Objective: Breast-feeding is associated with positive maternal and infant health and development outcomes. To assist identifying women less likely to meet infant nutritional guidelines, we investigated the role of socio-economic position and parity on initiation of and sustaining breast-feeding for at least 6 months.Design: Prospective cohort study.Setting: Australia.Subjects: Parous women from the Australian Longitudinal Study on Women’s Health (born 1973–78), with self-reported reproductive and breast-feeding history (N4777).Results: While 89 % of women (83 % of infants) had ever breast-fed, only 60 % of infants were breast-fed for at least 6 months. Multiparous women were more likely to breast-feed their first child (~90 %v. ~71 % of primiparous women), and women who breast-fed their first child were more likely to breast-feed subsequent children. Women with a low education (adjusted OR (95 % CI): 2·09 (1·67, 2·62)) or a very low-educated parent (1·47 (1·16, 1·88)) had increased odds of not initiating breast-feeding with their first or subsequent children. While fewer women initiated breast-feeding with their youngest child, this was most pronounced among high-educated women. While ~60 % of women breast-fed their first, second and third child for at least 6 months, low-educated women (first child, adjusted OR (95 % CI): 2·19 (1·79, 2·68)) and women with a very low (1·82 (1·49, 2·22)) or low-educated parent (1·69 (1·33, 2·14)) had increased odds of not breast-feeding for at least 6 months.Conclusions: A greater understanding of barriers to initiating and sustaining breast-feeding, some of which are socio-economic-specific, may assist in reducing inequalities in infant breast-feeding.

Breast cancer is a common disease with a relatively good prognosis. Therefore, understanding the spectrum of diseases and mortality among breast cancer patients is important, though currently incomplete. We systematically examined the incidence and mortality of all diseases following a breast cancer diagnosis, as well as the sequential association of disease occurrences (trajectories). In this national cohort study, 57,501 breast cancer patients (2001–2011) were compared to 564,703 matched women from the general Swedish population and followed until 2012. The matching criteria included year of birth, county of residence, and socioeconomic status. Based on information from the Swedish Patient and Cause of Death Registries, hazard ratios (HR) were estimated for disease incidence and mortality. Conditional logistic regression models were used to identify disease trajectories among breast cancer patients. Among 225 diseases, 45 had HRs > 1.5 and p < 0.0002 when comparing breast cancer patients with the general population. Diseases with highest HRs included lymphedema, radiodermatitis, and neutropenia, which are side effects of surgery, radiotherapy, and chemotherapy. Other than breast cancer, the only significantly increased cause of death was other solid cancers (HR = 1.16, 95% CI = 1.08–1.24). Two main groups of disease trajectories were identified, which suggest menopausal disorders as indicators for other solid cancers, and both neutropenia and dorsalgia as diseases and symptoms preceding death due to breast cancer. While an increased incidence of other diseases was found among breast cancer patients, increased mortality was only due to other solid cancers. Preventing death due to breast cancer should be a priority to prolong life in breast cancer patients, but closer surveillance of other solid cancers is also needed.

Mammographic features influence breast cancer risk and are used in risk prediction models. Understanding how genetics influence mammographic features is important because the mechanisms through which they are associated with breast cancer are not well known. Here, using mammographic screening history and detailed questionnaire data from 56,820 women from the KARMA prospective cohort study, we investigated the association between a genetic predisposition to breast cancer and mammographic features among women with a family history of breast cancer (N = 49,674) and a polygenic risk score (PRS, N = 9,365). The heritability of mammographic features such as dense area (MD), microcalcifications, masses, and density change (MDC, cm²/year) was estimated using 1,940 sister pairs. Heritability was estimated at 58% [95% confidence interval (CI), 48%–67%) for MD, 23% (2%–45%) for microcalcifications, and 13% (1%–25%)] for masses. The estimated heritability for MDC was essentially null (2%; 95% CI, −8% to 12%). The association between a genetic predisposition to breast cancer (using PRS) and MD and microcalcifications was positive, while for masses this was borderline significant. In addition, for MDC, having a family history of breast cancer was associated with slightly greater MD reduction. In summary, we have confirmed previous findings of heritability in MD, and also established heritability of the number of microcalcifications and masses at baseline. Because these features are associated with breast cancer risk and can improve detecting women at short-term risk of breast cancer, further investigation of common loci associated with mammographic features is warranted to better understand the etiology of breast cancer. Significance: These findings provide novel data on the heritability of microcalcifications, masses, and density change, which are all associated with breast cancer risk and can indicate women at short-term risk.

Background: Despite the biological link between thyroid hormones and breast cancer cell proliferation shown in experimental studies, little is known about the association between hyperthyroidism and breast cancer, as well as its association with the most common mammographic and genetic risk predictors for breast cancer. Methods: This study estimates the incidence rate ratios (IRRs) of breast cancer among women diagnosed with hyperthyroidism, compared to those who are not, using two cohorts: a Swedish national cohort of the general female population (n = 3,793,492, 2002–2011) and the Karolinska Mammography Project for Risk Prediction of Breast Cancer (KARMA, n = 69,598, 2002–2017). We used logistic regression to estimate the odds ratios (ORs) of hyperthyroidism according to the mammographic and genetic risk predictors for breast cancer. Results: An increased risk of breast cancer was observed in patients in the national cohort with hyperthyroidism (IRR = 1.23, 95% CI = 1.12–1.36), particularly for toxic nodular goiter (IRR = 1.38, 95% CI = 1.16–1.63). Hyperthyroidism was associated with higher body mass index, early age at first birth, and lower breastfeeding duration. Higher mammographic density was observed in women with toxic nodular goiter, compared to women without hyperthyroidism. Additionally, among genotyped women without breast cancer in the KARMA cohort (N = 11,991), hyperthyroidism was associated with a high polygenic risk score (PRS) for breast cancer overall (OR = 1.98, 95% CI = 1.09–3.60) and for estrogen receptor-positive specific PRS (OR = 1.90, 95% CI = 1.04–3.43). Conclusion: Hyperthyroidism is associated with an increased risk of breast cancer, particularly for patients with toxic nodular goiter. The association could be explained by higher mammographic density among these women, as well as pleiotropic genetic variants determining shared hormonal/endocrine factors leading to the pathology of both diseases.

Background High pre-pregnancy body mass index (BMI) and inappropriate gestational weight gain (GWG) are associated with adverse short and long-term maternal and neonatal outcomes and may act as modifiable risk factors on the path to overweight/obesity, but their social patterning is not well established. This study investigates the association of education with BMI and GWG across two consecutive pregnancies. Methods The study includes 163 352 Swedish women, having their first and second singleton birth in 1982–2010. In both pregnancies, we investigated the association of women's education with (1) pre-pregnancy weight status and (2) adequacy of GWG. We used multinomial logistic regression, adjusting for child's birth year, mother's age and smoking status. Results Overall, the odds of starting either pregnancy at an unhealthy BMI were higher among women with a low education compared to more highly-educated women. Lower education also predicted a greater increase in BMI between pregnancies, with this effect greatest among women with excessive GWG in the first pregnancy (p<0.0001 for interaction). Education was also inversely associated with odds of excessive GWG in both pregnancies among healthy weight status women, but this association was absent or even weakly reversed among overweight and obese women. Conclusions Lower educated women had the largest BMI increase between pregnancies, and these inequalities were greatest among women with excessive GWG in the first pregnancy. The importance of a healthy pre-pregnancy BMI, appropriate GWG and a healthy postpartum weight should be communicated to all women, which may assist in reducing existing social inequalities in body weight.