BREASTFEEDING
Abortions and Breast
Cancer
ABC Subject:
Breastfeeding
before age 20 reduces breast cancer risk by 80%
(new study in
American Journal of Public Health)
Dear Pamela Marcus (PhD),
Hello and thank you for your recent study of adolescent reproductive breast cancer risks.1 Two factors you covered are breastfeeding and induced abortion. Women under age 20 who breastfed reduced their BC risk by 80% (95% CI=0.1-0.6).1 Only women under age 20 who carry at least one pregnancy to term will have the possibility of this breastfeeding benefit. Your results in the area of reduced abortion show small risk increases but your sample size is too small to achieve 95% confidence of increased risk. As you may be aware, at least eighteen (18) studies in the field of 'ABC' (Abortion-Breast-Cancer') have achieved statistical significance with the result:
1. ONE study (Burany,
1979) reported that induced abortion DECREASED BC
risk
2. SEVENTEEN (17) studies reported that induced
abortion INCREASED BC risk
I.e. Over 94% of the statistically significant 'ABC' studies reported increased BC risk (see appendix).
Recall Bias in 'ABC' studies If women with breast cancer are more likely than controls to report induced abortions that they never had, then this would imply that the apparent 'ABC' risk may not exist. Such a theory of women imagining abortions that actually did not occur, may appear to be preposterous and bogus science. However, this is the basis of a 1991 study that reported seven Swedish women with BC (and one control) claiming induced abortions for which there was no SWEDISH record. The researchers labeled this 'over reporting' (imagining non-existent induced abortions).2 That these women very likely had these abortions outside Sweden (or inside Sweden but the procedure was recorded as something else) appears not to have crossed the minds of the researchers in 1991. In your 1999 AJPH report you refer to this study to justify possible 'reporting error' (i.e. recall bias).1 In 1998 the researchers of the Swedish study conceded that their over-reporting theory has no basis in fact:
"Some
women therefore had induced abortions abroad
or
unrecorded terminations of pregnancy [in Sweden]
We
are not surprised to find some Swedish women
confidently
reporting having had induced abortions
during the period
1966-1974 which are not recorded as
legally
induced abortions."3
These researchers have downgraded their 'ABC' 'recall bias' idea to the status of a "notion".3 Pamela Marcus, if you are aware of even one study that provides statistically significant proof of recall bias in 'ABC' studies, please provide that reference. One of the researchers that you reference in your AJPH article, Polly Newcomb, recently wrote:
"however, reproductive histories tend to be reported with a high degree of validity"4
You are rightly concerned about how reproductive factors affect BC risk in black American women. In 1993 the Journal of the National Medical Association reported that black women over the age of 49 years who had at least one induced abortion had an increased breast cancer risk of 370% (95% CI=2.6-8.4).5 It would take a very hefty dose of 'recall bias' to explain this result. And as you know, in a rat study those who had induced abortions had a 1300% increased risk of breast cancer.6 In rat studies there is no 'recall bias' possibility, since the rats are not interviewed. But, if they were, I'm sure they would not over-report.
REFERENCES
1 Marcus P, et al., AJPH, 1999;89:1244-1247
2 Meirik O, et al., American J Epidemiology, 1991; 134:1003-1008
3 Brind J, Meirik O, et al., J Epidemiology & Community Health, 1998;52: 209-212
4 Newcomb P, et al., American J Epidemiology, 1999;150:174-182
5 Laing AE, et al, J National Medical Association, 1993;85:931-939
6 Russo J, Russo I, American J Pathology, 1980;100:497-512
Mike Richmond, newscan@vcn.bc.ca
P.S. Appendix: The eighteen (18) statistically significant 'ABC' studies:
1. Bu et al., 1995. American Journal of Epidemiology, 141:S85
Induced abortion
increases risk of breast cancer
2. Burany B
(1979), Gestational characteristics
in women with
breast
cancer. Jugosl
Ginekol Opstet 19:237-247
(in Serbo- -
Croatian); induced
abortion DECREASES breast
cancer risk.
3. Daling JR,
et al. (1994), Risk of breast cancer among young women:
Relationship
to induced abortion.
J Natl Cancer Inst 86:1584-1592.
Women
who have an induced abortion before
age 18 +150%
have an increased breast
cancer risk of 150%.
4. Daling JR et
al. (1996), Risk of Breast Cancer among White Women
following
Induced Abortion, American J Epidemiology, 144:373-380.
Women
with no births (nulliparous) and at least one induced +100%
abortion have an
increased BC risk of 100% (95% CI=1.2-3.3.)
5. Ewertz M,
Duffy SW (1988),
Risk of breast cancer in relation to
reproductive
factors in Denmark.
Br J Cancer 58:99-104.
INDUCED +285%
abortion
increases BC risk by 285%.
6. Howe
HL, et al. (1989), Early abortion and breast cancer risk
among
women under age 40. Int J
Epidemiology 18:300-304. INDUCED
+90%
abortion
increased BC risk by 90%.
7. Laing
AE, et al. (1993), Breast cancer risk factors in African-American
women:
The Howard University
Tumor Registry Experience.
J
Natl Med Assoc 85:931-939.
Black women
of age 50 or older who had at least one INDUCED +370%
abortion
have an increased BC risk of 370%.
8. Le MG, et
al. (1984), Oral contraceptive use and breast or
cervical
cancer: Preliminary results of a French case-control
study.
In: Wolff J-P, Scott JS, eds. Hormones
and sexual factors
in human
cancer etiology. Amsterdam:
Elsevier, 139-147. INDUCED
abortion increases breast
cancer risk.
9. Lipworth
L, et al. (1995), Abortion
and risk of breast cancer:
a
case-control study in Greece. Int J
Cancer 61:181-184. INDUCED
abortion
before first full-term pregnancy increases
BC risk +106% by 106%.
10. Luporsi, 1988. British Journal of Cancer, 72:744-751.
Induced abortion increases risk of breast cancer
11 . Newcomb
PA, et al. (1995), Pregnancy
termination in relation to
risk
of breast cancer.
Am J Epidemiology 141:S54 (abstract #215). +23%
INDUCED
abortion increases BC risk by 23%.
12. Nishiyama
F (1982), The epidemiology of breast cancer in
Tokushima
Prefecture. Shikoku
Ichi 38:333-343 (in
Japanese). +
INDUCED
abortion increases
BC risk.
13. Palmer, 1996. American J Epidemiology, 1996;143:S32 ..
Induced
abortion
increases risk
of breast
cancer for nulliparous +40%
(i.e. childless)
women; the increase in risk was 40%.
14. Rohan et al., 1988. American Journal of Epidemiology, 128:478-489
Induced
abortion increases BC risk.
15. Rookus
MA (1995), Breast
cancer risk after induced abortion:
A Dutch
case-control study. Am J
Epidemiological 141:S54 +90%
(abstract
#214). INDUCED abortion increases
BC risk by 90%.
16. Rosenberg
et al., 1988. Breast Cancer in Relation to the
Occurrence and
Time of Induced and Spontaneous Abortion. Am.
J
Epidemiology, 127:981-989. Induced
abortion first occurring
after
the first term birth increased BC risk by 40% (95% CI= +40% 1.0-1.9)
17. Segi M, et
al. (1957), An epidemiological
study on cancer in Japan.
GANN 48 (Suppl): 1:63.
INDUCED abortion increases breast cancer risk.
18. Tavani A et
al. (1996). Abortion and Breast Cancer Risk.
International
J Cancer, 65:401-405. Women under
age 30 who abort +30%
a first pregnancy
increase BC risk by about 30%.