcinogen-induced mammary tumors among the female rat offspring. A similar increase in breast cancer risk occurs in female offspring exposed to injections of E2 through their pregnant mother. Our data suggest that the mechanisms by which an early exposure to dietary fat and/or estrogens increases breast cancer risk is related to reduced differentiation of the mammary epithelial tree and increased number of mammary epithelial cell structures that are known to the sites of neoplastic transformation. These findings may reflect our data of the reduced estrogen receptor protein levels and protein kinase C activity in the developing mammary glands of female rats exposed to a high-fat diet in utero. In summary, a high dietary linoleic acid intake can elevate pregnancy estrogen levels and this, possibly by altering mammary gland morphology and expression of fat- and/or estrogen-regulated genes, can increase breast cancer risk in the offspring. If true for women, breast cancer prevention in daughters may include modulating the mother's pregnancy intake of some dietary fats.

Male genital cancers

Each type of male genital cancer has features that are unique in diagnosis and treatment. The incidences of these cancers are related to age, race, and environment. Early diagnosis and treatment are documented as important for all male genital cancers except prostate cancer, where this remains a subject of controversy.

Testicular cancer risk and maternal parity: a population-based cohort study

The aim was to study, in a population-based cohort design, whether first-born sons run a higher risk of testicular cancer than later born sons; to investigate whether this difference in risk was affected by birth cohort, age of the son, maternal age, interval to previous delivery and other reproductive factors; and, finally, to evaluate to what extent changes in women's parity over time might explain the increasing incidence of testicular cancer. By using data from the Civil Registration System, a database was established of all women born in Denmark since 1935 and all their children alive in 1968 or born later. Sons with testicular cancer were identified in the Danish Cancer Registry. Among 1015994 sons followed for 15981 967 person-years, 626 developed testicular cancer (443 non-seminomas, 183 seminomas). Later born sons had a decreased risk of testicular cancer (RR = 0.80, 95% CI = 0.67-0.95) compared with first-born sons. The RR was 0.79 (95% CI = 0.64-0.98) for non-seminomas and 0.81 (95% CI = 0.58-1.13) for seminomas. There was no association between testicular cancer risk and overall parity of the mother, maternal or paternal age at the birth of the son, or maternal age at first birth. The decreased risk of testicular cancer among later born sons was not modified by age, birth cohort, interval to the previous birth, sex of the first-born child, or maternal age at birth of the son or at first birth. The increased proportion of first-borns from birth cohort 1946 to birth cohort 1969 only explained around 3% of an approximated two-fold increase in incidence between the cohorts. Our data document a distinctly higher risk of testicular cancer in first-born compared with later born sons and suggest that the most likely explanation should be sought among exposures in utero. The increase in the proportion of first-borns in the population has only contributed marginally to the increase in testicular cancer incidence.

Environmental endocrine modulators and human health: an assessment of the biological evidence

Recently, a great deal of attention and interest has been directed toward the hypothesis that exposure, particularly in utero exposure, to certain environmental chemicals might be capable of causing a spectrum of adverse effects as a result of endocrine modulation. In particular, the hypothesis has focused on the idea that certain organochlorine and other compounds acting as weak estrogens have the capability, either alone or in combination, to produce a variety of adverse effects, including breast, testicular and prostate cancer, adverse effects on male reproductive tract, endometriosis, fertility problems, alterations of sexual behavior, learning disability or delay, and adverse effects on immune and thyroid function. While hormones are potent modulators of biochemical and physiological function, the implication that exposure to environmental hormones (e.g., xenoestrogens) has this capability is uncertain. While it is reasonable to hypothesize that exposure to estrogen-like compounds, whatever their source, could adversely affect human health, biological plausibility alone is an insufficient basis for concluding that environmental endocrine modulators have adversely affected humans. Diethylstilbestrol (DES) is a potent, synthetic estrogen administered under a variety of dosing protocols to millions of women in the belief (now known to be mistaken) that it would prevent miscarriage. As a result of this use, substantial in utero exposure to large numbers of male and female offspring occurred. Numerous studies have been conducted on the health consequences of in utero DES exposure among the adult offspring of these women. There are also extensive animal data on the effects of DES and there is a high degree of concordance between effects observed in animals and humans. The extensive human data in DES-exposed cohorts provide a useful basis for assessing the biological plausibility that potential adverse effects might occur following in utero exposure to compounds identified as environmental estrogens. The effects observed in both animals and humans following in utero exposure to sufficient doses of DES are consistent with basic principles of dose response as well as the possibility of maternal dose levels below which potential non-cancer effects may not occur. Significant differences in estrogenic potency between DES and chemicals identified to date as environmental estrogens, as well as an even larger number of naturally occurring dietary phytoestrogens, must be taken into account when inferring potential effects from in utero exposure to any of these substances. The antiestrogenic properties of many of these same exogenous compounds might also diminish net estrogenic effects. Based on the extensive data on DES-exposed cohorts, it appears unlikely that in utero exposure to usual levels of environmental estrogenic substances, from whatever source, would be sufficient to produce many of the effects (i.e., endometriosis, adverse effects on the male reproductive tract, male and female fertility problems, alterations of sexual behavior, learning problems, immune system effects or thyroid effects) hypothesized as potentially resulting from exposure to chemicals identified to date as environmental estrogens.

Risks of breast and testicular cancers in young adult twins in England and Wales: evidence on prenatal and genetic aetiology

BACKGROUND

Aetiology of breast and testicular cancers may have prenatal factors, possibly exposure of the fetus to high concentrations of maternal oestrogen. Dizygotic twinning probably involves high hormone concentrations, and therefore, dizygotic twins might be at raised risk of these cancers. The aetiologies of breast and testicular cancers have genetic components, for breast cancer, especially at younger ages. Twins of these probands may, therefore, be at high risk. We investigated risk in twins of patients with breast cancer at young ages or with testicular cancer.

METHODS

We identified twins with breast cancer incident at ages younger than 45 years and with incident testicular cancer in England and Wales during 1971-89 by cross-matching national cancer-registration and births records. We determined zygosity by questionnaires to the patients. The twins of probands were followed up for cancer incidence and death. We analysed risks of breast and testicular cancer in dizygotic twins compared with monozygotic twins, and in monozygotic and dizygotic twins of probands.

FINDINGS

We identified 500 twins with breast cancer and 194 with testicular cancer. We found a non-significantly raised risk of breast cancer in dizygotic compared with monozygotic twins younger than 30 years (odds ratio 2.3 [95% CI 0.9-5.9]) but not older. The overall risk of testicular cancer was significantly higher in dizygotic twins than in monozygotic twins (1.5 [1.1-2.2]) consequent on a risk for seminomas was high (3.2 [1.6-6.5]; p = 0.001). Risk of breast cancer was significantly raised in female twins of probands (standardised incidence ratio 7.7 [4.9-12.2], p < 0.001). The relative risk of breast cancer was 34.7 (9.5-126.5) in monozygotic twins of women in whom breast cancer had occurred before age 35 years. The cumulative risk of breast cancer for these twins by age 40 years was 29% (13-56). The relative risk of testicular cancer was 37.5 (12.3-115.6) in twins of men with testicular cancer. The cumulative risk by age 40 years in monozygotic twins of men with testicular cancer was 14% (4-46).

INTERPRETATION

The higher risks of these cancers in dizygotic than in monozygotic twins support a prenatal aetiology, and are compatible with aetiology related to raised maternal concentrations of free, unbound oestrogens. The results for twins of probands have implications for genetic aetiology; appropriate clinical action for monozygotic twins needs consideration.

A maternal diet high in n - 6 polyunsaturated fats alters mammary gland development, puberty onset, and breast cancer risk among female rat offspring

We hypothesized that feeding pregnant rats with a high-fat diet would increase both circulating 17beta-estradiol (E2) levels in the dams and the risk of developing carcinogen-induced mammary tumors among their female offspring. Pregnant rats were fed isocaloric diets containing 12% or 16% (low fat) or 43% or 46% (high fat) of calories from corn oil, which primarily contains the n - 6 polyunsaturated fatty acid (PUFA) linoleic acid, throughout pregnancy. The plasma concentrations of E2 were significantly higher in pregnant females fed a high n - 6 PUFA diet. The female offspring of these rats were fed with a laboratory chow from birth onward, and when exposed to 7,12-dimethylbenz(a)anthracene had a significantly higher mammary tumor incidence (60% vs. 30%) and shorter latency for tumor appearance (11.4 +/- 0.5 weeks vs. 14.2 +/- 0.6 weeks) than the offspring of the low-fat mothers. The high-fat offspring also had puberty onset at a younger age, and their mammary glands contained significantly higher numbers of the epithelial structures that are the targets for malignant transformation. Comparable changes in puberty onset, mammary gland morphology, and tumor incidence were observed in the offspring of rats treated daily with 20 ng of E2 during pregnancy. These data, if extrapolated to humans, may explain the link among diet, early puberty onset, mammary parenchymal patterns, and breast cancer risk, and indicate that an in utero exposure to a diet high in n - 6 PUFA and/or estrogenic stimuli may be critical for affecting breast cancer risk.

Intrauterine environment and breast cancer risk in women: a population-based study

BACKGROUND

The established risk factors for female breast cancer, including nulliparity, age at first birth, age at menarche, and age at menopause, do not adequately explain the occurrence pattern of this cancer. Therefore, additional factors need to be considered to advance our understanding of the causes of breast cancer. Evidence obtained from animals and humans indicates that the perinatal period may be particularly important. Our earlier studies, based on a subsample of the present investigation, suggested that factors thought to be positively associated with estrogen levels during pregnancy are positively associated with breast cancer risk. However, the associated confidence intervals (CIs) were generally wide, indicating considerable variability in the data.

PURPOSE

We studied a large number of incident breast cancer case patients and evaluated several perinatal variables in relation to breast cancer risk. These variables included some not previously studied, such as gestational age and neonatal jaundice. We also investigated twin membership as a predictor variable and death from breast cancer, in addition to occurrence of breast cancer, as an alternative outcome variable.

METHODS

Birth records for all deliveries at five different hospitals in Sweden during the period from 1874 through 1961 were used to define a large cohort of women. Incident case patients with breast cancer in this cohort were ascertained through the National Cancer Registry or the Uppsala Regional Cancer Registry from 1958 through 1994. In a case-control study nested in the cohort, we abstracted data from birth records on 1068 women with incident breast cancer and on 2727 control subjects individually matched to the case patients on date of birth. We modeled the data through conditional logistic regression. All P values were derived from two-sided statistical tests.

RESULTS

We found a markedly reduced risk for breast cancer in women whose mothers had pregnancy toxemia (odds ratio [OR] = 0.41; 95% CI = 0.22-0.79) and an excess risk on women who had neonatal jaundice (OR = 2.16; 95% CI = 1.27-3.67) or who were born before 33 weeks of gestation (OR = 3.96; 95% CI = 1.45-10.81). Compared with the risk for breast cancer in the singleton, the risk for breast cancer in dizygotic twins was increased, although this increase was not statistically significant (OR = 1.72; 95% CI = 0.92-3.20). There was no evidence in these data for a statistically significant or substantial association of breast cancer risk with birth size indicators (i.e., weight and length at birth and placental weight).

CONCLUSION AND IMPLICATIONS

Because pregnancy toxemia is associated with low levels of estrogens and neonatal jaundice, severe prematurity, and dizygotic twins with high levels of estrogens, our findings suggest that estrogens and other hormonal factors, known to influence breast cancer risk in the adult, may also play a critical role during the intrauterine period.

A population-based study of cancer risk in twins: relationships to birth order and sexes of the twin pair

One thousand and sixty-three twins with cancer whose co-twin was born alive were identified among patients born since September 1939 with cancers incident in England and Wales during 1971-1984 at childhood and young adult ages. Site-specific risks of cancer were analysed in relation to birth order within the twinship and sexes of the twin pair, using adjusted national birth data to give control distributions of these variables. Risk of leukaemia was increased in first-born twins, risk of testicular cancer was increased in second-born twins with female co-twins but decreased in second-born twins with male co-twins and lung cancer risk was increased in first-born twins with same-sex co-twins. Cutaneous melanoma risk was increased in persons with opposite-sex co-twins, nervous system cancer risk was increased in females with opposite-sex co-twins and Hodgkin's disease risk was increased in persons with same-sex co-twins. For most of the findings, no previous comparable analyses are available, so interpretation of the results must be provisional until the analyses can be repeated on other data. The result for leukaemia would accord with previous suggestions that leukaemia may be of prenatal origin and may sometimes lead to intrauterine death. The Hodgkin's disease result would fit with theories of an infectious aetiology, and this view is strengthened by reanalysis of previous data on paralytic poliomyelitis in twins, which show a pattern similar to that for the Hodgkin's disease patients. Cancer risk in relation to birth order and sex of twins can give novel, objective data relating to prenatal and infectious disease aetiology of cancers.

Prevalence of a history of testicular cancer in a cohort of elderly twins

Prior studies have suggested that the risk of testicular cancer among dizygotic twins may exceed that among monozygotic twins or the general population. Cryptorchidism is associated with testicular cancer and twinship, and therefore might potentially explain the findings of the prior studies. In 1993-1994, when they were 66 to 77 years of age, 14,326 twin individuals in the National Academy of Sciences-National Research Council Twin Registry were interviewed by telephone. A history of testicular cancer was reported by 5 (0.08%) of 5951 monozygotic twins and 11 (0.16%) of 6992 dizygotic twins. Follow-up interviews concerning testicular cancer risk factors and treatment were able to be administered to 4 of the monozygotic and 9 of the dizygotic twins reporting testicular cancer. A history of cryptorchidism was reported in the follow-up interview by only one dizygotic twin. Our data agree with the results of prior studies reporting a more frequent occurrence of testicular cancer among dizygotic than monozygotic twins. Although somewhat limited by small numbers, our study also suggests that the findings of increased testicular cancer in dizygotic twins are not explained simply by increased occurrence of cryptorchidism in twins.