25 April 2007

USA: Another study refutes claimed abortion-breast cancer link

A study published in the Archives of Internal Medicine finds no association between either induced or spontaneous abortion and breast cancer.

Induced abortion has been inconsistently associated with breast cancer risk in case-control studies, write the authors. Retrospective cohort studies using registry information in Scandinavia have not suggested an increase in the incidence of breast cancer, although data on individual reproductive factors were not accounted for.

The authors examined the association between induced and spontaneous abortion and the incidence of breast cancer in a prospective cohort of young women, the Nurses’ Health Study II. The study included 105 716 women 29 to 46 years old at the start of follow-up in 1993. Information on induced or spontaneous abortions was collected in 1993 and updated biennially. During 973 437 person-years of follow-up between 1993 and 2003, 1458 newly diagnosed cases of invasive breast cancer were ascertained.

A total of 16 118 participants (15%) reported a history of induced abortion, and 21 753 (21%) reported a history of spontaneous abortions. The hazard ratio for breast cancer among women who had 1 or more induced abortions was 1.01 (95% confidence interval, 0.88-1.17) after adjustment for established breast cancer risk factors; among women with 1 or more spontaneous abortions, the covariate-adjusted hazard ratio was 0.89 (95% confidence interval, 0.78-1.01). The relation between induced abortion and the incidence of breast cancer did not differ materially by number of abortions, age at abortion, parity, or timing of abortion with respect to a full-term pregnancy.

The authors concluded that among this predominantly premenopausal population, neither induced nor spontaneous abortion was associated with the incidence of breast cancer.

Author Affiliations: Obstetrics and Gynecology Epidemiology Center, Department of Obstetrics and Gynecology (Drs Michels and Xue), and Channing Laboratory, Department of Medicine (Drs Michels, Colditz, and Willett), Brigham and Women’s Hospital, Harvard Medical School, and Departments of Epidemiology (Drs Michels, Xue, Colditz, and Willett) and Nutrition (Dr Willett), Harvard School of Public Health, Boston, Mass.

Induced and Spontaneous Abortion and Incidence of Breast Cancer Among Young Women: A Prospective Cohort Study. Karin B. Michels, ScD, PhD; Fei Xue, MD; Graham A. Colditz, MD, DrPH; Walter C. Willett, MD, DrPH. Archives of Internal Medicine 2007;167:814-820.