IGF-I during primiparous pregnancy and maternal risk of breast cancer

The role of pregnancy, perinatal factors and hormones in maternal cancer risk: a review of the evidence

An understanding of the origin of cancer is critical for cancer prevention and treatment. Complex biological mechanisms promote carcinogenesis, and there is increasing evidence that pregnancy-related exposures influence foetal growth cell division and organ functioning and may have a long-lasting impact on health and disease susceptibility in the mothers and offspring. Nulliparity is an established risk factor for breast, ovarian, endometrial and possibly pancreatic cancer, whilst the risk of kidney cancer is elevated in parous compared with nulliparous women. For breast, endometrial and ovarian cancer, each pregnancy provides an additional risk reduction. The associations of parity with thyroid and colorectal cancers are uncertain. The timing of reproductive events is also recognized to be important. Older age at first birth is associated with an increased risk of breast cancer, and older age at last birth is associated with a reduced risk of endometrial cancer. The risks of breast and endometrial cancers increase with younger age at menarche and older age at menopause. The mechanisms, and hormone profiles, that underlie alterations in maternal cancer risk are not fully understood and may differ by malignancy. Linking health registries and pooling of data in the Nordic countries have provided opportunities to conduct epidemiologic research of pregnancy exposures and subsequent cancer. We review the maternal risk of several malignancies, including those with a well-known hormonal aetiology and those with less established relationships. The tendency for women to have fewer pregnancies and at later ages, together with the age-dependent increase in the incidence of most malignancies, is expected to affect the incidence of pregnancy-associated cancer.

Early pregnancy sex steroids during primiparous pregnancies and maternal breast cancer: a nested case-control study in the Northern Sweden Maternity Cohort

BACKGROUND

Pregnancy and parity are associated with subsequent breast cancer risk. Experimental and epidemiologic data suggest a role for pregnancy sex steroid hormones.

METHODS

We conducted a nested case-control study in the Northern Sweden Maternity Cohort (1975-2007). Eligible women had provided a blood sample in the first 20 weeks of gestation during a primiparous pregnancy leading to a term delivery. The current study includes 223 cases and 417 matched controls (matching factors: age at and date of blood collection). Estrogen receptor (ER) and progesterone receptor (PR) status was available for all cases; androgen receptor (AR) data were available for 41% of cases (n = 92). Sex steroids were quantified by high-performance liquid chromatography tandem mass spectrometry. Odds ratios (ORs) and 95% confidence intervals were estimated using conditional logistic regression.

RESULTS

Higher concentrations of circulating progesterone in early pregnancy were inversely associated with ER+/PR+ breast cancer risk (OR_log2: 0.64 (0.41-1.00)). Higher testosterone was positively associated with ER+/PR+ disease risk (OR_log2: 1.57 (1.13-2.18)). Early pregnancy estrogens were not associated with risk, except for relatively high estradiol in the context of low progesterone (split at median, relative to low concentrations of both; OR: 1.87 (1.11-3.16)). None of the investigated hormones were associated with ER-/PR- disease, or with AR+ or AR+/ER+/PR+ disease.

CONCLUSIONS

Consistent with experimental models, high progesterone in early pregnancy was associated with lower risk of ER+/PR+ breast cancer in the mother. High circulating testosterone in early pregnancy, which likely reflects nonpregnant premenopausal exposure, was associated with higher risk of ER+/PR+ disease.

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.

The protective effect of parity in hormone receptor-positive, Ki-67 expressing breast cancer

BACKGROUND

Epidemiologic studies showed that the experience of pregnancy is associated with a reduced risk of breast cancer. We hypothesized that parity may differentially be associated with the development of invasive breast cancer by each subtype.

METHODS

We reviewed the clinical, radiological, and pathological records of women diagnosed with invasive ductal carcinoma of the breast at Samsung Medical Center between 2005 and 2009. Clinicopathologic results were assessed by χ(2) and Fisher's exact tests with a Bonferroni correction for categorical variables, and by the Kruskal-Wallis test for nonparametric continuous variables. A multinomial logistic regression model was used for multivariate analysis.

RESULTS

Among a total of 3,095 patients, 283 (9.14 %) patients were nulliparous. Older age, higher pN, and expression of HER2 were associated with parity. In the analysis between parity and molecular subtypes, parity also had a variable influence on breast cancer subtypes (p = 0.032). Intergroup analysis with multiple comparison showed that luminal B subtype was related to nulliparity compared with HER2-positive subtypes (p = 0.03).

CONCLUSIONS

The effect of parity on the development of breast cancer differed by hormone receptor and HER2 expression. It seems that parity might have a protective effect against hormone receptor-positive breast cancer, especially cancers expressing HR+ and Ki-67. Further basic research to define and understand this result is ongoing.

Placental weight and breast cancer risk in young women: a registry-based cohort study from Norway

BACKGROUND

Pregnancy has a short-term risk-increasing effect on breast cancer that may be attributed to growth-promoting effects of pregnancy hormones on prevalent but undetected tumors. Results of two previous studies suggested that placental weight may be positively associated with breast cancer risk.

METHODS

In a cohort of 338,051 women followed from 1999 to 2008, on the basis of data linkage between the Medical Birth Registry of Norway and the Cancer Registry of Norway, we assessed whether placental weight in a woman's most recent pregnancy was related to breast cancer risk during the first years following pregnancy.

RESULTS

During follow-up (median, 6.0 years; interquartile range, 3.0-8.3 years), 648 women were diagnosed with breast cancer at a mean age of 38.4 years (standard deviation, 5.3 years). Placental weight in the most recent pregnancy was not associated with breast cancer risk: the hazard ratio per 100-gram increase in placental weight was 1.03 [95% confidence interval, 0.96-1.10]. There was a similar lack of association related to mean placental weight across pregnancies and to placental weight associated with the first birth.

CONCLUSION

We could not confirm previous reports that women who develop large placentas are at increased risk of breast cancer.

IMPACT

The epidemiologic support for an association of placental weight with breast cancer risk remains inconclusive. More research is needed to identify factors that influence breast cancer risk in young women.

Circulating insulin-like growth factor-I in pregnancy and maternal risk of breast cancer

BACKGROUND

Elevated serum concentrations of insulin-like growth factor (IGF)-I have been associated with increased risk of developing breast cancer. Previously, we reported a similar association in samples obtained during pregnancy. This study was conducted to further characterize the association of IGF-I during pregnancy with maternal breast cancer risk.

METHODS

A case-control study was nested within the Finnish Maternity Cohort. The study was limited to primiparous women younger than 40 years, who donated blood samples during early (median, 12 weeks) pregnancy and delivered a single child at term. Seven hundred nineteen women with invasive breast cancer were eligible. Two controls (n = 1,434) were matched with each case on age and date at blood donation. Serum IGF-I concentration was measured using an Immulite 2000 analyzer. Conditional logistic regression was used to estimate ORs and 95% CIs.

RESULTS

No significant associations were observed between serum IGF-I concentrations and breast cancer risk in both the overall analysis (OR, 1.08; 95% CI, 0.80-1.47) and in analyses stratified by histologic subtype, lag time to cancer diagnosis, age at pregnancy, or age at diagnosis.

CONCLUSION

There was no association between IGF-I and maternal breast cancer risk during early pregnancy in this large nested case-control study.

IMPACT

Serum IGF-I concentrations during early pregnancy may not be related to maternal risk of developing breast cancer.

Levels of insulin-like growth factor during pregnancy and maternal cancer risk: a nested case-control study

Previous studies have suggested that pregnancy measures of insulin-like growth factors (IGFs) may be related to breast cancer risk in mothers. IGFs may also be important in cervical cancer etiology. We conducted a nested case-control study (69 breast cancer cases, 151 cervical cancer cases, 443 controls) among mothers of the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort. Over 70% of blood samples was taken prior to 15 weeks' gestation; the remainder before 30 weeks. Logistic regression, controlling for maternal age, gestational age, and sample type (plasma/serum) was used to model the association between IGFs and maternal cancer risk. Neither IGF-I nor IGF-II were associated with breast or cervical cancer. IGF-binding protein (BP)-3 was not related to breast cancer, but there was a suggestion that women in the highest compared to lowest quartile of IGFBP-3 had reduced risk of cervical cancer, OR 0.43 (95% CI 0.21-0.86). In conclusion, the importance of IGFs measured in pregnancy and later breast and cervical cancer remains unclear, though IGFBP-3 may be a marker of lowered risk.

Maternal hormones during early pregnancy: a cross-sectional study

BACKGROUND

Little is known about correlates of first-trimester pregnancy hormones as in most studies maternal hormones have been measured later in gestation. We examined the associations of maternal characteristics and child sex with first-trimester maternal concentrations of four hormones implicated in breast cancer: human chorionic gonadotropin (hCG), alpha-fetoprotein (AFP), insulin-like growth factor (IGF)-I, and IGF-II.

METHODS

About 338 serum samples donated to the Northern Sweden Maternity Cohort (NSMC), 1975-2001, during the first trimester of uncomplicated pregnancies, were analyzed for the hormones of interest as a part of a case-control study. The associations of maternal characteristics and child sex with hormone concentrations were investigated by correlation, general linear regression, and multivariate regression models.

RESULTS

In the first trimester, greater maternal age was inversely correlated with IGF-I and IGF-II. In comparison with women carrying their first child, already parous women had higher IGF-I but lower hCG. Greater maternal weight and smoking were inversely correlated with hCG. No differences in hormone levels by child sex were observed.

CONCLUSIONS

Our analyses indicated that potentially modifiable maternal characteristics (maternal weight and smoking) influence first-trimester pregnancy maternal hormone concentrations.