Because breast cancer has become such a pervasive and widespread condition, there has been a lot of speculation about what might be some of the true causes of this disease. Many theories have been offered and while some have been debunked, others have been verified by research and have been added to the list of known risk factors. Other theories are somewhere in the middle, having been neither confirmed nor refuted by the evidence, at least not in any clear way.
The theory that abortion and miscarriage can increase the chances of a woman eventually getting breast cancer has been placed at one time or another in all three of the above categories, depending on who has been doing the classifying. While the alleged connection between abortion and breast cancer has been a source of controversy - and no doubt will remain so because of the politics involved in the issue - an objective analysis of the studies that have been done does appear to give a definitive answer to the question. Whether all sides in the controversy are prepared to accept that answer is highly debatable.
The Early Studies
The idea that induced abortions or miscarriages could cause breast cancer came directly from a slew of studies that appeared to demonstrate just that. These studies were generally carried out between the 1970s and the 1990s using a methodology known as case-control. Two groups of women with breast cancer and without were asked about their history of abortions, and the answers were then compared for the purposes of analysis. After known risk factors had been accounted for, the results of some of these surveys showed that women with breast cancer were reporting greater numbers of abortions and miscarriages (which are known as spontaneous abortions). From this, it was concluded that abortion was in fact a risk factor for breast cancer. Since other studies were being done that showed the opposite, there was much confusion and disagreement among medical experts, while those involved in the social and political debate over abortion were left to pick and choose the data that supported their particular viewpoints.
Critiquing the Methodology
Close analysis of the situation uncovered a problem with the case-control methodology being used by many researchers. It was eventually discovered that women who had never had breast cancer were not always being completely forthcoming about their history of abortion, perhaps because of the stigma that is still attached to the procedure by some people. But women diagnosed with breast cancer were much more diligent about reporting abortions and miscarriages, most likely because their illness had already made it necessary to disclose their entire medical history to their doctors. In research this phenomenon is known as recall bias, and it is a distortion that can make personal testimony less than reliable in some situations.
In order to overcome the effects of recall bias, a different approach was tried using what is called prospective study design. Instead of quizzing two different groups of women on their abortion history, these studies restricted themselves to collecting information about abortion only from women who had never previously had breast cancer. These women were then followed over a period of years to see if they would develop breast cancer later on. When studies were carried out using this design, the connection between abortion and breast cancer risk suddenly disappeared, as the problem of recall bias had apparently been removed.
But there is a problem with this approach, too. Because the group being interviewed exclusively in these studies was the one which had been effected by recall bias, the unwillingness to disclose all about abortion history could still have played a distorting role in these survey results. The possibility exists that women who had not told the truth about past abortions were disproportionately represented among those who eventually developed breast cancer, which could act to hide a small increase in cancer risk connected to abortion.
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