Abortion & Breast Cancer FAQ

by Chris Kahlenborn, MD
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Why would a woman who has an induced abortion before her firstborn child suffer an increased risk of breast cancer?

A woman's breast is especially sensitive to carcinogenic (i.e., cancer producing) influence before she delivers her first child. When a woman becomes pregnant, a number of hormone levels increase dramatically in her body. Three especially notable ones are estradiol, progesterone (i.e., the female sexual hormones), and B-hCG (Beta-human Chorionic Gonadotropin). All of these hormones, especially the latter, serve to stimulate immature breast cells to mature into fully differentiated cells [145A]. If this process gets artificially interrupted, by way of an induced abortion, the hormone levels drop dramatically thereby suspending the natural process of maturation of many of the woman's breast cells. This is referred to as a "hormonal blow" by researchers. These cells are now "vulnerable" to carcinogens since they were left "in limbo": that is, they started the maturation process, but were never able to complete it. [Cells that have fully matured are less vulnerable to carcinogens than cells that are in the process of maturation].

Do any animal models support the claim that early abortions increase breast cancer risk?

Yes. Russo and Russo, in their classic work published in 1980 [144], studied several groups of rats which were given a specific carcinogen (cancer producing agent) called DMBA. They noted that 77% of rats who underwent an abortion developed breast cancer, while 0% [zero] of the rats who were allowed to complete their pregnancy developed cancer.

Could you tell me about the history of the abortion/breast cancer debate?

As early as 1957, Segi et al noted that women who had induced abortions had at least a two-fold risk in their rate of breast cancer [148]. In 1981, Pike et al published their notable work showing that young women (under age 32) who had experienced an abortion before their first live birth had a 140% increased risk of breast cancer. A number of studies followed but finally in 1994, Daling et al [103] published a large study which noted that women who had an abortion before first birth suffered a 40% increased risk, and that this increased to 150% if the abortion was before age 18.

Finally, in 1996, in what is openly regarded as the most meticulously comprehensive meta-analysis (i.e. a synthesis of all the major studies done in a particular field concluding in an overall risk for the pooled studies) of all the abortion/breast cancer research articles ever done, Brind et al [98] found that women who had an abortion before their first term child had a 50% increased of developing breast cancer while women who had an abortion after their first child sustained a 30% increased risk.

If Dr. Brind et al's study was so conclusive, then why is the subject still being debated?

That is a good question. Because of the controversy regarding abortion, Dr. Brind's study came under intense scrutiny, however, the results seemed irrefutable. Janet Daling -- a prominent epidemiologist (a researcher who studies trends in the medical field) -- was quoted in the Wall Street Journal as stating that Brind et al's results were "very objective and statistically beyond reproach." [104A] Then in early 1997, the New England Journal of Medicine (NEIM) published the results of a large prospective study by Melbye et al [128] which claimed to show that abortion did not increase the risk of breast cancer.

Was there any problem with the study by Melbye?

Yes. It is astonishing that the NEJM allowed it to be published in its submitted form. It had several glaring problems that have been pointed out in a follow up letter to the NEJM [128A]. The main ones include the following:

  1. Melbye's data actually pointed to a 44% increased risk of breast cancer due to abortion, but they never printed this result;
  2. The follow-up period for the "controls" was less than 10 years, while it was over 20 years for the "cases" (i.e. women who had an induced abortion). A follow-up period of less than ten years is not long enough to show the effect of an abortion;
  3. Over 30,000 women in the study who had abortions were "misclassified" as not having them -- thus 30,000 women were counted as not having abortions, when in fact they really had abortions;
  4. The study did note that women who had an abortion after the 12th week sustained a 38% increased risk of breast cancer, while women who had late term abortions (i.e. after 18 weeks) had a statistically significant increase of 89% -- both of these results received little media attention.

Dr. Melbye claimed that his study did not suffer from "recall bias". What did he mean by this?

Some researchers have claimed that "retrospective studies" suffer from "recall bias". They claim that women who have breast cancer are more likely to be truthful about the fact that they had an induced abortion than women who do not have breast cancer.

(An example of a retrospective study is one in which women with breast cancer would be interviewed and asked questions about their risk factors such as family history, induced abortion etc.)

On what basis do such researchers make such a claim?

This claim of recall bias is based on a study by Linderfors Harris et al [125] from Sweden. She compared the responses of "cases" and "controls" to the national register which reportedly keeps a record of all women who had an abortion. She noted that of the "cases" and "controls" who reportedly had an abortion as per the register, only 79% (19 of 24) of "cases" (i.e. the women who had breast cancer) and 73% (43 of 59) of "controls" admitted to having an abortion when they were interviewed. Thus, both groups tended to underreport abortions, but Linderfor-Harris noted that controls did so more often.

Where there any problems with the Linderfors Harris study?

Yes. The study noted that 7 of the 26 "cases" who stated that they had an early abortion, actually did not, according to the national register! This implies that 7 women out of 26, or 27% of the "cases" who stated that they had an early abortion, lied and said they did not! Obviously, this undermines the credibility of the study.

[Editor's note: As Brind has pointed out, this study assumed that if a woman's statement in an interview contradicted the register, she must be lying. An obvious alternative possibility is that the register is not 100% accurate.]

Is there any way to get around the "recall bias" problem?

Actually there is a fairly direct way to "get around it" and that is to measure it. Researchers did this already in the oral contraceptive and breast cancer debate in which some researchers claimed that women with breast cancer would be more honest about their history of oral contraceptive use. A number of studies refuted this claim by going back to a woman's medical records and compared the results of her interview response to that of the written record; all three of the studies that did this found less than a 2% difference between "case" and "control" responses [8, 26].

Can the same technique be used on the debate in regards to abortion and breast cancer?

Absolutely. Most good obstetricians and gynecologists obtain a thorough medical history of their patients especially on their initial visit. A standard question would be to ask a woman how many miscarriages and/or induced abortions she had. If one wished to measure the degree of "recall bias" between "cases" and "controls", one would simply have to compare their oral responses to that of the written medical record-any degree of bias could be recorded and accounted for.

This seems so basic-why has it not been done?

That is a good question. A more cynical question is: Has it been done already, without being reported, for fear of going against the "medically correct" establishment?

Do women who have used oral contraceptive pills (OCPs) early in life or had an early abortion develop more aggressive breast cancers?

Yes, Olsson et al has noted [92]: "these results indicate that the rate of tumor cell proliferation [i.e. rate of growth of cancer cells] is higher in patients with breast cancer who have used oral contraceptives at an early age or who at a young age have had an early abortion...".

Do miscarriages carry the same risk as induced abortion?

Women whose pregnancies end in miscarriage usually do not experience the same increase in estradiol and progesterone (the female sexual hormones) levels that a healthy pregnancy would result in. Therefore, when a woman experiences a miscarriage, there is a less dramatic shift in hormone levels and less of a "hormonal blow" to the breast. Studies have shown that miscarriages, in general, have less of a risk than induced abortions, however, several studies show that miscarriages before a full term birth may still carry a significant risk, e.g. Pike [138]: 140% increased risk; Brinton [101]: 90% increase; Hadjimichael [107]: 250% increase; Ewertz [106]: 163% increase; and Rookus [141]: 40% increase.

Is the prognosis of a pregnant woman who currently has breast cancer improved if she has an induced abortion?

No. Clark and Chua noted that: "Those [pregnant women with breast cancer] undergoing a therapeutic abortion had a poorer prognosis compared to a live birth and even a spontaneous abortion." [93] King et al. obtained a similar result. "... patients who had termination of the pregnancy had a five year survival rate of 43 percent, whereas patients who underwent mastectomy and who went to term had a five year survival of 59 percent." [94].

What should women be told in general about early abortion and the risk of breast cancer?

Women who have an elective abortion before their firstborn baby suffer at least a 50% increased risk in breast cancer according to the best meta-analysis done to date. The risks are almost certainly higher for women who have had an abortion before age 18, or those who have additional risk factors, such as a positive family history or use of oral contraceptives before first birth.


References

145A Russo J, Russo IH. Toward a physiological approach to breast cancer prevention. Cancer Epidemiology, Biomarkers and Prevention. 1994; 3:353-364.

144 Russo J. Tay TK, et al. Differentiation of the mammary gland and susceptibility to carcinogenesis. Breast Cancer Research and Treatment. 1982; 2:5-73.

148 Segi M, et al. An epidemiological study on cancer in Japan. GANN. 1957; 48:1-63.

103 Daling J, Malone K, et al. Risk of breast cancer among young women: relationship to induced abortion. JNCI. 1994; 86:1584-1592.

98 Brind J, Chinchilli M, et al. Induced abortion as an independent risk factor for breast cancer: a comprehensive review and meta-analysis. J. Epi. and Comm. Health. 10/ 1996; 50:481-496.

104A Lagnado L. Study on abortion and cancer spurs fight. Wall Street Journal. Oct. 11, 1996.

128 Melbye M, Wohlfahrt J, et al. Induced abortion and the risk of breast cancer. NEJM. 1997; 336:81-85.

128A Brind J et al. Induced abortion and the risk of breast cancer. NEJM. 1997; 336:1834.

125 Linderfors Harris BM, Eklund G, et al. Response bias in a case-control study: analysis utilizing comparative data concerning legal abortions from two independent Swedish studies. American Journal of Epidemiology. 1991; 134:1003-1008.

8 Chilvers C, McPherson K, et al. Oral contraceptive use and breast cancer risk in young women {UK National Case-Control Study Group}. The Lancet. May 6, 1989: 973-982.

26 Rookus MA, Leeuwen FE. Oral contraceptives and risk of breast cancer in women ages 20-54 years. Lancet. 1994; 344:844-851.

92 Olsson H, Ranstam J, et al. Proliferation and DNA ploidy in malignant breast tumors in relation to early contraceptive use and early abortions. Cancer. 1991; 67:1285-1290.

138 Pike MC, Henderson BE, et al. Oral contraceptive use and early abortion as risk factors for breast cancer in young women. British Journal of Cancer. 1981; 43:72-76.

101 Brinton LA, Hoover R. et al. Reproductive factors in the aetiology of breast cancer. British J. Med. 1983; 47:757-762.

107 Hadjimichael OC, et al. Abortion before first livebirth and risk of breast cancer. British J. of Cancer. 1986; 53:281-284.

106 Ewertz M, Duffy SW. Risk of breast cancer in relation to reproductive factors in Denmark. British J. of Cancer. 1988; 58:99-104.

141 Rookus M, Leeuwen F. Induced abortion and risk for breast cancer: reporting (recall) bias in a Dutch case-control study. JNCI. 1996; 88:1759-1764.

166 Staffa JA, Newschaffer CJ, et al. Progestins and breast cancer: an epidemiologic review. Fertility and Sterility. 1992; 57:473-491.

93 Clark RM, Chua T. Breast cancer and pregnancy: the ultimate challenge. Clinical Oncology. 1989; 1:11-18

13 Lee HP, Gourley L, et al. Risk factors for breast cancer by age and menopausal status: a case control study in Singapore. Cancer Causes and Control. 1992; 3:313-322.

94 King RM, Welch JS, et al. Carcinoma of the breast associated with pregnancy. Surgery, Gynecology and Obstetrics. 1985; 160:228-232.

231 Adam SA, Sheaves JK, et al. A case-control study of the possible association between oral contraceptives and malignant melanoma. British J. of Cancer. 1981; 41:45-50.


Chris Kahlenborn is an internist from Pittsburgh, PA. He is currently working on a book on the connection between abortion and breast cancer.
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Posted 9 Sep 2000.

Copyright 1998 by Chris Kahlenborn.
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