Breast cancer and abortion
By Patrick Carroll

The article Breast cancer and abortion:collaborative reanalysis of data
from 53 epidemiological studies... (The Lancet Vol 363) 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 an English study it can be expected there is even more
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 50+ 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.

Yours sincerely

Patrick Carroll
PAPRI Pension And Population Research Institute
35 Canonbury Road
London N1 2DG
tel 020 7354 5667
fax 020 7226 6601
charity registration number in England 327942

References:

1. Beral V, Bull D, Doll R, Peto R, Reeves G. Collaborative Group of Hormonal Factors in Breast Cancer. Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83,000 women with breast cancer from 16 countries. Lancet 2004;363:1007-16.
2. Goldacre MJ, Kurina LM, Seagroatt V, Yeaates. Abortion and breast cancer: a case-control record linkage study. J Epidemiol Community Health 2001;55:336-337.