Cancer Causes & Control

, Volume 6, Issue 6, pp 519–524

Effect of twinship on incidence of cancer of the testis, breast, and other sites (Sweden)

  • M. Miles Braun
  • Anders Ahlbom
  • Birgitta Floderus
  • Louise A. Brinton
  • Robert N. Hoover
Research Papers

DOI: 10.1007/BF00054160

Cite this article as:
Braun, M.M., Ahlbom, A., Floderus, B. et al. Cancer Causes Control (1995) 6: 519. doi:10.1007/BF00054160

It has been suggested that cancers of the testis and breast are associated with exposure to estrogens and other hormones in utero. Twin pregnancies have higher levels of pregnancy-associated hormones than singleton pregnancies, and these levels may be higher in dizygotic than in monozygotic twin pregnancies. Through a large population-based study of twins, we assessed the hypothesis that levels of pregnancy-associated hormones have etiologic importance for cancers of the testis, breast, and other sites. The incidence of all cancers among 46,767 members of the Swedish Twin Registry was compared with the incidence among the Swedish general population. We found testicular cancer excess among dizygotic twins (observed/expected [O/E] ratio=1.6, 95 percent confidence interval [CI]=1.0–2.6) that was greater for men younger than 35 years (O/E ratio=2.3, CI=1.1–4.2) compared with older men (O/E ratio = 1.2, CI=0.5–2.4). In addition, a substantially elevated incidence of breast cancer was observed in dizygotic twin women aged 20 to 29 years (O/E=6.7, CI=2.9–13.1). None of the other age or zygosity groups showed notable elevations in incidence of testicular, breast, or other cancers. We conclude that dizygotic twinship may be associated with cancer of the breast and testis among young adults. These findings support the concept that pregnancy hormones are associated with risk of testicular and breast cancer, although non-hormonal aspects of twin pregnancy that vary with respect to zygosity cannot be excluded as explanatory factors.

Key words

Breast cancer cancer hormones prenatal exposure Sweden testis cancer twins 

Copyright information

© Rapid Science Publishers 1995

Authors and Affiliations

  • M. Miles Braun
    • 1
  • Anders Ahlbom
    • 1
    • 2
  • Birgitta Floderus
    • 1
    • 3
  • Louise A. Brinton
    • 1
  • Robert N. Hoover
    • 1
  1. 1.Environmental Epidemiology BranchUS National Cancer InstituteBethesdaUSA
  2. 2.Institute of Environmental MedicineKarolinska InstituteStockholmSweden
  3. 3.Department of NeuromedicineNational Institute of Occupational HealthSolnaSweden
  4. 4.Division of Biostatistics and Epidemiology, HFM-210, CBERFood and Drug AdministrationRockvilleUSA

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