View Printable PDF Version (article below) |
Overview:
Breast Cancer and Abortion
Q-A: Why would a woman who has an induced abortion before her first full-term pregnancy (FFTP) suffer an increased risk of developing breast cancer?
A woman’s breast is especially
sensitive to carcinogenic (ie, cancer producing) influences 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 (ie, the female sexual hormones), and hCG (human
Chorionic Gonadotropin). All of these hormones, especially the latter, serve to
stimulate immature breast cells to mature into fully differentiated cells [1].
If this process is artificially interrupted by way of an induced abortion, the
hormone levels drop suddenly and 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 because 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).
Q-B: Do any animal models support the claim that abortions early in life increase breast cancer risk?
Yes. Russo and Russo, in their
classic work published in 1980 [2], studied several groups of rats which were
given a specific carcinogen (cancer producing agent) called DMBA. They
noted that 77% of the rats who underwent an abortion developed breast cancer
and 69% of the virgin rats developed breast cancer, but 0% of the rats who were
allowed to complete their pregnancy developed breast cancer.
Q-C: 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 2-fold increased risk
of breast cancer [3]. In 1981, Pike et al [4] published their notable work
showing that young women (under the age of 32) who had experienced an abortion
before their first full-term pregnancy (FFTP) had a 140% increased risk
of breast cancer. A number of studies followed but in 1994, Daling et al [5]
published a large study which noted that women who had an abortion before their
FFTP suffered a 40% increased risk. This risk increased to 150% if the
adolescent had her abortion before the age of 18. In addition, Daling et al
noted that if adolescents under the age of 18 aborted a baby that was more than
8 weeks old, they suffered an 800%
increased risk of developing breast cancer.
Finally, in 1996, in what is
openly regarded as the most meticulous and comprehensive meta-analysis
(ie, 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 [6] found that women who had an abortion before their FFTP had a 50% increased
risk of developing breast cancer whereas women who had an abortion after their
FFTP sustained a 30% increased risk.
Q-D: If Dr. Brind et al’s study was so conclusive, then why is the subject still being debated?
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.”
[7] Then in early 1997, the New England
Journal of Medicine published the results of a large prospective study by
Melbye et al [8] which claimed to show that abortion did not increase the risk
of breast cancer.
Q-E: Was there any problem with the study by Melbye?
Yes. It is astonishing that
the New England Journal of Medicine
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 New England Journal of Medicine [9]. 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
“cases” (ie, women who had an induced abortion) was less than 10 years, whereas it was over 20 years for the
“controls” (ie, women who did not have an induced abortion). A follow-up period of less than 10 years is
not long enough to show the effect of an abortion (ie, too short of a latent
period); 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; and 4) The study did
note that women who had an abortion after the 12th week sustained a 38%
increased risk of breast cancer, whereas women
who had late-term abortions (ie, after 18 weeks) had a statistically
significant increase of 89%. Both of these results received little media
attention.
Q-F: 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.” (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.) The recall bias hypothesis can be
defined as the following: “The hypothesis that people who develop a disease
(eg, breast cancer) are more likely than people who do not develop that disease
to admit that they participated in a ‘controversial risk factor’ (eg, an
induced abortion or oral contraceptive pill [OCP] use) for that disease.” In
essence 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.
Q-G: On what basis do such researchers make such a claim?
This claim of recall bias is based on a study by Lindefors-Harris et al
[10] from Sweden. She compared the responses of “cases” and “controls” to the
national register which reportedly keeps an accurate record of all women who
had an abortion. The study claimed to
show that in the group of women who indeed had an induced abortion (according
to the national register), the women who had breast cancer were about 50% more
likely to admit that they had the abortion than the women who did not have
breast cancer. The study has been criticized by Daling, a prominent
epidemiologist, who noted that the study actually showed only a 16% “recall
bias” (versus the reported 50% figure), when analyzed properly [5].
Q-H: Were there any problems with the study?
Yes. The study noted that 7
out of the group of 26 women with breast cancer who stated that they had an
abortion at a young age, actually did not have an abortion according to the
national register. This implies that 7 women out of the 26 women, or 27% of
these “cases,” stated that they had an abortion at a young age, when they
really did not. Obviously, this undermines the credibility of the study. Who
would place any confidence in a study in which more than one quarter of a group
of women with breast cancer reportedly lied and said they had an abortion when
they actually had not?
Q-I: Is there any way to get around the “recall bias” problem?
Yes. A direct way to “get
around it” 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 comparing 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 [11,12].
Q-J: Can the same technique be used in regard to the abortion and breast cancer studies?
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 could simply compare their
oral responses to that of the written medical record. Any degree of bias would
be recorded and accounted for.
Q-K: This seems so basic. Why has it not been done?
That is a good question.
Perhaps the question that should be asked is: Has someone done it and not
reported it for fear of going against the bureaucratic forces within the
political and medical establishments?
Q-L: Do women who had an abortion or miscarriage, or used oral contraceptive pills (OCPs) early in their reproductive life develop a more aggressive breast cancer?
Yes. Olsson et al has noted
[13]: “These results indicate that the rate of tumor cell proliferation [ie,
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. . .”
Q-M: Do miscarriages carry the same risk of breast cancer as induced abortion?
Women whose pregnancies end in
miscarriage usually do not experience the same increase in estradiol and
progesterone (ie, the female sexual hormones) or hCG levels that would result
from a healthy pregnancy. 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 first full-term pregnancy (FFTP) may
still carry a significant risk of developing breast cancer as noted in Table 2A
below. (Further research in this area is critical to determine if an early
miscarriage does indeed increase the risk of breast cancer.)
Table A:
RISKS OF
BREAST CANCER IN WOMEN WHO HAD A MISCARRIAGE BEFORE THEIR FIRST FULL
TERM PREGNANCY
AUTHOR |
YEAR OF PUBLICATION |
PERCENT CHANGE |
CONFIDENCE INTERVAL |
|
|
|
|
Pike et al [138] |
1981 |
151% increase |
unknown |
Brinton [101] |
1983 |
9% increase* |
0.8-1.5 |
Hadjimichael [107] |
1986 |
250% increase |
1.7-7.4 |
Rosenberg [149] |
1988 |
10% decrease* |
0.7-1.4** |
Ewertz/Duffy [106] |
1988 |
163% increase* |
0.83-8.32*** |
Adami [96] |
1990 |
20% increase* |
0.7-2.0 |
Daling [103] |
1994 |
10% decrease* |
0.6-1.3 |
Rookus [141] |
1996 |
40% increase* |
1.0-1.9 |
* This result reflects a
trend towards an increased or decreased risk but does not attain statistical
significance
** Inappropriate age matching
in this study: median age of "cases"
and “controls” were was 52 and 40 respectively
Q-N: Is the prognosis of a pregnant woman who currently has breast cancer improved if she has an induced abortion?
No. Clarck 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.” [20] 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.” [21].
Q-O: What should women be told in general about having an abortion at a young age and the risk of breast cancer?
Women who have an elective
abortion before their firstborn baby suffer at least a 50% increased risk
of developing 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 the age of 18, or those who have
additional risk factors, such as a positive family history or use of oral
contraceptives before a FFTP. (The person who is interested in an excellent
review article describing the physiologic reasons behind the link between
abortion and breast cancer should see Canty’s article [22].)
1. Russo J, Russo IH. Toward a physiological approach to breast cancer prevention. Cancer Epidemiology, Biomarkers and Prevention. 1994; 3: 353-364.
2. Russo J, Russo IH. Susceptibility of the mammary gland to carcinogenesis. Am J Pathol. 1980; 100: 497-512.
3. Segi M, et al. An epidemiological study on cancer in Japan. GANN. 1957; 48: 1-63.
4. Pike MC, Henderson BE, et al. Oral contraceptive use and early abortion as risk factors for breast cancer in young women. Br J Cancer. 1981; 43: 72-76.
5. Daling J, Malone K, et al. Risk of breast cancer among young women: relationship to induced abortion. J Natl Cancer Inst. 1994; 86: 1584-1592.
16. Brind J, Chinchilli M, et al. Induced abortion as an independent risk factor for breast cancer: a comprehensive review and meta-analysis. J Epidemiol Community Health. 10/ 1996; 50: 481-496.
17. Lagnado L. Study on abortion and cancer spurs fight. Wall Street Journal. Oct. 11, 1996.
18. Melbye M, Wohlfahrt J, et al. Induced abortion and the risk of breast cancer. N Engl J Med. 1997; 336: 81-85.
19. Brind J, et al. Induced abortion and the risk of breast cancer. N Engl J Med. 1997; 336: 1834.
10. Lindefors-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. Am J Epidemiol. 1991; 134: 1003-1008.
11. 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.
12. Rookus MA, Leeuwen FE. Oral contraceptives and risk of breast cancer in women ages 20-54 years. The Lancet. 1994; 344: 844-851.
13. 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.
14. Brinton LA, Hoover R, et al. Reproductive factors in the aetiology of breast cancer. Br J Cancer. 1983; 47: 757-762.
15. Hadjimichael OC, et al. Abortion before first live birth and risk of breast cancer. Br J Cancer. 1986; 53: 281-284.
16. Rosenberg L, Palmer JR, et al. Breast cancer in relation to the occurrence and time of induced and spontaneous abortion. Am J Epidemiol. 1988; 127: 981-989.
17. Ewertz M, Duffy SW. Risk of breast cancer in relation to reproductive factors in Denmark. Br J Cancer. 1988; 58: 99-104.
18. Adami HO, Bergstrom R, Lund E, Meirik O. Absence of association between reproductive variables and the risk of breast cancer in young women in Sweden and Norway. Br J Cancer. 1990; 62: 122-126.
19. Rookus M, Leeuwen F. Induced abortion and risk for breast cancer: reporting (recall) bias in a Dutch case-control study. J Natl Cancer Inst. 1996; 88: 1759-1764.
20. Clarck RM, Chua T. Breast cancer and pregnancy: the ultimate challenge. Clinical Oncology. 1989; 1: 11-18.
21. King RM, Welch JS, et al. Carcinoma of the breast associated with pregnancy. Surgery, Gynecology and Obstetrics. 1985; 160: 228-232.
22. Canty L. Breast cancer risk: Protective effect of an early first full-term pregnancy versus increased risk of induced abortion. Oncol Nurs Forum. 1997; 24: 1025-1031
Currently 28 of 37 Studies
Show an Induced Abortion Increases Risk of Breast Cancer