• We are sorry, but NCBI web applications do not support your browser and may not function properly. More information
Logo of bullwhoWHO Home PageBulletin Home PageBulletin Home PageAbout Bulletine-mail AlertSubmissions
Bull World Health Organ. 1970; 43(2): 209–221.
PMCID: PMC2427645

Age at first birth and breast cancer risk*


An international collaborative study of breast cancer and reproductive experience has been carried out in 7 areas of the world. In all areas studied, a striking relation between age at first birth and breast cancer risk was observed. It is estimated that women having their first child when aged under 18 years have only about one-third the breast cancer risk of those whose first birth is delayed until the age of 35 years or more. Births after the first, even if they occur at an early age, have no, or very little, protective effect. The reduced risk of breast cancer in women having their first child at an early age explains the previously observed inverse relationship between total parity and breast cancer risk, since women having their first birth early tend to become ultimately of high parity. The association with age at first birth requires different kinds of etiological hypotheses from those that have been invoked in the past to explain the association between breast cancer risk and reproductive experience.

Full text

Full text is available as a scanned copy of the original print version. Get a printable copy (PDF file) of the complete article (1.4M), or click on a page image below to browse page by page. Links to PubMed are also available for Selected References.

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Cole P, MacMahon B. Oestrogen fractions during early reproductive life in the aetiology of breast cancer. Lancet. 1969 Mar 22;1(7595):604–606. [PubMed]
  • DAO TL, SUNDERLAND H. Mammary carcinogenesis by 3-methylcholanthrene. I. Hormonal aspects in tumor induction and growth. J Natl Cancer Inst. 1959 Sep;23:567–585. [PubMed]
  • GILLIAM AG. Fertility and cancer of the breast and of the uterine cervix; comparisons between rates of pregnancy in women with cancer at these and other sites. J Natl Cancer Inst. 1951 Oct;12(2):287–304. [PubMed]
  • Kaplan SD, Acheson RM. A single etiological hypothesis for breast cancer? J Chronic Dis. 1966 Nov-Dec;19(11):1221–1230. [PubMed]
  • Lowe CR, MacMahon B. Breast cancer and reproductive history of women in South Wales. Lancet. 1970 Jan 24;1(7639):153–156. [PubMed]
  • MacMahon B, Cole P. Endocrinology and epidemiology of breast cancer. Cancer. 1969 Dec;24(6):1146–1151. [PubMed]
  • MacMahon B, Lin TM, Lowe CR, Mirra AP, Ravnihar B, Salber EJ, Trichopoulos D, Valaoras VG, Yuasa S. Lactation and cancer of the breast. A summary of an international study. Bull World Health Organ. 1970;42(2):185–194. [PMC free article] [PubMed]
  • Moon RC. Relationship between previous reproductive history and chemically induced mammary cancer in rats. Int J Cancer. 1969 May 15;4(3):312–317. [PubMed]
  • Salber EJ, Trichopulos D, MacMahon B. Lactation and reproductive histories of breast cancer patients in Boston, 1965-66. J Natl Cancer Inst. 1969 Nov;43(5):1013–1024. [PubMed]
  • STOCKS P. Social status in relation to carcinoma of the breast. Schweiz Z Pathol Bakteriol. 1955;18(4):706–717. [PubMed]
  • STOCKS P. The epidemiology of carcinoma of the breast. Practitioner. 1957 Sep;179(1071):233–240. [PubMed]
  • Valaoras VG, MacMahon B, Trichopoulos D, Polychronopoulou A. Lactation and reproductive histories of breast cancer patients in greater Athens, 1965-67. Int J Cancer. 1969 May 15;4(3):350–363. [PubMed]
  • WYNDER EL, BROSS IJ, HIRAYAMA T. A study of the epidemiology of cancer of the breast. Cancer. 1960 May-Jun;13:559–601. [PubMed]
  • Yuasa S, MacMahon B. Lactation and reproductive histories of breast cancer patients in Tokyo, Japan. Bull World Health Organ. 1970;42(2):195–204. [PMC free article] [PubMed]

Articles from Bulletin of the World Health Organization are provided here courtesy of World Health Organization


Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...


  • Cited in Books
    Cited in Books
    PubMed Central articles cited in books
  • MedGen
    Related information in MedGen
  • PubMed
    PubMed citations for these articles

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...