Select Committee on Science and Technology Written Evidence

Memorandum 26

Submission from Cape Hill Medical Centre


scientific developments relating to the abortion act 1967. Responding in particular to paragraphs 2(a) and 3


    —    Breast cancer rates have been rising in Europe and North America for several decades and are projected to rise further.1

    —    Oestrogen as well as promoting growth of healthy breast tissue is also recognized as a carcinogen.2

    —    Any factor which increases the development of cancer prone type 1 breast lobules at the expense of cancer resistant type 3 breast lobules could also increase a woman's long term risk of developing breast cancer.3

    —    As well as the undisputed effect of delay in first full term pregnancy being linked to breast cancer there is significant epidemiological evidence for an independent causal association between induced abortion and breast cancer; a majority of studies showing an association with no proven evidence of response bias; 17 statistically significant studies; observation of a dose effect;4 concordance of exposure with effect; a biologically plausible explanation;5 and experimental studies.6

    —    There are significant problems with the methodology of most of the recent prospective studies.

    —    It should be routine practice for anyone involved in counseling a woman considering an abortion, to provide as much information about possible risks of breast cancer pertaining to her decision as a reasonable patient would wish to know.


  1.  The age standardized incidence of breast cancer in the UK is among the highest in the world.7 The disease is the commonest cancer in Europe and the commonest cause of cancer death in women in Europe.8 Any factor which potentially affects this high incidence needs careful examination. Oestrogen overexposure is associated with breast cancer and oestrogen is a promoter of both normal and abnormal breast tissue.5 Induced abortion in animals is associated with mammary cancer6 and there are concerns that the same risks might accrue to women undergoing induced abortion. There are a majority of studies which show an increased risk, 17 of which are statistically significant on their own.

Age standardised (European) incidence and mortality
Rates, female breast cancer. GB 1975-2004

Year of diagnosis/death

  2.  Various guidelines and position papers have been published9, 10 which have suggested that there is no independent association between induced abortion and future risk of breast cancer. There is no dispute that delayed childbearing per se enhances breast cancer risk. 11 What is at issue is whether there might be (at least for some women) an additional risk conveyed by induced abortion.


  3.  The fully mature breast at the end of puberty contains mostly type one lobules which are incapable of producing milk. These type one lobules are more susceptible in later life to malignant change. Towards the end of pregnancy, type one lobules mature into milk producing type three lobules. The type three lobules are more cancer resistant and account for the majority of breast lobules in the post partum woman. A full term pregnancy therefore decreases life time risk of breast cancer, and oestrogen exposure before first full term pregnancy increases risk. Any factor which increases a woman's exposure to oestrogen surges before she has had the opportunity for the development of type three breast lobules potentially increases long term breast cancer risk.


  4.  Both the American College of Obstetricians and Gynecologists and the Royal College of Obstetricians and Gynaecologists in the UK have cited studies to support the position that doubt should be cast on the validity of case-control studies of abortion and breast cancer because of the possibility of response bias.

  5.  In the first of these two studies which look at women with histologically proven breast cancer, the authors provide figures comparing reported histories of abortion, with data on the Swedish national abortion registry. 12 They claim to have found evidence of abortion over reporting in women with breast cancer compared to controls, and underreporting of abortion in healthy women. Seven women with breast cancer claimed to have had an abortion when the computerized registry could find no record of this. The researchers made the daring assumption that the women were lying about having abortions they never had.

  6.  Ironically, the authors of the second paper gave the following comment on the Swedish study saying that "It would be highly unlikely for women to report an induced abortion that never took place, which shows that the registry was not complete." 13 Similar thoughts were expressed by Daling et al, "We believe that it is reasonable to assume that virtually no women who truly did not have an abortion would claim to have had one." Similarly, "These results argue against there being any substantial difference in the accuracy of reporting of induced abortions by women with cancer and women without cancer." 14

  7.  Eventually in 1998 Meirik, Adami and Eklund admitted that the Swedish abortion register was in fact not complete15 thus invalidating their figures.

  8.  In the second paper, Rookus and Van Leeuwen also claim underreporting of abortions in healthy control subjects. 16 Their evidence relied on a small group of parous women under age 45 containing only 13 subjects.

  9.  It remains to be argued why the working hypothesis would be that women with breast cancer are more likely to admit to having had abortions than women who are healthy? It would be equally—if not more—plausible to argue that women with breast cancer might be more likely to deny factors such as a history of abortion which may have contributed to their illness. In fact, it has been shown that in cases of cervical cancer, which is known not to be linked with abortion, no increase in the rate of reporting previous abortion was noted.

  10.  Researchers have tested for recall bias in women after abortion and found no credible evidence for it. 14, 17-19 The 2000 study by Tang et al concludes, "The authors data do not suggest that controls are more reluctant to report a history of induced abortion than are women with breast cancer".18


  11.  The RCOG 2004 guidelines refer to "the most methodologically rigorous of the previously reviewed studies ... those based on linkage of registry data" and the ACOG paper9 cites two of the most commonly referenced ones. 20, 21

  12.  The first of these looked at women born in Denmark between 1935 and 1978. 20 This study made the following errors:

    —    The study contains a population, some of whom were as old as 38 when the computerized abortion registry began. This indicates a skewed distribution towards older post abortion patients in the study.

    —    In the study, over 50% of the women with prior abortions were recorded as having had the abortion over 35 years of age. Yet we know from Danish government statistics that the median age of abortion is 27.

    —    The year of legalization of abortion in Denmark was stated in the paper to be 1973 whereas it was 1938.

    —    Abortions in Denmark were hand recorded from 1940 onwards although this fact is not mentioned in the paper. This means that up to 1973 about 60,000 women listed in the study cohort as not having had abortions in fact did have them.

    —    The average follow-up time for abortion-negative women was 21 years, whereas for abortion-positive women it was nine years.

  13.  So the older women, who are more likely to suffer from breast cancer, were counted as having no history of induced abortion resulting in significant underreporting of abortion history. 22, 23

  14.  Melbye et al also make adjustments for the birth cohort effect. This is the trend seen in birth cohorts of an increasing incidence in breast cancer after adjusting for age. If abortion is a significant reason why the incidence of breast cancer rose for most of the twentieth century, adjusting for the birth cohort effect eliminates the effect of the factor under study (abortion) and almost guarantees the nil result. Even allowing for these errors, Melbye et al still showed a 3% increased risk in breast cancer for each week of gestation, so that after 18 weeks an abortion would be associated with an 89% increase in risk.

  15.  In the Swedish register study, 41% of the cohort of breast cancer patients were nulliparous at the time of the index abortion. 21 This compared with a 49% nulliparity rate in the control group. Since nulliparity is associated with an increased risk of breast cancer the lack of correction for this in the study led to an underestimation of risk in the group exposed to abortion.


  16.  In 1999, Melbye and colleagues made corrections to errors to their earlier paper.4 Here they reported a 2.11 times increased risk in breast cancer among women who had pre-term delivery prior to 32 weeks gestation. An association between pre-term birth and later onset of breast cancer was also reported from Sweden in the same year, particularly with older women. 24 These results fit with the animal models of Russo and Russo6 and also give a further clue as to why abortion may be associated with subsequent increased breast cancer risk. It is now known that induced abortion is itself associated with an increased risk of subsequent pre-term delivery. 25, 26


  17.  Daling's study in 1994 showed an increased risk of breast cancer of 50% in aborted women overall. In addition, it identified various subgroups in which the risk was higher still. There was a relative risk of 2.5 in women who had abortions below the age of 18. In a subgroup of teenagers with a positive family history of breast cancer and who had undergone abortions, every woman had developed breast cancer by the age of 45. 14

  18.  It is interesting that the ACOG and RCOG guidelines groups fail to mention the 1989 prospective study by Howe et al. 29 This study showed a 90% increase in risk of breast cancer among women after abortion. There are now six studies which show a relative risk of greater than two, 27-32 and over 20 others showing an association between abortion and breast cancer. 14, 16, 17, 27, 33-52 Over half of these are statistically significant on their own. Brind and colleagues in their quantitative meta-analysis in 1996 found an odds ratio of breast cancer following abortion to be 1.3, with a ratio of 1.5 before the first term pregnancy. 25 In the review by Wingo et al53 published in the following year it is clear that a trend to increased risk of breast cancer exists after abortion. Particularly striking is the data on nulliparous women. There are nine such studies cited14, 17, 21, 35, 37, 38, 45, 50, 54 and seven of the nine show a positive association. 14, 21, 35, 37, 38, 45, 50


  19.  More evidence of an association is the study by Carroll1 using data from the Office of National Statistics. Breast cancer rates have been rising despite a decrease in women's age at first birth. However, nulliparous abortion rates show a marked increase in cohorts born during and since the 1940's. Since the majority of women now having abortions in the UK are nulliparous, Carroll estimates that up to 35% of new breast cancer cases could be attributable to abortion carried out perhaps decades previously. When the additionally carcinogenic effect of nulliparous abortions are taken into account, the figure rises to 52%. Projections from this data to the year 2023 suggest an eventual incidence of breast cancer of around 77,000 cases per year in the UK.


  20.  Since the year 2000 a number of studies have been published using prospective data and several have been cited by guidelines committees as evidence for a null association.

  21.  A study published by the Unit of Health-Care Epidemiology at Oxford University found a slightly lower than expected rate of abortion before breast cancer. 55 The authors, however, admitted a weakness in their data since the study by Goldacre et al found an incidence rate of induced abortion in the group of only 6.7% of the national incidence rate. 56

  22.  Two studies19, 57 on Chinese women have been published in addition to the 1995 abstract by Bu et al. 23 Both of these reported no or only slightly increased risk. Both studies acknowledged that the overwhelming majority of abortions in China take place after a live birth. 58 So, in a country with very high levels of abortion which make controls difficult to find, breast-cancer rates are not increasing for women who are mostly parous. This is in contrast with the UK where most abortions are performed before first full term pregnancy.

  23.  In Sweden a 2003 study reported a reduction in breast cancer risk with previous induced abortion. 59 This study was limited to pre-menopausal women. There has been a 45% increased incidence in breast cancer in Sweden in women aged 50-69 attributed to the introduction of screening but the expected fall in incidence after age 69 has failed to materialise.60 Like the other two record linkage studies mentioned, 20, 55 substantial amounts of data appear to be missing. 61

  24.  Other problems with cohort studies include:

    —    underpowering; 40, 62

    —    inadequate follow up time due to overlap of exposure and diagnostic periods20, 63-66 confounded by the transient effect of full term pregnancy; 63

    —    cohort effects; 66, 67

    —    missing information. 64, 68

  25.  The study by Brewster et al in Scotland 68 is a striking example of an unrepresentative sample since only 5.6% of its study population were nulliparous prior to having an abortion whereas 58% of abortions in Scotland are performed on nulliparous women.


  26.  The RCOG guidelines10 refer to "a major systematic review... which lent further support to these conclusions" arguing against a causal relationship between induced abortion and breast cancer. 69 The Collaborative Group on Hormonal Factors in Breast Cancer drew attention to the influence of parity in their 2002 report. 11 There was a 3% increase risk of breast cancer for every year of delayed childbearing. The figure of a 5% increased risk for pre-menopausal breast cancer and 3% increased risk for post-menopausal breast cancer for each year of delayed first full term pregnancy was similarly derived from an extensive literature review. 70

  27.  In Slovenia, a country which has not had much breast cancer screening, breast cancer incidence increased by 70% from 1971 to 1993. These changes were dominated by cohort effects, with the percentage of nulliparous women in the cohort the most important reproductive variable. 71

  28.  Induced abortion as a cause of delayed childbearing should therefore be considered a risk factor for breast cancer. In the Collaborative Group paper of March 2004 an argument was presented that compared prospective data with retrospective data. The authors concluded that the retrospective data are likely to be flawed because of "response bias" but failed to provide any credible evidence for this. Beral cites the study by Lindefors-Harris12 but fails to mention that the authors of this study retracted their claim of abortion over-reporting in 1998 as mentioned above.

  29.  A thorough analysis of the Lancet paper69 has been published by the Breast Cancer Prevention Institute. 72 Some of the more obvious errors are the following:

    (i)  Included are the prospective studies with substantially incomplete data. 4, 20, 55, 59

    (ii)  Excluded in the "totality of the worldwide epidemiological evidence" were 12 studies16, 29-31, 34, 37, 39, 44, 45, 47, 49, 50 for inappropriate reasons such as:

    (a)  "Principal investigators of four studies could not be traced",30, 37, 49, 50

    (b)  "original data could not be retrieved by the principal investigators",34, 39

    (c)  "researchers declined to take part in the collaboration",44, 45

    (iii)  Three studies were not even mentioned. 27, 28 These studies between them account for an 80% increased risk and 10 of the 15 are statistically significant alone.

  30.  As noted above, most of the studies which showed significant elevations in risk with induced abortion were inappropriately excluded from the analysis. Then, by combining certain groups of studies under the title of "other", it is made to look as if no study ever found a relative risk greater than 1.4. The reality is that six studies have reported overall relative risks greater than 2.0. 28-32, 73

  31.  The heading in the summary chart of the Lancet paper is misleading: "Relative risk of breast cancer, comparing the effects of having had a pregnancy that ended as an induced abortion versus effects of never having had that pregnancy." This is an inappropriate comparison; the proper one should be comparing women who have abortions with women who continue with the pregnancy.


  32.  A doctor's duty to explain risk to a patient extends to all risks which a reasonable doctor would disclose or those risks which a reasonable patient would attach significance. The state of Texas under the Woman's Right to Know Act now mandates that abortion providers tell women considering abortion about all possible complications—both immediate and long term—following abortion. Other US states have adopted similar legislation.

  33.  Kindley discusses the evidence from a lawyer's perspective and discusses what information a reasonable patient would consider material to her decision. 74 He concludes that information regarding the abortion breast cancer link is likely to be significant in the decision making process of a reasonable patient and therefore must be disclosed to women considering abortion. There have been three successful prosecutions of "failure to warn" cases brought in the US and in Australia and in the UK, The Chester v Afshar decision of 2004 swept aside the requirement of "causation" in "failure to warn" cases. 75

  34.  The abortion provider or abortion counselor may therefore be negligent by not informing women (especially nulliparous women) of a possible long term increased risk of breast cancer following induced abortion.


  35.  Women seeking advice or counseling regarding abortion are vulnerable and cannot make an informed decision without adequate information. Abortion providers are rarely neutral and women need more, and better quality information regarding long term risk of breast cancer whether they choose abortion or full term pregnancy.


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75  Chester v Afshar: UKHL 41, 2004.

September 2007

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