Does this information come solely pro-life groups or Catholic bishops? No:
"BRCA1 and BRCA2 Mutation Carriers, Oral Contraceptive Use, and Breast Cancer Before Age 50" (Cancer Epidemiology, Biomarkers & Prevention, Oct. 2006)
"Estrogen Carcinogenesis in Breast Cancer," James D. Yager, Ph.D., and Nancy E. Davidson, M.D., New England Journal of Medicine, 354:270-282, 19 Jan. 2006.
"If it's not OK for him to take steroids...why is it OK for her?" (Breast Cancer Prevention Institute, 2006)
"Oral contraceptives and breast cancer review and meta-analysis" (Cancer, American Cancer Society, 1 Dec. 1990)
"Oral Contraceptives and Breast Cancer Risk Among Younger Women" (Journal of the National Cancer Institute, 31 March 1995)
"Oral Contraceptives and Cancer Risk" (National Cancer Institute Fact Sheet)
"The Birth Control Pill and Cancer Risk" (Breast Cancer Health Center / WebMD)
"Federal Study Confirms Contraception-Breast Cancer Link" (Tim Drake, National Catholic Register, 8 Jan. 2010)
"Surgeon: birth control pill a ‘molotov cocktail’ for breast cancer" (Kathleen Gilbert, LifeSiteNews, 6 Dec. 2010)
"Study: Abortion, Hormonal Contraceptives Influence Breast Cancer Risk" (John Jalsevac, LifeSiteNews, 8 Sep. 2009)
"Major U.S. Study Shows Oral Contraceptives Increase Breast Cancer Risk 44 %" (Gudrun Schultz, LifeSiteNews, 25 Oct. 2006)
"Abortion, Birth Control Pills, Raises Breast Cancer Risk" (Pam Stephan, About.com: Breast Cancer, 8 Jan. 2010)
"Injectable contraceptive doubles risk of breast cancer, study shows" (Monica Dybuncio, CBS News, 5 April 2012)
Dolle J, Daling J, White E, Brinton L, Doody D, et al. "Risk factors for triple-negative breast cancer in women under the age of 45 years," Cancer Epidemiol Biomarkers Prev 2009;18(4)1157-1166. [description]
Daling JR, Malone DE, Voigt LF, White E, Weiss NS. "Risk of breast cancer among young women: relationship to induced abortion," J Natl Cancer Inst 1994;86:1584-1592. [description]
White E, Malone KE, Weiss NS, Daling JR. "Breast cancer among young US women in relation to oral contraceptive use," J Natl Cancer Inst 1994;86:505-514. [description]
Daling JR, Brinton LA, Voigt LF, et al. "Risk of breast cancer among white women following induced abortion," Am J Epidemiol 1996;144:373-380. [description]
"Cancer Risk Among Women Taking Contraceptives Measured in Study" (ABC News, 6 March 2012)
Immoral or not, if something (like, e.g., smoking) is shown to have a direct relation to cancer, rational folks will (hopefully!) start listening.
One might argue that it is common sense (even before scientific medical studies are brought into it) to see that our messing around with the divinely designed human reproductive system was bound to have negative health effects. Sure enough . . .
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