Gender of offspring and maternal breast cancer risk

Cancer Susceptibility as a Cost of Reproduction and Contributor to Life History Evolution

Reproduction is one of the most energetically demanding life-history stages. As a result, breeding individuals often experience trade-offs, where energy is diverted away from maintenance (cell repair, immune function) toward reproduction. While it is increasingly acknowledged that oncogenic processes are omnipresent, evolving and opportunistic entities in the bodies of metazoans, the associations among reproductive activities, energy expenditure, and the dynamics of malignant cells have rarely been studied. Here, we review the diverse ways in which age-specific reproductive performance (e.g., reproductive aging patterns) and cancer risks throughout the life course may be linked via trade-offs or other mechanisms, as well as discuss situations where trade-offs may not exist. We argue that the interactions between host–oncogenic processes should play a significant role in life-history theory, and suggest some avenues for future research.

Pregnancy characteristics and maternal breast cancer risk: a review of the epidemiologic literature

The short- and long-term effects of pregnancy on breast cancer risk are well documented. Insight into potential biological mechanisms for these associations may be gained by studying breast cancer risk and pregnancy characteristics (e.g., preeclampsia, twining), which may reflect hormone levels during pregnancy. To date, no review has synthesized the published literature for pregnancy characteristics and maternal breast cancer using systematic search methods. We conducted a systematic search to identify all published studies. Using PUBMED (to 31 July 2009), 42 relevant articles were identified. Several studies suggest that multiple births may be associated with a lowered breast cancer risk of about 10-30%, but results were inconsistent across 18 studies. The majority of 13 studies suggest about a 20-30% reduction in risk with preeclampsia and/or gestational hypertension. Six of seven studies reported no association for infant sex and breast cancer risk. Data are sparse and conflicting for other pregnancy characteristics such as gestational age, fetal growth, pregnancy weight gain, gestational diabetes, and placental abnormalities. The most consistent findings in a generally sparse literature are that multiple births and preeclampsia may modestly reduce breast cancer risk. Additional research is needed to elucidate associations between pregnancy characteristics, related hormonal profiles, and breast cancer risk.

Do placental genes affect maternal breast cancer? Association between offspring's CGB5 and CSH1 gene variants and maternal breast cancer risk

The protective effect of full-term pregnancy against breast cancer is thought to be induced by two placental hormones: human chorionic gonadotropin and human chorionic somatotropin hormone (CSH) produced by the placental trophoblastic cells. We hypothesized that variants in placental genes encoding these hormones may alter maternal breast cancer risk subsequent to pregnancy. We conducted a case-control study to examine the association between polymorphisms in a woman's placental (i.e., her offspring's) homologous chorionic gonadotrophin beta5 (CGB5) and CSH1 genes and her post-pregnancy breast cancer risk. A total of 293 breast cancer cases and 240 controls with at least one offspring with available DNA were selected from the New York site of the Breast Cancer Family Registry. Three single nucleotide polymorphisms (SNP) in CGB5 and CSH1 genes were genotyped for 844 offspring of the cases and controls. Overall, maternal breast cancer risk did not significantly differ by the offspring's carrier status of the three SNPs. Among women with an earlier age at childbirth (younger than the median age of 26 years), those with a child carrying the variant C allele of CGB5 rs726002 SNP had an elevated breast cancer risk [odds ratio (OR), 2.09; 95% confidence interval (95% CI), 1.17-3.73]. Among women with a later age at childbirth, breast cancer risk did not differ by offspring's carrier status of CGB5 rs726002 SNP (OR, 0.90; 95% CI, 0.53-1.51; P for interaction=0.04). The findings suggest that placental CGB5 genotype may be predictive of maternal post-pregnancy breast cancer risk among women who give birth early in life.

Preeclampsia and maternal breast cancer risk by offspring gender: do elevated androgen concentrations play a role?

Among older mothers, preeclampsia in the first pregnancy was associated with a reduction in maternal breast cancer risk that was significantly more pronounced in women bearing male than female infants. Androgen concentrations in male, preeclamptic pregnancies were consistent with the hypothesis that elevated pregnancy androgens might mediate this apparent modifying effect of fetal gender.

Gender of offspring and maternal ovarian cancer risk

OBJECTIVE

A single live birth compared to nulliparity significantly reduces the risk for ovarian cancer, but exactly how pregnancy reduces ovarian cancer risk is unknown. We sought to determine whether offspring gender, which differentially alters maternal hormonal milieu, may be associated with maternal ovarian cancer risk.

METHODS

Parous women (n = 511) with incident ovarian cancer were compared to parous community controls (n = 1136) participating in a population-based case-control study of ovarian cancer (Delaware Valley, 1994-1998). In subgroup specific models for women with one, two, or three births, multivariate logistic regression was used to assess the relationship between ovarian cancer and offspring gender, adjusting for age, race, education, oral contraceptives, breast feeding, tubal ligation, and ovarian cancer family history.

RESULTS

Compared to having all girls, women with all boys tended to have a reduced risk of ovarian cancer (OR = 0.80 95% CI: 0.58, 1.10), while women with boys and girls conferred the greatest protection (OR = 0.58, 95% CI: 0.43, 0.79). Among women with two births, the association was observed for those with one boy and one girl (OR = 0.63, 95% CI: 0.40, 1.00), but not for those with two male offspring (OR = 1.12, 95% CI: 0.68, 1.85). This result was consistent among women with three births (OR = 0.42, 95% CI: 0.21, 0.84; OR = 0.47, 95% CI: 0.23, 0.95; OR = 0.49, 95% CI: 0.20, 1.21; for one, two, and three boys, respectively, compared to all girls).

CONCLUSION

Compared to having all girls, bearing both male and female offspring may be associated with a decrease in maternal ovarian cancer risk, although the biologic relevance of this observation is unclear.

The impact of a reduced fertility rate on women's health

HEALTH ISSUE: Total fertility rates (TFRs) have decreased worldwide. The Canadian fertility rate has gone from 3.90 per woman in 1960 to 1.49 in 2000. However, not many studies have examined the impact on women's health of reduced fertility rates, delayed fertility and more births to unmarried women. This paper presents information on the relation between family size and specific determinants of health. KEY FINDINGS: The rate of TFR decline varies considerably by geographic location and socio-demographic subgroup. Further, the associations between family size and selected determinants of health are different for women and men. For example a woman with one child is almost four times more likely to be "coupled" than a childless woman, and if she has two children she is significantly more likely to be "coupled" than if she had only one child. However, a man with one or more children is over six times more likely to be "coupled" than his childless counterpart, and this does not vary with family size. DATA GAPS AND RECOMMENDATIONS: There is a paucity of data on the impact of reduced fertility rates on women's health in general and on how women's roles affect their decision to have children. While it would be useful to examine longer-term health outcomes by parity and age of first birth, as well as socio-economic and role-related variables these longitudinal and detailed "role related" data are not available. Given the differing profiles of women and men with children, further health policies research is needed to support vulnerable women with children.

A prospective study on the possible association between having children and colon cancer risk: findings from the JACC Study

If having children is regarded as an exposure in life, its effect on a host could be considered as being due to female sex hormones associated with pregnancy in women and some lifestyle factors associated with large families in both men and women. To explore the roles of having children in the etiology of colon cancer, we examined 36,629 women and 24,877 men aged 40-79 years who completed a questionnaire on the number of children and other lifestyle factors from 1988 to 1990 in the Japan Collaborative Cohort Study for Evaluation of Cancer Risk. During 291,080 and 200,648 person-years of follow-up, we documented 198 female and 202 male incident colon cancers, respectively. After adjusting for some factors known or suspected to modify the risk of colon cancer, compared with the women with no children, the multivariate-adjusted relative risks of colon cancer were 0.74 (95% confidence interval [CI]: 0.30-1.84) for one child, 1.00 (95% CI: 0.46-2.20) for two, 0.70 (95% CI: 0.31-1.55) for three, and 0.59 (95% CI: 0.26-1.33) for four or more. The risk of colon cancer showed a significantly monotonic decrease with increasing number of children (P value for trend = 0.047). There was no association between the number of children and colon cancer risk among men. From these prospective data, having children may reduce risk of colon cancer among women, but not among men, suggesting that modifications of hormone profiles secondary to pregnancies may influence female colon cancer risk.

Placental genes and breast cancer: can the offspring's or father's genotypes predict mother's risk?

Half of the placental genes to which a woman is exposed during pregnancy come from her mating partner. Placental hormones, especially human chorionic gonadotropin and human placental lactogen, are considered to mediate the protective effects of full-term pregnancy and lactation on breast cancer risk. In this paper, variants in a woman's placental human chorionic gonadotropin or human placental lactogen genes, which are easily measurable through her offspring's genotypes, are associated with her breast cancer risk. If this hypothesis is true it would indicate that genotype of a woman's mating partner can affect her breast cancer risk and that offspring's genotype may be useful in predicting such risk. Because the placenta produces a wide range of hormones and enzymes (in addition to human chorionic gonadotropin and human placental lactogen), results supporting this hypothesis could open new dimensions to genetic research for diseases beyond breast cancer (including gynecologic tumors and reproductive and pregnancy-related disorders).

Ethnic differences in breast cancer risk: a possible role for pregnancy levels of alpha-fetoprotein?

BACKGROUND

Breast cancer incidence rates are up to five times higher in white women in the United States compared with Asian women in China and Japan. A search for factors that modify estrogen's biological effect differentially between ethnic groups may add to the understanding of international variations in breast cancer risk. Recent evidence indicates that alpha-fetoprotein, a glycoprotein produced by the fetal liver, has important antiestrogenic properties. During pregnancy, alpha-fetoprotein reaches peak concentrations in maternal serum during the third trimester.

METHODS

We compared pregnancy levels of alpha-fetoprotein in a population with high risk of breast cancer (Boston, MA) and low risk (Shanghai, China). Blood samples were collected around the 16th week and around the 27th week of gestation among women enrolled from March 1994 to October 1995. The number of specimens available for alpha-fetoprotein analysis was 1,033.

RESULTS

Alpha-fetoprotein levels, adjusted for gestational length, were substantially higher in Shanghai compared with Boston women at both time points. When adjustments were made for prepregnancy weight, parity, offspring's sex and maternal age, alpha-fetoprotein levels remained 13% higher in Shanghai at 16 weeks of pregnancy but not at 27 weeks.

CONCLUSIONS

These findings may explain, at least in part, the difference in breast cancer risk between Chinese and American women. On the population level, alpha-fetoprotein may influence risk by modifying the effect of biologically active estrogens both in the mother and in female offspring.

Hyperemesis gravidarum and subsequent breast cancer risk

Both parity and a young age at first pregnancy are associated with a reduction in breast cancer risk. The hormones involved in this process are not fully investigated. Human chorionic gonadotropin is a placental hormone, which in rats and in human breast cells in vitro has been shown to prevent against breast cancer. Hyperemesis, a severe nausea combined with vomiting during pregnancy, is associated with increased levels of human chorionic gonadotropin. We investigated the possible relationship between hyperemesis and subsequent breast cancer risk in a case-control study based on registry data. Among 13 079 breast cancer cases and 34 348 individually matched controls we found 148 cases and 405 controls who had been hospitalised for hyperemesis. Hyperemesis was not associated with breast cancer risk (adjusted odds ratio 1.05, 95% confidence interval 0.86-1.27), and similar risks were observed regardless of age at diagnosis, number of hospitalisations for hyperemesis or time of follow-up. Our results do not support the hypothesis that human chorionic gonadotropin is responsible for the protective effect of pregnancies upon breast cancer risk.

Latent-TGF-beta: an overview

The latency associated with the transforming growth factor-betas (TGF-betas) was discovered in 1984. Since the two publications on this subject in that year, there has been on average over sixty reports in which latency was the dominant theme for each of the past 10 years, proof enough of the interest in this field of growth factor research. As the mature 25 kD forms of the TGF-betas are required for them to exert their many, diverse biological effects, it was inevitable that an explanation of the structure and of the activation of the latent complexes be sought. This overview provides a description of these essential points. Now that it has been clearly shown that dysregulation of particular components of the TGF-beta signalling pathway is implicated in many human diseases, the activation of the latent TGF-beta complexes has taken on added importance. Technical improvements enable the distinction of active and latent TGF-beta proteins in vivo and have started to reveal anomalies in the control of activation in relation to various pathological situations.

Breast cancer risk in women who have had children with different partners

The fetal antigen hypothesis suggests that the lowered risk of breast cancer in parous women may be afforded by the development of antibodies to fetal antigens that are structurally similar to mammary cancer antigens. It has previously been hypothesized that the likelihood of developing such antibodies may be higher among women who have had children with more than 1 partner. Utilizing information on parenthood and breast cancer available in nationwide Swedish registers, we undertook a case-control study nested within a nation-wide cohort to address this issue. Number of partners fathering a child was categorized as 1, 2 and 3 or more. All analyses were restricted to subjects with 2 or more births and encompassed a total of 20,881 women with breast cancer and 111,989 control women. In an unadjusted analysis, the risk of breast cancer was somewhat lower (odds ratio [OR] = 0.94, 95% confidence interval [CI] 0.89-0.99) in women who had had children with 2 different partners compared with women who had had children conceived with the same partner. After adjustment for parity, age at first birth and educational level, however, the risk of breast cancer was slightly elevated (OR = 1.09, 95% CI: 1.03-1.15). Among women who had had children with 3 or more different men, the pattern was similar. The present results provide no support for the hypothesis that greater antigenic exposure afforded by having children with more than 1 man may reduce the risk of breast cancer. It remains possible, however, that pregnancy may influence breast cancer risk through some immunologic mechanism; further testing of the fetal antigen hypothesis may require development of relevant laboratory measures.