A woman gains protection from breast cancer by completing a full-term pregnancy. In utero, her offspring produce hormones that mature 85 percent of the mother's breast tissue into cancer-resistant breast tissue. If the pregnancy ends through an induced abortion or a premature birth before thirty-two weeks, the mother's breasts will have only partially matured, retaining even more cancer-susceptible breast tissue than when the pregnancy began. This increased amount of immature breast tissue will leave the mother with more sites for cancer initiation, thereby increasing her risk of breast cancer. Hormonal contraceptives increase breast-cancer risk by their proliferative effect on breast tissue and their direct carcinogenic effects on DNA. Hormonal contraceptives include estrogen-progestin combination drugs prescribed in any manner of delivery: orally, transdermally, vaginally, or intrauterine. This article provides the detailed physiology and data that elucidate the mechanisms through which induced abortion and hormonal contraceptives increase breast-cancer risk.
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References
1.
Those studies that show a statistically significant link between abortion and breast cancer are as follows: SegiM., “An Epidemiological Study on Cancer in Japan,”GANN (Japanese Journal of Cancer Research) 48 suppl. (1957): 1-63; L. Rosenberg, et al., “Breast Cancer in Relation to the Occurrence and Time of Induced and Spontaneous Abortion,” American Journal of Epidemiology 127 (1988): 981-989; H.L. Howe, et al., “Early Abortion and Breast Cancer Risk Among Women Under Age 40,” International Journal of Epidemiology 18 (1989): 300-304; A.E. Laing, et al., “Breast Cancer Risk Factors in African-American Women: The Howard University Tumor Registry Experience,” Journal of the National Medical Association 85 (1993): 931-939; A.E. Laing, et al., “Reproductive and Lifestyle Factors for Breast Cancer in African-American Women,” Genetic Epidemiology 11 (1994): A300; J.R. Daling, et al., “Risk of Breast Cancer among Young Women: Relationship to Induced Abortions,” Journal of the National Cancer Institute 86 (1994): 1584-1592; J.R. Daling, et al., “Risk of Breast Cancer among White Women Following Induced Abortion,” American Journal of Epidemiology 144 (1996): 373-380; P.A. Newcomb, et al., “Pregnancy Termination in Relation to Risk of Breast Cancer,” Journal of the American Medical Association 275 (1996): 283-287; J.R. Palmer, et al., “Induced Abortion in Relation to Risk of Breast Cancer (United States),” Cancer Causes Control 8 (1997): 841-849; F. Nishiyama, “The Epidemiology of Breast Cancer in Tokushima Prefecture,” shikoku Ichi 38 (1982): 333-343 (in Japanese); M.G. Le, et al., “Oral Contraceptive Use and Breast or Cervical Cancer: Preliminary Results of a French Case-Control Study,” in Hormones and Sexual Factors in Human Cancer Aetiology, eds. J.P Wolff and J.S. Scott (Amsterdam: Elsevier, 1984), 139-147; L. Lipworth, et al., “Abortion and the Risk of Breast Cancer: A Case-Control Study in Greece,” International Journal of Cancer 61 (1995): 181-184; M.A. Rookus and F.E. van Leeuwen, “Induced Abortion and Risk for Breast Cancer: Reporting (Recall) Bias in a Dutch Case-Control Study,” Journal of the National Cancer Institute 88 (1996): 1759-1764; L. Bu, et al., “Risk of Breast Cancer Associated with Induced Abortion in a Population at Low Risk of Breast Cancer,” American Journal of Epidemiology 141 (1995): S85 (abstract 337); R. Talamini, et al., “The Role of Reproductive and Menstrual Factors in Cancer of the Breast Before and After Menopause,” European Journal of Cancer 32A (1996): 303-310; E. Luporsi, unpublished study (1988) data used in N. Andrieu, et al., “Familial Risk, Abortion and Their Interactive Effect on the Risk of Breast Cancer—A Combined Analysis of Six Case-Control Studies,” British Journal of Cancer 72 (1995): 744-751; T.E. Rohan, “A Population-Based Case-Control Study of Diet and Breast Cancer in Australia,” (1988), in Andrieu, “Familial Risk, Abortion”; J. Brind, et al., “Induced Abortion as an Independent Risk Factor for Breast Cancer: A Comprehensive Review and Meta-Analysis,” Journal of Epidemiology and Community Health 50 (1996): 481-496.
2.
Collaborative Group on Hormonal Factors in Breast Cancer, “Breast Cancer and Abortion: Collaborative Reanalysis of Data from 53 Epidemiological Studies, Including 83,000 Women with Breast Cancer from 16 Countries,”Lancet363 (2004): 1007–1016.
3.
LanfranchiA.“The Abortion Breast Cancer Link Revisited,” Ethics & Medics 29.11 (November 2004): 1-3; Brind, et al., “Induced Abortion as an Independent Risk Factor,” 481-496; J. Brind, “Induced Abortion as an Independent Risk Factor for Breast Cancer: A Critical Review of Recent Studies Based on Prospective Studies,” Journal of the American Physicians and Surgeons 10 (2005): 105-110; idem, “The Abortion-Breast Cancer Connection,”National Catholic Bioethics Quarterly5 (2005): 303–329.
4.
RussoJ.“The Protective Role of Pregnancy in Beast Cancer,”Breast Cancer Research7 (2005): 131–142.
5.
LanfranchiA.“The Federal Government and Academic Texts as a Barrier to Informed Consent,”Issues in Law and Medicine13 (2008): 12–15.; J. Brind, “Early Reproductive Events and Breast Cancer: A Minority Report,” paper given at the NCI workshop “Early Reproductive Events and Breast Cancer,” February 24-26, 2003, Bethesda, MD, http://www.bcpinstitute.org/nci_minority_rpt.htm.
6.
CoglianoV. (2005 working group), Carcinogenicity of Combined Estrogen-Progestogen Contraceptives and Combined Estrogen-Progestogen Menopausal Therapy (Lyons, France: World Health Organization International Agency for Research on Cancer, 2007).
7.
RussoJ., and RussoH.“Development of the Human Mammary Gland,” in The Mammary Gland, eds. NevilleM., and DanielC. (New York: Plenum Publishing Corporation, 1987).
8.
StewartD.“Enhanced Ovarian Steroid Secretion before Implantation in Early Human Pregnancy,”Journal of Clinical Endocrinology & Metabolism76 (1993): 1470–1478.
9.
Williams Obstetrics, 21st ed. eds. CunninghamF.G. (New York: McGraw-Hill, 2001), ch. 33, 856–869.
10.
WilcoxA.J.“Incidence of Early Loss of Pregnancy,”New England Journal of Medicine319 (1988): 189–194.
11.
LanfranchiA.“The Science, Studies and Sociology of the Abortion Breast Cancer Link,”Issues in Law and Medicine21 (2005): 95–108.
12.
BoeckerW.“The Normal Breast,” in Preneoplasia of the Breast: A New Conceptual Approach to Proliferative Breast Disease, ed. BoecherW. (Munich: Elsevier Saunders, 2006), 1–28.
13.
RussoJ.“Full-Term Pregnancy Induces a Specific Genomic Signature in the Human Breast,”Cancer Epidemiology Biomarkers and Prevention17 (2008): 51–66.
14.
RussoI., and RussoJ.“Review Mammary Gland Neoplasia in Rodent Studies,”Environmental Health Perspectives, 104 (1996): 938–967.
15.
MelbyeM.“Induced Abortion and the Risk of Breast Cancer,”New England Journal of Medicine336 (1997): 81–85.
16.
Russo, and Russo“Development of the Human Mammary Gland.”
17.
LambeH.“Parity, Age at First and Last Birth, and Risk of Breast Cancer: A Population Study in Sweden,”Breast Cancer Research and Treatment38 (1996): 305–311.
18.
RussoJ.“Chapter 1: Developmental, Cellular, and Molecular Basis of Human Breast Cancer,”Journal of the National Cancer Institute Monographs 2000.27 (2000): 17–37.
19.
RussoJ.“Full-Term Pregnancy Induces a Specific Genomic Signature”; I. Verlinden, et al., “Parity-Induced Changes in Global Gene Expression in the Human Mammary Gland,”European Journal of Cancer Prevention14 (2005): 129–137.
20.
Russo, and Russo“Development of the Human Mammary Gland.”
21.
Collaborative Group on Hormonal Factors in Breast Cancer, “Breast Cancer and Breast Feeding: Collaborative Reanalysis of Individual Data from 47 Epidemiological Studies in 30 Countries, including 50302 Women with Breast Cancer and 96973 Women without the Disease,”Lancet360 (2002): 187–195.
22.
BlackwellR.“Epidemiology of Breast Cancer,” in Diagnosis and Management of Breast Disease, ed. BlackwellR., and GrottingJ. (Cambridge, MA: Blackwell Science, 1996), 135–148.
23.
RussoJ.“Cancer Risk Related to Mammary Gland Structure and Development”Microscopy Research and Technique52 (2001): 204–223.
24.
MelbyeM.“Preterm Delivery and Risk of Breast Cancer,”British Journal of Cancer80 (1999): 609–613; C. Hsieh, et al., “Delivery of Premature Newborns and Maternal Breast Cancer Risk,” Lancet 353 (1999): 1239.
25.
VattenL.“Pregnancy Related Protection Against Breast Cancer Depends on Length of Gestation,”British Journal of Cancer87 (2002): 289–290.
26.
SwingleH.“Abortion and Risk of Subsequent Preterm Birth: A Systematic Review and Meta-Analyses,” Journal of Reproductive Medicine 54 (2009): 95-108; B. Rooney and B. Calhoun, “Induced Abortion and Risk of Later Preterm Births,”Journal of the American Physicians and Surgeons8 (2003): 46–49.
27.
LAME. Himpens“Prevalence, Type and Distribution and Severity of Cerebral Palsy in Relation to Ggestational Age: A Meta-Analytic Review,”Developmental Medicine & Child Neurology50 (2008): 334–340.
28.
Russo, and Russo“Development of the Human Mammary Gland.”
29.
Daling“Risk of Breast Cancer among Young Women.”
30.
Daling“Risk of Breast Cancer among Young Women.”
31.
LandC.E.“Incidence of Female Breast Cancer among Atomic Bomb Survivors, Hiroshima and Nagasaki 1950-1990,”Radiation Research160 (2003): 707–717.
32.
KhalenbornC.“Oral Contraceptive Use as a Risk Factor for Premenopausal Breast Cancer: A Meta-Analysis,”Mayo Clinic Proceedings81 (2006): 1290–1302.
33.
BandP.R.“Carcinogenic and Endocrine Disrupting Effects of Cigarette Smoke and Risk of Breast Cancer,”Lancet360 (2002): 1033–1034.
34.
LambeM.“Transient Increase in the Risk of Breast Cancer after Giving Birth,”New England Journal of Medicine331(1994): 5–9.
35.
Khalenborn“Oral Contraceptive Use as a Risk Factor.”
36.
Lambe“Transient Increase in the Risk of Breast Cancer.”
37.
ClarkR.M., and ChuaT.“Breast Cancer and Pregnancy: The Ultimate Challenge,”Clinical Oncology (Royal College of Radiologists)1 (1989): 11–18.
38.
AlavaradoM.V.“Immunolocalization of Iinhibin in the Mmammary Ggland of Rrats Ttreated with hCG,” Journal of Histochemistry and Cytochemistry 41 (1993 41): 29-34; I.H. Russo, et al., “Comparative Study of the Influence of Pregnancy and Hormonal Treatment on Mammary Carcinogenesis,”British Journal of Cancer64 (1991): 481–484.
39.
JanssensJ.P.“Human Chorionic Gonadotropin (hCG) and Prevention of Breast Cancer,”269 (2007–): 93–98.
40.
Clark, and Chua“Breast Cancer and Pregnancy.”
41.
RoganE.“Relative Imbalances in Estrogen Metabolism and Conjunction in Breast Tissue of Women with Carcinoma: Potential Biomarkers of Susceptibility to Cancer,”Carcinogenesis24 (2003): 697–702.
42.
CoglianoV.V“Carcinogenicity of Ccombined Ooestrogen-Pprogestoagen Ccontraceptives and Mmenopausal Ttreatment,”Lancet Oncology6 (2005 Aug 6): 552–553; Cogliano, et al., Carcinogenicity of Combined Estrogen-Progestogen Contraceptives and Combined Estrogen-Progestogen Menopausal Therapy.
