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- Nichols, Hazel B, et al.
(författare)
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Breast Cancer Risk After Recent Childbirth : A Pooled Analysis of 15 Prospective Studies
- 2019
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Ingår i: Annals of Internal Medicine. - : American College of Physicians. - 0003-4819 .- 1539-3704. ; 170:1, s. 22-30
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Tidskriftsartikel (refereegranskat)abstract
- Background: Parity is widely recognized as protective for breast cancer, but breast cancer risk may be increased shortly after childbirth. Whether this risk varies with breastfeeding, family history of breast cancer, or specific tumor subtype has rarely been evaluated.Objective: To characterize breast cancer risk in relation to recent childbirth.Design: Pooled analysis of individual-level data from 15 prospective cohort studies.Setting: The international Premenopausal Breast Cancer Collaborative Group.Participants: Women younger than 55 years.Measurements: During 9.6 million person-years of follow-up, 18 826 incident cases of breast cancer were diagnosed. Hazard ratios (HRs) and 95% CIs for breast cancer were calculated using Cox proportional hazards regression.Results: Compared with nulliparous women, parous women had an HR for breast cancer that peaked about 5 years after birth (HR, 1.80 [95% CI, 1.63 to 1.99]) before decreasing to 0.77 (CI, 0.67 to 0.88) after 34 years. The association crossed over from positive to negative about 24 years after birth. The overall pattern was driven by estrogen receptor (ER)-positive breast cancer; no crossover was seen for ER-negative cancer. Increases in breast cancer risk after childbirth were pronounced when combined with a family history of breast cancer and were greater for women who were older at first birth or who had more births. Breastfeeding did not modify overall risk patterns.Limitations: Breast cancer diagnoses during pregnancy were not uniformly distinguishable from early postpartum diagnoses. Data on human epidermal growth factor receptor 2 (HER2) oncogene overexpression were limited.Conclusion: Compared with nulliparous women, parous women have an increased risk for breast cancer for more than 20 years after childbirth. Health care providers should consider recent childbirth a risk factor for breast cancer in young women.Primary Funding Source: The Avon Foundation, the National Institute of Environmental Health Sciences, Breast Cancer Now and the UK National Health Service, and the Institute of Cancer Research.
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| 2. |
- Sandvei, Marie Søfteland, et al.
(författare)
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Menopausal hormone therapy and breast cancer risk : effect modification by body mass through life
- 2019
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Ingår i: European Journal of Epidemiology. - : Springer Science and Business Media LLC. - 0393-2990 .- 1573-7284. ; 34:3, s. 267-278
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Tidskriftsartikel (refereegranskat)abstract
- It is not known whether increased breast cancer risk caused by menopausal hormone therapy (HT) depends on body mass patterns through life. In a prospective study of 483,241 Norwegian women aged 50–69 years at baseline, 7656 women developed breast cancer during follow-up (2006–2013). We combined baseline information on recalled body mass in childhood/adolescence and current (baseline) body mass index (BMI) to construct mutually exclusive life-course body mass patterns. We assessed associations of current HT use with breast cancer risk according to baseline BMI and life-course patterns of body mass, and estimated relative excess risk due to interaction (RERI). Within all levels of baseline BMI, HT use was associated with increased risk. Considering life-course body mass patterns as a single exposure, we used women who “remained at normal weight” through life as the reference, and found that being “overweight as young” was associated with lower risk (hazard ratio (HR) 0.85, 95% confidence interval (CI) 0.76–0.94), whereas women who “gained weight” had higher risk (HR 1.20, 95% CI 1.12–1.28). Compared to never users of HT who were “overweight as young”, HT users who either “remained at normal weight” or “gained weight” in adulthood were at higher risk than expected when adding the separate risks (RERI 0.52, 95% CI 0.09–0.95, and RERI 0.37, 95% CI − 0.07–0.80), suggesting effect modification. Thus, we found that women who remain at normal weight or gain weight in adulthood may be more susceptible to the risk increasing effect of HT compared to women who were overweight as young.
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