We set out to detect a transient increase in risk of breast cancer following childbirth, the existence of which has been postulated, but for which empirical evidence is contradictory. Breast cancers and births occurring among the cohort of Swedish women born after 1939 were linked, yielding 3,439 cases and 25,140 age-matched controls with at least two children. Within three years of their last childbirth, women had an estimated rate of breast cancer of 1.21 (95 percent confidence interval [CI]=1.02–1.44) times that of women whose last birth was 10 or more years earlier, after adjustment for parity and age at first birth. Further analyses suggested that this effect reflected, in part, a small transient increase in breast cancer risk that lasts for about three years following completed pregnancy. The effect of age at first birth on breast cancer risk appears to be confounded by time since last birth; the parity-adjusted rate ratio for having a first birth at age 35 years or more compared with under 20 years is reduced from 1.72 (CI=1.14–2.58) to 1.36 (CI=0.88–2.09) on additional adjustment for time since last birth. A transient increase in breast cancer risk after childbirth thus appears to account for part of the effect of age at first birth on breast cancer risk.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Dorn H. Cancer and marital status. Hum Biol 1943; 15: 73–9.
Logan WPD. marriage and childbearing in relation to cancer of the breast and uterus. Lancet 1953; ii: 1199–202.
MacMahon B, Cole P, Lin TM, et al. Age at first birth and breast cancer risk. Bull Wld Hlth Org 1970; 43: 209–21.
Leon DA. A prospective study of the independent effects of parity and age at first birth on breast cancer incidence in England and Wales. Int J Cancer 1989; 43: 986–91.
Kelsey JL, Gammon MD, John EM. Reproductive factors and breast cancer. Epid Reviews 1993; 15: 36–47.
Woods KL, Smith SR, Morrison JM. Parity and breast cancer: evidence of a dual effect. Br Med J 1980; 281: 419–21.
Miller WR. Breast cancer: Hormonal factors and risk of breast cancer. Lancet 1993; 341: 25–6.
Williams EMI, Jones L, Vessey MP, et al. Short term increase in risk of breast cancer associated with full term pregnancy. Br Med J 1990; 300: 578–9.
Bruzzi P, Negri E, La Vecchia C, et al. Short term increase in risk of breast cancer after first full term pregnancy. Br Med J 1988; 297: 1096–8.
Hsieh C-c, Goldman M, Pavia M, et al. Breast cancer risk in mothers of multiple births. Int J Cancer 1993; 54: 81–4.
Lambe M, Hsieh C-C, Trichopoulos D, et al. Transient increase in the risk of breast cancer after giving birth. N Engl J Med 1994; 331: 5–9.
Hsieh C-c, Pavia M, Lambe M, et al. Dual effect of parity on breast cancer risk. Eur J Cancer 1994; 30A: 969–73.
Adami HO, Bergstrom R, Lund E, et al. Absence of association between reproductive variables and the risk of breast cancer in young women in Sweden and Norway. Br J Cancer 1990; 62: 122–6.
Vatten LJ, Kvinnsland S. Pregnancy-related factors and risk of breast cancer in a prospective study of 29,981 Norwegian women. Eur J Cancer 1992; 28A: 1148–53.
Cummings P, Stanford JL, Daling JR, et al. Risk of breast cancer in relation to the interval since last full term pregnancy. Br Med J 1994; 308: 1672–4.
Cnattingius S, Ericson A, Gunnarskog J, et al. A quality study of a medical birth register. Scand J Soc Med 1990; 18: 143–8.
World Health Organization. International Classification of Diseases. Seventh Revision. Geneva, Switzerland: WHO, 1957.
Mattsson B. Completeness of Registration in the Swedish Cancer Registry (in Swedish). Stockholm, Sweden: National Board of Health and Welfare, 1977; Statistics of the National Board of Health and Welfare HS 1977: 15.
Lubin JH. Extensions of analytic methods for nested and population-based case-control studies. J Chron Dis 1986; 39: 379–88.
Jacobson HI, Thompson WD, Janerich DT. Multiple births and maternal risk of breast cancer. Am J Epidemiol 1989; 129: 865–73.
Breslow NE, Day NE. Statistical Methods in Cancer Research Volume 2. The Design and Analysis of Cohort Studies. Lyon, France: International Agency for Research on Cancer, 1987; IARC Sci. Pub. No. 82.
Preston DL, Lubin JH, Pierce DA, McConney ME. EPICURE Users Guide. Seattle, WA (USA): Hirosoft International Corporation, 1993.
Kalache A, Maguire A, Thompson SG. Age at last fullterm pregnancy and risk of breast cancer. Lancet 1993; 341: 33–6.
Editorial. Stem cells in neoplasia. Lancet 1989; i: 701–2.
Moolgavkar SH, Day NE, Stevens RG. Two-stage model for carcinogenesis: Epidemiology of breast cancer in females. JNCI 1980; 65: 559–69.
Pike MC, Spicer DV, Dahmoush L, et al. Estrogens, progesterones, normal breast cell proliferation, and breast cancer risk. Epid Reviews 1993; 15: 17–35.
Pike MC, Krailo MD, Henderson BE, et al. ‘Hormonal’ risk factors, ‘breast tissue age’ and the age-incidence of breast cancer. Nature 1983; 303: 767–70.
Rosner B, Colditz GA, Willett WC. Reproductive risk factors in a prospective study of breast cancer: the Nurses' Health Study. Am J Epidemiol 1994; 139: 819–35.
Talamini R, La Vecchia C, Franceschi S, et al. Reproductive and hormonal factors and breast cancer in a northern Italian population. Int J Epidemiol 1985; 14: 70–4.
Mirra AP, Cole P, MacMahon B. Breast cancer in an area of high parity: Saõ Paulo, Brazil. Cancer Res 1971; 31: 77–83.
Craig TJ, Comstock GW, Geiser PB. Epidemiologic comparison of breast cancer patients with early and late onset of malignancy and general population controls. JNCI 1974; 53: 1577–81.
Ewertz M, Duffy SW, Adami HO, et al. Age at first birth, parity and risk of breast cancer: A meta-analysis of 8 studies from the Nordic countries. Int J Cancer 1990; 46: 597–603.
Paffenbarger RS, Kampert JB, Chang HG. Characteristics that predict risk of breast cancer before and after menopause. Am J Epidemiol 1980; 112: 258–68.
Layde PM, Webster LA, Baughman AL, et al. The independent associations of parity, age at first full term pregnancy, and duration of breast feeding with the risk of breast cancer. J Clin Epidemiol 1989; 42: 963–73.
Brignone G, Cuisimano R, Dardanoni G, et al. A case-control study on breast cancer risk factors in a southern European population. Int J Epidemiol 1987; 16: 356–61.
Stavraky K, Emmons S. Breast cancer in premenopausal and postmenopausal women. JNCI 1974; 53: 647–54.
Lubin JH, Burns PE, Blot WJ, et al. Risk factors for breast cancer in women in Northern Alberta, Canada, as related to age at diagnosis. JNCI 1982; 68: 211–7.
Author information
Authors and Affiliations
Additional information
Ms Broeders contributed to the analyses during a three-month placement at LSHTM under the ERASMUS scheme.
Rights and permissions
About this article
Cite this article
Leon, D.A., Carpenter, L.M., Broeders, M.J.M. et al. Breast cancer in Swedish women before age 50: evidence of a dual effect of completed pregnancy. Cancer Causes Control 6, 283–291 (1995). https://doi.org/10.1007/BF00051403
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00051403