Potential Mechanisms underlying the Protective Effect of Pregnancy against Breast Cancer: A Focus on the IGF Pathway

A first full-term birth at an early age protects women against breast cancer by reducing lifetime risk by up to 50%. The underlying mechanism resulting in this protective effect remains unclear, but many avenues have been investigated, including lobular differentiation, cell fate, and stromal composition. A single pregnancy at an early age protects women for 30-40 years, and this long-term protection is likely regulated by a relatively stable yet still modifiable method, such as epigenetic reprograming. Long-lasting epigenetic modifications have been shown to be induced by pregnancy and to target the IGF pathway. Understanding how an early first full-term pregnancy protects against breast cancer and the role of epigenetic reprograming of the IGF system may aid in developing new preventative strategies for young healthy women in the future.

Pregnancy-related characteristics and breast cancer risk

Breast tissues undergo extensive physiologic changes during pregnancy, which may affect breast carcinogenesis. Gestational hypertension, preeclampsia/eclampsia, gestational diabetes, pregnancy weight gain, and nausea and vomiting (N&V) during pregnancy may be indicative of altered hormonal and metabolic profiles and could impact breast cancer risk. Here, we examined associations between these characteristics of a woman's pregnancy and her subsequent breast cancer risk. Participants were parous women that were recruited to a population-based case-control study (Western New York Exposures and Breast Cancer Study). Cases (n = 960), aged 35-79 years, had incident, primary, histologically confirmed breast cancer. Controls (n = 1,852) were randomly selected from motor vehicle records (< 65 years) or Medicare rolls (≥ 65 years). Women were queried on their lifetime pregnancy experiences. Multivariable-adjusted logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). N&V during pregnancy was inversely associated with breast cancer risk. Relative to those who never experienced N&V, ever experiencing N&V was associated with decreased risk (OR 0.69, 95% CI 0.56-0.84) as were increased N&V severity (p trend < 0.001), longer duration (p trend < 0.01), and larger proportion of affected pregnancies (p trend < 0.0001) among women with ≥ 3 pregnancies. Associations were stronger for more recent pregnancies (< 5 years). Findings did not differ by menopausal status or breast cancer subtype including estrogen receptor and HER2 expression status. Other pregnancy characteristics examined were not associated with risk. We observed strong inverse associations between pregnancy N&V and breast cancer risk. Replication of these findings and exploration of underlying mechanisms could provide important insight into breast cancer etiology and prevention.

Maternal serum insulin-like growth factor-I at 11-13 weeks in preeclampsia

OBJECTIVE

To investigate the maternal serum concentration of insulin-like growth factor-I (IGF-I) in the first trimester of pregnancies that subsequently develop preeclampsia (PE) and to examine the possible association with uterine artery pulsatility index (PI).

METHODS

The maternal serum concentration of IGF-I and uterine artery PI at 11-13 weeks were measured in 53 cases that developed PE, including 18 that required delivery before 34 weeks (early-PE) and 106 unaffected controls. The measured IGF-I concentration and uterine artery PI were converted into a multiple of the expected median (MoM) in unaffected pregnancies, and median MoM values were compared in the outcome groups. The significance of association of IGF-I MoM with uterine artery PI MoM was determined by regression analysis.

RESULTS

In the early-PE and late-PE groups, compared to the unaffected controls, the median IGF-I decreased (0.53 and 0.55 MoM, respectively) and uterine artery PI increased (1.55 and 1.21 MoM, respectively). In the group that developed PE, there was no significant association between serum IGF-I and uterine artery PI (p = 0.632).

CONCLUSION

In pregnancies destined to develop PE, the circulating levels of IGF-I decrease from the first trimester of pregnancy suggesting that IGF-I may be implicated in the pathogenesis of the disease.

Placental expression of insulin-like growth factor-I, fibroblast growth factor-basic, and neural cell adhesion molecule in preeclampsia

OBJECTIVE

To investigate placental expression of insulin-like growth factor-I (IGF-I), fibroblast growth factor-basic (FGF-b), and neural cell adhesion molecule (N-CAM) in preeclampsia.

STUDY DESIGN

An immunohistochemical analysis using IGF-I, FGF-b, and N-CAM antibodies was conducted on 4% paraformaldehyde-fixed placental tissues of preeclamptic patients (N = 14) and normotensive pregnant subjects (N = 10). Immunostaining patterns of chorionic villi and amniochorionic membranes were assessed.

RESULTS

Significantly increased FGF-b and N-CAM immunoreactivities in cytotrophoblasts and increased FGF-b immunoreactivity in capillary endothelium of chorionic villi of preeclamptic subjects were noted. Significantly increased FGF-b and decreased N-CAM immunoreactivities in extravillous trophoblasts and decidual cells of amniochorionic membranes obtained from preeclamptic subjects were demonstrated. Additionally, a significantly increased IGF-I immunoreactivity was shown in decidual cells of preeclamptic cases.

CONCLUSION

Investigation of the regional distribution of IGF-I, FGF-b, and N-CAM at the maternal-fetal interface establishes a better understanding of cell-specific altered growth processes, which may be associated with the pathogenesis of preeclampsia.

Prediction of pregnancy complications by first-trimester maternal serum PAPP-A and free beta-hCG and with second-trimester uterine artery Doppler

BACKGROUND

Previous studies have shown an association between low first trimester maternal serum free beta-hCG and PAPP-A and subsequent development of pregnancy complications. Similarly, uterine artery Doppler in the late second trimester has shown that high impedance to flow is associated with increased risk for preeclampsia and fetal growth restriction. The objective of this study is to determine whether there is an association between the maternal serum concentration of PAPP-A and free beta-hCG at 11-13(+6) weeks with the uterine artery pulsatility index (PI) at 22-24 weeks, and secondly, to compare the screening characteristics of the two methods in the prediction of adverse pregnancy outcome.

METHODS

Maternal serum PAPP-A and free beta-hCG at 11-13(+6) weeks and uterine artery PI at 22-24 weeks were measured in 4390 women with singleton pregnancies. Pregnancies with chromosomal defects or fetal anomalies were excluded. The biochemical and Doppler measurements were compared between those with normal outcome and those resulting in spontaneous preterm delivery, pre-eclampsia and fetal growth restriction (FGR). Detection rates using a combination of the biochemical and Doppler measurements were investigated.

RESULTS

In the pregnancies resulting in pre-eclampsia (n = 64) and FGR (n = 172), the median PAPP-A was lower (0.844 and 0.813 MoM), the median uterine artery mean PI was higher (1.56 and 1.18) but the median free betahCG was not significantly different (0.923 and 0.933 MoM) than in the normal outcome group. In the preterm delivery group (n = 159), the median free beta-hCG (0.944 MoM) and uterine artery mean PI (1.06) were not significantly different from normal but the median PAPP-A (0.928 MoM) was significantly lower than normal. In screening for pre-eclampsia, the detection rate, for a 5% false-positive rate, was 14.1% for PAPP-A, 54.7% for uterine artery mean PI and 62.1% for a combination of PAPP-A and uterine artery mean PI.

CONCLUSION

Maternal serum PAPP-A at 11-13(+6) of gestation is significantly lower in adverse pregnancy outcomes. The combination of first trimester serum PAPP-A and uterine artery mean PI at 22-24 weeks improves the screening efficacy for the prediction of pre-eclampsia.

Altered metabolic profiles among older mothers with a history of preeclampsia

Preeclampsia has been linked to increased risk for cardiovascular disease and, more recently, to reduced risk for breast cancer later in life. The altered chronic disease risk associated with prior preeclampsia may reflect underlying metabolic differences. In this case-control study, we examined the metabolic profiles of older mothers with and without a history of preeclampsia in their first pregnancies. At the time of the study, subjects were non-pregnant, non-smoking women who completed their first pregnancies at age 30 or older, were pre-menopausal, and were free of serious chronic disease. Cases were 13 women who experienced preeclampsia in their first pregnancies; controls were 13 women with uncomplicated first pregnancies, frequency matched to cases on race/ethnicity, current age, and age at delivery. A fasting blood sample was collected from each subject during the luteal phase (day 19-22) of the menstrual cycle and assayed for specific factors thought to be linked to hypertensive disease or breast cancer. Compared to women with uncomplicated pregnancies, those with a history of preeclampsia had significantly elevated levels of fasting serum triglycerides, insulin and glucose, and a higher fasting insulin resistance index, suggesting that women with prior preeclampsia were relatively insulin resistant. In addition, cases had higher levels of insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) and a higher molar ratio of IGFBP-3 to IGF-1 than did controls. Adjustment for obesity and other potential confounders did not appreciably alter the magnitude of these associations. This preliminary study suggests that women with a history of preeclampsia have persistent metabolic abnormalities consistent with their observed excess risk for cardiovascular morbidity and mortality, and their apparent reduced risk for breast cancer later in life.