The Studies

In 1996 there was a study published by Joel Brind et al named, "Induced abortion as an independent risk factor for breast cancer: a comprehensive review and meta-anaylsis."1

In 2018 a follow up study was published by Joel Brind et al named, "Induced Abortion as an Independent Risk Factor for Breast Cancer: a Systematic Review and Meta-anaylsis of Studies on South Asian Women."

The objective of the 1996 study was to determine if, due to a history of induced abortion, there was a significantly increased risk of breast cancer for women. The 2018 study focused on studies from South Asia and was carried out "to confirm the reality of the significant association reported in the first, 1996 review of induced abortion as a risk factor, independent of abortion's known effect in abrogating the protection afforded by full-term pregnancy."


1996 Brind et al Study

Definitions

A meta-analysis is a quantitative, formal, epidemiological study design used to systematically assess the results of previous research to derive conclusions about that body of research. Typically, but not necessarily, the study is based on randomized, controlled clinical trials."2


"An odds ratio of

• 1.0 (or close to 1.0) indicates that the odds of exposure among case-patients are the same as, or similar to, the odds of exposure among controls. The exposure is not associated with the disease.

• Greater than 1.0 indicates that the odds of exposure among case-patients are greater than the odds of exposure among controls. The exposure might be a risk factor for the disease.

• Less than 1.0 indicates that the odds of exposure among case-patients are lower than the odds of exposure among controls. The exposure might be a protective factor against the disease.

The magnitude of the odds ratio is called the “strength of the association.” The further away an odds ratio is from 1.0, the more likely it is that the relationship between the exposure and the disease is causal. For example, an odds ratio of 1.2 is above 1.0, but is not a strong association. An odds ratio of 10 suggests a stronger association."3

In this case the risk factor is not a disease but rather an induced abortion


First term pregnancy - the first pregnancy a woman has that ends in the birth of a child


Nulliparous woman - a woman who hasn't given birth to a child


Parous woman - a woman who has given birth to a child


1996 Brind et al Study

The meta-analysis included 23 independent studies base on 28 published reports and was done carefully. Studies which were excluded were those which did not specify whether the abortions were spontaneous or induced and those which only studied the effects of spontaneous abortion. 33 published reports were excluded because, although including data on abortion and breast cancer incidence they either only included spontaneous abortion or did not specify as to whether it was induced or spontaneous.

The results of this meta-analysis were that the overall odds ratio (OR) for any induced abortion exposure was 1.3 with a 95% confidence interval of 1.2, 1.4. The latter means that the authors have high confidence that any errors in the 1.3 OR will not lower the value below 1.2 or above 1.4.

The various ORs for the studies used are plotted in the figure below.



In their conclusions Brind et al report,

We believe that the present review and meta-analysis summarizes a literature that documents a remarkably consistent, significant positive association between induced abortion and breast cancer incidence, independent of the effect an induced abortion has in delaying first full term pregnancy. Moreover, the increased risk is seen in both prospective and retrospective studies from around the world, in populations with the widest imaginable differences in ethnicity, diet, socioeconomic and lifestyle factors and social morays, and which also differ widely in size and in many aspects of design, and whose data extend over more than half a century in time.

2018 Brind et al Study

The objective of this study according to the authors was,

South Asia, a historically low-incidence region for breast cancer, has produced many recent studies examining reproductive factors. We compiled these studies to confirm the reality of the significant association reported in the first, 1996 review of induced abortion as a risk factor, independent of abortion's known effect in abrogating the protection afforded by full-term pregnancy.

Indeed, the authors go on to state,

Moreover, the authors observed that the biological knowledge at the time reflected "a plausible and likely mechanism by which the surging oestradiol of the first trimester of any normal pregnancy, if it is aborted, may add significantly to a woman's breast cancer risk." Importantly, if these conclusions were correct, the impact on breast cancer incidence should be clearly evident by now, over 20 years later. This is especially true considering the worldwide expansion of legalized abortion during the late 20th century and the latency in the development of breast cancer. In fact, evidence abounds that supports this conclusion, especially as elective abortion has played its part in the "Westernization" of cultures in the developing world, such as in Asia.

The meta-analysis included 20 studies. In this meta-analysis all studies were included regardless of whether induced abortion was specified or simply reported as "abortion". The latter was included on the basis that spontaneous abortions do not increase breast cancer risk and a much higher proportion of reported abortions are now induced compared to those in the 1996 study.

The cumulative odds ratio (OR) for all 20 studies was 2.51 with a 95% confidence interval of 1.67 to 3.75. For the five studies reporting specific data on induced abortions (red highlighting in the figure below) it was 3.91 with a 95% Confidence interval of 1.02 to 14.97. All of the ORs for the 20 studies used are plotted in the figure below.



This paper concludes,

It has now been more than six decades since the first peer-reviewed evidence of induced abortion as a breast cancer risk factor appeared in the large nationwide study in Japan by Segi et al., two decades since the first review and meta-analysis of worldwide studies reported an overall significant link in worldwide studies, and one decade since Carroll's revelation of induced abortion as the single best predictor of breast cancer incidence in Europe. The present report documents the substantial literature of at least 20 new studies published just within the last decade in South Asia alone, summarizing a significant and moderately strong, dose-dependent association between abortion and breast cancer.

The authors go on to state

"Nevertheless, health ministries in the US and around the world, as well as medical associations and even voluntary anti-cancer organizations echo messages of denail of any effect of induced abortion on breast cancer risk."


The Reason

according to Huang 20135

During the first trimester of pregnancy, hormonal changes propel newly produced breast cells through a state of differentiation, a natural maturing process which greatly reduces the risk of breast cancer in the future. An interruption of this process by abortion will arrest this process before differentiation occurs, greatly raising the future risk of breast cancer in the future.

References:

1. Brind, J., et al. 1996. Induced abortion as an independent risk factor for breast cancer: a comprehensive review and meta-anaylsis.
2. Google search.
3. CDC. Interpreting Results of Case-Control Studies.
4. Brind, J., et al. 2018. Induced Abortion as an Independent Risk Factor for Breast Cancer: a Systematic Review and Meta-analysis of Studies on South Asian Women.
5. Huang, Y. et al. 2013. A meta-analysis of the association between induced abortion and breast cancer risk among Chinese females.