Breast Cancer and Abortion: Other Questions

Q-7W: Does the mammography controversy in any way diminish the fact that the major mesa-analyses show that both an abortion performed early in a woman's reproductive life and/or early OCP use increase a woman's risk of breast cancer?

No. Even though the rise in breast cancer may, in small part, be due to the increased use of mammography, it gives no reason for the discrepancy in breast cancer rates between women who did or did not have an abortion performed early in their reproductive life and/or who had early OCP use.

Q-7X: Do women who had "(non-specific) miscarriages" (ie, this category would include miscarriages that occur either before or after a woman's first full-term pregnancy (FFTP) have an increased risk of breast cancer?

Table 7A:
Risks of Breast Cancer To Women
Who Had A Miscarriage
Author Percent Change Year of Publication Confidence Interval
Dailing(2) 10% decrease* 1994 0.9 (0.7-1.2)
Hadjimichael43** no change 1986 unknown
La Vecchia44 10% decrease* 1987 0.9 (0.69-1.15)
Lipworth45 10% increase* 1995 1.1 (0.82-1.40)
Newcomb46 11% increase 1996 1.11 (1.02-1.20)
Parrazini47 no change 1992 1.0 (0.9-1.1)
Rohan48 20% increase* 1997 1.2 CI unknown
Rookus(5) 10% increase* 1996 1.1 (0.9-1.5)
Rosenberg(16) 30% increase* 1988 1.3 (0.8-2.2)
* This result reflects a trend toward an increased or decreased risk but does not attain statistical significance.
**Women who had their miscarriage after their first full-term pregnancy (FFTP).

Table 7A is a review of the major studies which gave data on the risk of breast cancer and miscarriages. It would appear that women who had "a non-specific miscarriage" would not have an elevated risk of breast cancer.

Q-7Y: Do the studies published after 1980 show that women who haue had a miscarriage before their FFTP have an increased rzsk for breast cancer?

Table 7B:
Risks of Breast Cancer In Women Who
Had A Miscarriage Before Their FFTP
Author Year of Publication Percent Change Confidence Interval
Adami49 1990 20% increase* 0.7-2.0
Brinton(28) 1983 9% increase* 0.8-1.5
Daling(2) 1994 10% decrease* 0.6-1.3
Ewertz/Duffy50 1988 163% increase* 0.83-8.32***
Hadjimichael(43) 1986 250% increase 1.7-7.4
Pike et al(15) 1981 151% increase unknown
Rookus(5) 1996 40% increase* 1.0-1.9
Rosenberg(16) 1988 10% decrease* 0.7-1.4**
* This result reflects a trend toward an increased or decreased risk but does not attain statistical significance.
** Inappropriate age matching in this study: median age of "cases" was 52; median age of "controls" was 40.
*** first trimester miscarriage in nulliparous women.

After reviewing the literature, Table 7B exhibits that 6 out of 8 studies show a trend and/or statistically significant increased risk of breast cancer with miscarriage before a first full-term pregnancy (FFTP). The studies noted here appear to show that a miscarriage before a FFTP does elevate the risk of breast cancer but further research is urgently needed to verify this. Hopefully researchers will perform a meta-analysis in this important area in the near future. This may have special implications for working mothers, who have been noted to have an increased risk of miscarriage. "After being adjusted for confounding factors, weekly job hours during the first trimester of pregnancy showed a strong independent association with spontaneous abortion risk; odds ratio 3.0 (1.4-.5.6)"51.

**** Calle et al52 noted that miscarriage before a woman's first term pregnancy did not result in an increased risk of fatal breast cancer (RR=0.76), but this prospective study may be particularly weak in measuring this variable for a number of reasons (see end of chapter for explanation).

Q-7ZI: Do multiple miscarriages before a woman's FFTP increase the risk?

Brinton et al(28) found that women who had two or more miscarriages before their FFTP had a relative risk of 2.16 (0.9-5.1), that is, a 116% increased trend toward developing breast cancer.* This is the result of only one study albeit, it does show a tendency toward increased risk.

*For the researchers in the audience: Lehrer et al65 noted that women who have breast cancer and had multiple miscarriages also have cancers which have a higher incidence of having less estrogen and progesterone receptors, thus carrying a worse prognosis. Whether the miscarriages had an effect on the breast or whether both the miscarriages and the low amount of receptors are a result of the "[genetic] condition" of that person is not known.

Q-7Z2: Does abortion increase the risk of cervical cancer?

Remennick(32) noted a strong statistically significant partial correlation coefficient between abortion rate and cervical cancer: (r = 0.63, p<O.05). A partial correlation coefficient gives an index of how related a risk is to an effect (breast cancer). No correlation would register as 0.0 whereas a perfect correlation would register as 1.0. A1though Zondervan et al53 and Daling(2) found no increased risk [RR= 0.66 (0.04-3.53)], several other studies have suggested a positive association between abortion and cervical cancer [54, 55-61]. Thomas, in his analysis of a WHO study, reported that women who had an induced abortion had at least a 160% increased risk of developing invasive cervical carcinoma62. Molina et al55 noted a 1.38-fold risk and Parrazini et al60 noted a 2.5-fold risk for cervical carcinoma with induced abortion. Le et al63 found nearly a 5-fold risk for cervical cancer in women reporting two or more abortions. Further study of this area is needed.

Addendum 7A: Calculations of estimated breast cancer mortality due to abortion.

In the early 1980s it was estimated that more than 1.6 million women had abortions each year64 and that about one-third were repeat abortions. If one counts only those women who are having their first abortion (so that one does not double count women), one estimates that about 1 million women were having their first abortions each year. In Daling's paper(2), of all the "controls" who had abortions, 45% had an abortion prior to their FFTP, 28% had an abortion after their FFTP, and 27% had an abortion and were nulliparous. If 1 million women had abortions for the first time each year this would mean that the respective groups would have 450,000, 280,000, and 270,000, women in them. The conservative rates of breast cancer increase in each of the respective groups based on Brind et al's paper is a 50% increase, a 30% increase, and a 30% increase. If we now use a 12% overall lifetime risk of breast cancer, and if the findings in Dr. grind's metaanalysis prove true in the long run, we can expect the following increases in breast cancer rates:

For women who had an abortion prior to their FFTP: 450,000 x 12% x 50% = 27,000;

For women who had an abortion after their FFTP: 280,000x 12%x30% = 10,080; and

For nulliparous women who had an abortion: 270,000 x 12% x 30% = 9,720.

Adding these together yields an estimate of 46,800 extra women who will be developing breast cancer each year because of abortion. Certainly, this is a low estimate because of the conservative manner in which the calculations were made. For example, estimates for high risk groups were not used: it was noted earlier that young women under the age of 18 who have an abortion performed early in their reproductive life have a 150% increased risk in breast cancer according to Daling(2). Also, the fact that about 500,000 women were having repeat abortions annually in the early 1980s could put these women at even greater risk. In addition, the national rate of breast cancer is even higher than 12% over the course of a woman's lifetime, and using the higher statistic would have increased the estimate even more than the 46,800 figure.

Addendum 7B: Why is the study by Calle a weak one?

Calle et al(52) enrolled 579,274 women who did not have breast cancer in a prospective study and recorded the information from those patients who both developed and died from breast cancer within 7 years of enrollment. There is a problem with this. A study such as this will only measure women who will both develop and die from breast cancer within a 7-year time frame. This implies that it will be studying those women who are developing particularly aggressive breast cancers. It is known that women who develop breast cancer at a young age tend to develop more aggressive cancers than those women who develop them at an older age66. Thus, in a large cohort of evenly distributed women from the age of 29 years old to over 70 years old, the study may well be focusing on younger women, which in itself narrows the focus of the study. It is also known that women who have early abortions or use OCPs at an early age have more aggressive cancer. Here again the study would be disproportionately focusing on this category of younger women.

A second point is that, if women who have early miscarriages are at increased risk of developing breast cancer, the study could have failed to identify them because it looked at only women who had both developed and died of their breast cancer within a 7-year period. Thus, even if miscarriages had resulted in a significantly increased risk of breast cancer, one may never have known this unless the subjects died from that breast cancer within the 7-year study period.


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