Pregnancy protection of breast cancer: new insights reveal unanswered questions

Pregnancy reprograms the epigenome of mammary epithelial cells and blocks the development of premalignant lesions

Pregnancy causes a series of cellular and molecular changes in mammary epithelial cells (MECs) of female adults. In addition, pregnancy can also modify the predisposition of rodent and human MECs to initiate oncogenesis. Here, we investigate how pregnancy reprograms enhancer chromatin in the mammary epithelium of mice and influences the transcriptional output of the oncogenic transcription factor cMYC. We find that pregnancy induces an expansion of the active cis-regulatory landscape of MECs, which influences the activation of pregnancy-related programs during re-exposure to pregnancy hormones in vivo and in vitro. Using inducible cMYC overexpression, we demonstrate that post-pregnancy MECs are resistant to the downstream molecular programs induced by cMYC, a response that blunts carcinoma initiation, but does not perturb the normal pregnancy-induced epigenomic landscape. cMYC overexpression drives post-pregnancy MECs into a senescence-like state, and perturbations of this state increase malignant phenotypic changes. Taken together, our findings provide further insight into the cell-autonomous signals in post-pregnancy MECs that underpin the regulation of gene expression, cellular activation, and resistance to malignant development.

Mammary epithelial cells are epigenetically modified during pregnancy, these changes can influence the pre-disposition to cancer. Here, the authors examine the epigenetic landscape of mammary epithelial cells pre and post pregnancy and identify changes to the epigenetic landscape, which can protect mice from Myc induced cancer.

Alcohol consumption and mammographic density in the Danish Diet, Cancer and Health cohort

PURPOSE

We examined the association between alcohol consumption and mammographic density (MD) considering in detail the time of exposure and the type of alcohol.

METHODS

Of 5,356 women (4,489 post-menopausal) from the Danish Diet, Cancer and Health cohort (1993-1997) who attended mammographic screening in Copenhagen (1993-2001), we used MD (mixed/dense or fatty) assessed at the first screening after cohort entry. Alcohol consumption was assessed at the time of recruitment. Logistic regression was used to estimate associations [odds ratios (OR), 95% confidence intervals (CI)] between alcohol consumption and MD.

RESULTS

The mean age was 56.2 years, 56.5% of women had mixed/dense MD, and 91.8% were alcohol consumers. There was no association between current alcohol consumption and MD at baseline (age 50-65, on average 1 year before MD assessment) neither between age at drinking initiation and MD, in the fully adjusted model. There was a borderline statistically significantly increased OR of having mixed/dense MD in women who consumed > 7 drinks/week at age 20-29 (1.31, 95% CI 1.00-1.72) compared to non-drinkers in this age group, and no effect of drinking at age 30-39, 40-49 or after > 50 years, when adjusting for current drinking. However, when considering different types of alcohol, drinking spirits at age 20-29 was positively associated with mixed/dense breast (3-7 drinks/week: OR 1.74, 95% CI 1.12-2.72); >7 drinks/week: (OR 1.76, 95% CI 0.73-4.23). No consistent pattern was found with beer, wine, or fortified wine.

CONCLUSIONS

We found higher MD among women with high alcohol consumption in early adulthood (ages 20-29), in those drinking spirits.

Physical activity from menarche to first pregnancy and risk of breast cancer

Breast tissue is particularly susceptible to exposures between menarche and first pregnancy, and a longer interval between these reproductive events is associated with elevated breast cancer risk. Physical activity during this time period may offset breast cancer risk, particularly for those at highest risk with longer menarche-to-first-pregnancy intervals. We used data from 65,576 parous women in the Nurses' Health Study II free of cancer in 1989 (baseline) and recalled their leisure-time physical activity at ages 12-34 in 1997. Current activity was collected at baseline and over follow-up. Relative risks (RRs) were estimated using multivariable Cox proportional hazards regression models. Between 1989 and 2011, 2,069 invasive breast cancer cases were identified. Total recreational activity between menarche and first pregnancy was not significantly associated with the risk of breast cancer. However, physical activity between menarche and first pregnancy was associated with significantly lower breast cancer risk among women in the highest category of a menarche-to first-pregnancy interval (≥20 years; RR for the highest versus the lowest quartile = 0.73, 95% confidence interval = 0.55-0.97; Ptrend  = 0.045; Pinteraction  = 0.048). This was not observed in women with a shorter interval. Physical activity between menarche and first pregnancy was associated with a lower risk of breast cancer among women with at least 20 years between these reproductive events. This may provide a modifiable factor that women can intervene on to mitigate their breast cancer risk associated with a longer interval.

Is breast cancer risk associated with alcohol intake before first full-term pregnancy?

PURPOSE

It is plausible that breast tissue is particularly susceptible to carcinogens, including ethanol, between menarche and the first full-term pregnancy ("first pregnancy"). There is some epidemiological evidence that intake before the first pregnancy is more closely associated with risk of breast cancer than is intake thereafter. We examined this association using lifetime alcohol consumption data from a prospective cohort study.

METHODS

We calculated usual alcohol intake for age periods 15-19 years and for 10-year period from age 20 to current age (in grams per day) using recalled frequency and quantity of beverage-specific consumption for 13,630 parous women who had their first pregnancy at age 20 years or later, had no cancer history and were aged 40-69 years at enrollment. Cox regression was performed to estimate hazard ratios (HRs) and their 95 % confidence intervals (CIs).

RESULTS

A total of 651 incident invasive adenocarcinomas of the breast were diagnosed during a mean follow-up of 16.1 years. Alcohol consumption was low overall with only a few drinking ≥40 g/day. Intake before the first pregnancy was markedly lower (mean intake: 2.5 g/day; abstention: 58.8 %) than intake thereafter (mean intake: 6.0 g/day; abstention: 33.6 %). Any alcohol intake before the first pregnancy was associated with an increased risk of breast cancer (HR 1.35, 95 % CI 1.10-1.66 for drinking compared with abstention), whereas any intake after the first pregnancy was not (HR 0.89, 95 % CI 0.72-1.09).

CONCLUSIONS

Limiting alcohol intake before the first pregnancy might reduce women's risk of breast cancer.

Links between alcohol consumption and breast cancer: a look at the evidence

Alcohol consumption by adult women is consistently associated with risk of breast cancer. Several questions regarding alcohol and breast cancer need to be addressed. Menarche to first pregnancy represents a window of time when breast tissue is particularly susceptible to carcinogens. Youth alcohol consumption is common in the USA, largely in the form of binge drinking and heavy drinking. Whether alcohol intake acts early in the process of breast tumorigenesis is unclear. This review aims to focus on the influences of timing and patterns of alcohol consumption and the effect of alcohol on intermediate risk markers. We also review possible mechanisms underlying the alcohol-breast cancer association.

Breast cancer risk accumulation starts early: prevention must also

Nearly one in four breast cancers is diagnosed before the age of 50, and many early-stage premalignant lesions are present but not yet diagnosed. Therefore, we review evidence to support the strategy that breast cancer prevention efforts must begin early in life. This study follows the literature review methods and format. Exposures during childhood and adolescence affect a woman's long-term risk of breast cancer, but have received far less research attention than exposures that occur later in life. Breast tissue undergoes rapid cellular proliferation between menarche and first full-term pregnancy, and risk accumulates rapidly until the terminal differentiation that accompanies first pregnancy. Evidence on childhood diet and growth in height, and adolescent alcohol intake, among other adolescent factors is related to breast cancer risk and risk of premalignant proliferative benign lesions. Breast cancer prevention efforts will have the greatest effect when initiated at an early age and continued over a lifetime. Gaps in knowledge are identified and deserve increase attention to inform prevention.

Adolescent dietary fiber, vegetable fat, vegetable protein, and nut intakes and breast cancer risk

The importance of early-life exposures in breast cancer development is increasingly recognized. However, limited research has evaluated the relationship between adolescent diet and subsequent risk of breast cancer and reported inconsistent results. This population-based case-control study investigated the associations of dietary fiber, vegetable protein, vegetable fat, and nuts consumed during adolescence with adult breast cancer risk. Women, ages 25-74 years, who were diagnosed with first primary breast cancer between 2002 and 2003, were identified using the Ontario Cancer Registry. Controls were identified through random-digit dialing and age-frequency matched to cases. Diet at ages 10-15 was assessed with a 55-item food frequency questionnaire among 2,865 cases and 3,299 controls. Logistic regression was performed to estimate odds ratios (ORs) and 95 % confidence intervals (CIs). Inverse associations were found between intakes of dietary fiber, vegetable protein, vegetable fat, and nuts during adolescence and breast cancer risk, which persisted after controlling for adult intakes. The ORs (95 % CI) for the highest versus the lowest quintile of intake were 0.66 (0.55-0.78; P trend < 0.0001) for fiber, 0.80 (0.68-0.95; P trend = 0.01) for vegetable protein, 0.74 (0.63-0.87; P trend = 0.002) for vegetable fat, and 0.76 (0.61-0.95 for ≥1 serving/day vs. <1 serving/month intake; P trend = 0.04) for nuts. The reduced risk for adolescent intakes of fiber, vegetable protein, and nuts was largely limited to postmenopausal women (P interaction ≤ 0.05). Dietary fiber, vegetable protein, vegetable fat, and nuts consumed during adolescence were associated with reduced breast cancer risk.

Adolescent dietary fiber, vegetable fat, vegetable protein, and nut intakes and breast cancer risk

The importance of early-life exposures in breast cancer development is increasingly recognized. However, limited research has evaluated the relationship between adolescent diet and subsequent risk of breast cancer and reported inconsistent results. This population-based case-control study investigated the associations of dietary fiber, vegetable protein, vegetable fat, and nuts consumed during adolescence with adult breast cancer risk. Women, ages 25-74 years, who were diagnosed with first primary breast cancer between 2002 and 2003, were identified using the Ontario Cancer Registry. Controls were identified through random-digit dialing and age-frequency matched to cases. Diet at ages 10-15 was assessed with a 55-item food frequency questionnaire among 2,865 cases and 3,299 controls. Logistic regression was performed to estimate odds ratios (ORs) and 95 % confidence intervals (CIs). Inverse associations were found between intakes of dietary fiber, vegetable protein, vegetable fat, and nuts during adolescence and breast cancer risk, which persisted after controlling for adult intakes. The ORs (95 % CI) for the highest versus the lowest quintile of intake were 0.66 (0.55-0.78; P trend < 0.0001) for fiber, 0.80 (0.68-0.95; P trend = 0.01) for vegetable protein, 0.74 (0.63-0.87; P trend = 0.002) for vegetable fat, and 0.76 (0.61-0.95 for ≥1 serving/day vs. <1 serving/month intake; P trend = 0.04) for nuts. The reduced risk for adolescent intakes of fiber, vegetable protein, and nuts was largely limited to postmenopausal women (P interaction ≤ 0.05). Dietary fiber, vegetable protein, vegetable fat, and nuts consumed during adolescence were associated with reduced breast cancer risk.

Alcohol intake between menarche and first pregnancy: a prospective study of breast cancer risk

BACKGROUND

Adult alcohol consumption during the previous year is related to breast cancer risk. Breast tissue is particularly susceptible to carcinogens between menarche and first full-term pregnancy. No study has characterized the contribution of alcohol consumption during this interval to risks of proliferative benign breast disease (BBD) and breast cancer.

METHODS

We used data from 91,005 parous women in the Nurses' Health Study II who had no cancer history, completed questions on early alcohol consumption in 1989, and were followed through June 30, 2009, to analyze breast cancer risk. A subset of 60,093 women who had no history of BBD or cancer in 1991 and were followed through June 30, 2001, were included in the analysis of proliferative BBD. Relative risks (RRs) were estimated using Cox proportional hazard regression.

RESULTS

We identified 1609 breast cancer cases and 970 proliferative BBD cases confirmed by central histology review. Alcohol consumption between menarche and first pregnancy, adjusted for drinking after first pregnancy, was associated with risks of breast cancer (RR = 1.11 per 10 g/day intake; 95% confidence interval [CI] = 1.00 to 1.23) and proliferative BBD (RR = 1.16 per 10 g/day intake; 95% CI = 1.02 to 1.32). Drinking after first pregnancy had a similar risk for breast cancer (RR = 1.09 per 10 g/day intake; 95% CI = 0.96 to 1.23) but not for BBD. The association between drinking before first pregnancy and breast neoplasia appeared to be stronger with longer menarche to first pregnancy intervals.

CONCLUSIONS

Alcohol consumption before first pregnancy was consistently associated with increased risks of proliferative BBD and breast cancer.