Risk of breast cancer among young women: relationship to induced abortion.

ABSTRACT

PIP: Epidemiologists compared data on 845 white women who were diagnosed with breast cancer between January 1983 and April 1990, were born after 1944, and lived in King, Pierce, or Snohomish counties in Washington State with data on 961 white women with no breast cancer from the same counties. They wanted to determine whether induced abortion increases the risk of breast cancer. Restricting cases to women born after 1944 allowed the researchers to focus only on legal induced abortions. When the researchers limited the analysis only to women who had been pregnant at least once, the risk of developing breast cancer in women who had had at least 1 induced abortion was 50% greater than those who had not had an induced abortion. This risk differed depending on the age at which the women underwent the induced abortion and the duration of that pregnancy. A gestational age (at the time of the first aborted pregnancy) of 9-12 weeks carried the highest risk of breast cancer (RR = 1.9 vs. 1.4 for =or 8 weeks and =or 13 weeks). Further, the breast cancer risk was greatest among women who underwent the induced abortion when they were less than 18 years old (relative risk [RR] = 2.5). It was especially high for women who were less than 18 years old and who had the abortion between 9 and 24 weeks of gestation (RR = 9). It was also high for those who were at least 30 years old at the time of the abortion (RR = 2.1). Spontaneous abortion was not associated with an increased risk (RR = 0.9). Neither the number of induced abortions nor the history of a completed pregnancy were associated with an increased risk of breast cancer. These findings suggest that an induced abortion during the last month of the first trimester increases the risk of breast cancer and that women who were at a very young age at the time of the first induced abortion face an increased risk of breast cancer.