Breast Cancer and Abortion

Commenting on the article "Breast cancer and abortion: collaborative re-analysis of data from 53 epidemiological studies" (The Lancet, Vol. 363, March 27, 2004), Patrick Carroll, of PAPRI (Pension and Population Research Institute, writes: "The article has its credibility impaired by the failure throughout the world to fully record induced abortions.

"This study places most weight on studies where abortion is measured prospectively before any diagnosis of breast cancer is made among the sample studied and the larger among these studies are especially weighted. Even in this country very few women declare induced abortions in such studies and the numbers of women both in the cancer group and in the control group of the Goldacre study in England, the largest study covered by this reanalysis, found only a small fraction of the women, that could have been expected to have had abortions from what is known from national incidence data, had a declared abortion history in either the cancer group or the control group. The median year of cancer diagnosis in this study was 1986. Cancers diagnosed then are likely to correspond to pregnancy related events such as live births and induced abortions that took place much earlier as in the 1960s. If there is such a large measure of under-recording in other countries, Great Britain is unusual in that there was liberalisation of the Abortion law at an early date when the 1967 Abortion Act took effect in 1968. Other countries liberalised later and many of the induced abortions relevant to this breast cancer investigation in other countries were illegal and even less likely to be declared than the abortions among women in a British study.

"National breast cancer incidence data in England is now showing an increase that is concentrated in the age group S0+ and the pregnancy related events that correspond to that can be investigated using national data that is correlational or ecological for successive birth cohorts of women given age specific data including data for abortions and nulliparous abortions. This also helps to explain the steeper reverse gradient in breast cancer incidence across social class now observed in the UK."