Abortions do not increase risk of breast cancer

It is known that previous pregnancy decreases the risk of breast cancer. But a new dissertation from the Karolinska Institutet in Sweden shows that even brief pregnancies terminated prior to full term can have a certain preventive effect. The results could not confirm several earlier studies showing that the risk of developing breast cancer increases among individuals who have had an abortion.

It has long been known that pregnancy has a preventive effect against breast cancer, but it is not known why. At the same time, several studies have indicated that abortions or miscarriages seem to increase the risk of breast cancer. This is refuted by a new dissertation from the Department of Medical Epidemiology and Biostatistics at the Karolinska Institutet.

We have looked a some 4,000 journals from maternity centers in which women have responded to standardized questions about abortions, among other things, and have not found any correlation between abortions and increased risk of breast cancer. In fact aborted pregnancies had some preventive effect in our study, says Gunnar Larfors, author of the newly defended dissertation.

Abortion is still a taboo subject in our society and also entails a trauma, so I believe that many women choose not to report an abortion if they are asked out on the street. But on the other hand, if you ask a person who has been afflicted with breast cancer about previous abortions, the probability is great that they will answer the question truthfully. This can skew the results to make it seem as if breast cancer is tied to abortion. In our study all women had answered the same question before developing breast cancer, says Gunnar Larfors.

A study from Denmark based on the Danish abortion register also found no correlation between abortions and increased risk of breast cancer.

Preventive effect unclear

The dissertation also rejects an earlier hypothesis about how pregnancy protects against breast cancer. A hormone that occurs in high levels during pregnancy, hCG, has evinced a preventive effect against breast cancer in experiments on rats and is already in use in clinical studies in the US.

But in several studies we have looked at women who have had extremely high levels of hCG, for example women with severe morning sickness, and have not been able to find any further risk reduction in them. This indicates that hCG is not the hormone to explain the reduced risk of breast cancer after pregnancy in humans, says Gunnar Larfors.

Title of dissertation: Pregnancy-related Risk Factors for Breast Cancer