Breast cancer: patterns and risk factors in older and younger women (June 2014) Breast cancer incidence is low in women under the age of 50 and has remained stable over the past three decades. While most breast cancer risk factors affect women throughout their lives, some vary with age and/or menopausal status. Screening is available for women ages 30–69 who are at high risk of breast cancer, and for women ages 50–74 who are at average risk. Older and younger women have strikingly different breast cancer incidence (new case) and mortality (death) rates, with the incidence and mortality rates in women over age 50 being significantly higher than those in women ages 30–49. The incidence patterns also vary by age group over time. The rate of new cases in women ages 30–49 have remained stable since 1981, whereas rates for women age 50 and older have decreased at a rate of 0.8% per year since 1999. However, both age groups have experienced similar declines over time in mortality. Younger women have seen a 3.2% per year mortality decrease since 1987 and women over 50 have seen a 2.5% per year decrease since 1994. Breast cancer was the most frequently diagnosed cancer in Ontario women in 2009, with 8,494 new cases diagnosed. Of these new cases, 1,825 (21.5%) were diagnosed in women ages 30–49 and 6,617 (77.9%) in women age 50 and older. In 2009, there were 1,885 deaths from breast cancer in women of all ages (215 for 30–49-year-old women and 1,664 for women age 50 and older). Age is the single most important risk factor for breast cancer, with incidence rising steeply between the ages of 30 and 65, which is why the Ontario Breast Screening Program (OBSP) screens women ages 50–74 at average risk for breast cancer with mammography every two years. Since research often uses age 50 as a proxy for menopause, it is not always clear whether it is age, menopausal status or both that account for some differences in risk factor effects.1 Hormone replacement therapy and oral contraceptive use, which modestly increase breast cancer risk, are prescribed according to whether a woman is pre- or post-menopausal. Reproductive and hormonal factors, such as number of full-term births (parity), age at menarche (the start of menstrual periods) and age at menopause, all influence hormone levels and have modest effects on breast cancer risk.2 Parity, breastfeeding and later age at menarche lower the risk of breast cancer, while fewer births, later age at first birth, earlier age at menarche and later age at menopause increase risk. Several of these reproductive and hormonal factors are more likely to affect the risk of estrogen-receptor (ER) and progesterone-receptor (PR) positive breast tumours.3 Breast cancers diagnosed before and around age 50 are more likely to be ER-negative or of other tumour types that tend to have poorer outcomes than the types more often diagnosed in older women.4 Although most factors are relevant for breast cancer risk throughout a woman’s life, the effect or the magnitude of risk may be greater at different ages. While alcohol consumption increases risk for women at all ages, recent alcohol intake may be more strongly related to risk for older women, although three or more drinks per day also increased risk in younger women.1 Obesity and physical activity have complex relationships with breast cancer risk. The risk associated with obesity varies according to hormone receptor and menopausal status.5 Obesity increases risk somewhat in post-menopausal women, but appears to protect against breast cancer before menopause. Physical activity has a modest protective effect on breast cancer risk, with stronger evidence for post-menopausal than pre-menopausal women. The risk of developing breast cancer for women with a history of the disease in a first-degree relative is stronger for younger women.1 Although family history may indicate a genetic predisposition to breast cancer, it may also reflect similar risk factor patterns (e.g., age at menarche or parity) within a family. Known genetic mutations carry substantially increased risk, but appear to account for only a small proportion of breast cancer cases. For other factors, risk appears to differ little between younger (pre-menopausal) and older (post-menopausal) women. Radiation therapy to the chest before age 30 increases breast cancer risk. Some types of benign breast disease substantially increase the risk of developing breast cancer.6 There is some evidence that night shift work may increase the risk of breast cancer.7 Women between the ages of 30 and 69 at high risk for breast cancer are eligible for screening with magnetic resonance imaging (MRI) combined with mammography every year in the OBSP High Risk Screening Program.8 Women are considered to be at high risk for breast cancer if they have any of the following risk factors: a genetic mutation that puts them at high risk for breast cancer; a parent, sibling or child who has a genetic mutation that puts them at high risk for breast cancer and have declined genetic testing; a family history that indicates a lifetime risk of breast cancer that is greater or equal to 25% confirmed through genetic assessment; or they received radiation therapy to the chest before 30 years of age and at least eight years ago as treatment for another cancer or condition (e.g., Hodgkin disease). Less than 1% of women in the general population are estimated to be at higher than average risk according to these criteria. Women at high risk develop breast cancer at an earlier age and their breast cancers tend to be more aggressive than breast cancers diagnosed in women at average risk. To find out more about breast cancer screening options, talk to your healthcare provider and visit the Screen for Life website at www.ontario.ca/screenforlife. References Trentham-Dietz A, Sprague BL, Hamptom JM, et al. Modification of breast cancer risk according to age and menopausal status: a combined analysis of five population-based case–control studies. Breast Cancer Res Treat. 2014;145:165–75. Cancer Care Ontario. Cancer Risk Factors in Ontario: Evidence Summary. Toronto, Canada, 2013. Althius MD, Fergenbaum JH, Garcia-Closas M, et al. Etiology of hormone receptor-defined breast cancer: A systematic review of the literature. Cancer Epidemiol Biomarkers Prev. 2004; 13:155868. Anderson WF, Pfeiffer RM, Dores GM. Comparison of age distribution patterns for different histopathologic types of breast carcinoma. Cancer Epidemiol Biomarkers Prev. 2006; 15:18991905. Suzuki R, Orsini N, Saji S, et al. Body weight and incidence of breast cancer defined by estrogen and progesterone receptor status—a meta-analysis. Int J Cancer. 2009;124(3):698712. Schnitt SJ. Benign breast disease and breast cancer risk: morphology and beyond. Am J Surg Pathol. 2003; 27(6):836–41. Kamdar BB, Tergas AI, Mateen FJ, et al. Night-shift work and risk of breast cancer: a systematic review and meta-analysis. Breast Cancer Res Treat. 2013; 138:291–301. Chiarelli AM, Prummel MV, Muradali D, et al. Effectiveness of screening with annual magnetic resonance imaging and mammography: Results of the initial screen from the Ontario High Risk Breast Screening Program. Journal of Clinical Oncology. 16 June 2014, available at http://jco.ascopubs.org/cgi/doi/10.1200/JCO.2013.52.8331; for a brief description of this paper’s findings, see https://www.cancercare.on.ca/highriskstudy. Citation: Cancer Care Ontario. Cancer Fact. Breast cancer: patterns and risk factors in older and younger women. June 2014. Available at http://www.cancercare.on.ca/cancerfacts. Prepared by staff in Prevention and Cancer Control.