Abortion and Breast Cancer
Pregnancy: A Woman’s Natural Way of Resisting Breast Cancer
Carrying a pregnancy to full-term gives women natural resistance to breast cancer. During pregnancy, the breast tissues, called lobules, go through four stages of development. (A lobule is a unit of breast tissue consisting of a milk duct and glands.) During adolescence, the majority of lobules are Type 1 and Type 2, which are immature and susceptible to cancer. Throughout the first trimester of pregnancy, the number of Type 1 and 2 lobules rapidly increases. This means that the breast has more lobules susceptible to cancer. However, in the second trimester, the breast lobules start maturing into Type 4 lobules, which are cancer resistant. By the end of the third trimester, 85% of the breast has fully matured. Only 15% of the lobules remain immature and cancer-susceptible, leaving fewer opportunities for cancer to start. After birth and weaning, Type 4 lobules regress to Type 3. There is evidence this transition to Type 3 is permanent, providing life-long cancer resistance.
Chemical Abortion
Chemical abortion pills cause the termination of a healthy pregnancy. Chemical abortions take place in the first trimester (through week 10) when Type 1 and 2 breast lobules are forming rapidly. Since chemical abortions and surgical abortions both prematurely end healthy pregnancies, they carry the same risks for breast cancer.(3)
What about miscarriages?
Approximately 90% of miscarriages occur in the first trimester. However, the vast majority of natural miscarriages in the first trimester do not increase the risk of breast cancer. In these cases, pregnancy hormones are lower than those of a healthy pregnancy due to either a fetal or ovarian abnormality. Therefore, a breast may not have grown more, or at least grew very few, Type 1 and 2 lobules (sites where cancer starts) in response to pregnancy hormones.
For this information and more about breast cancer and abortion-related breast cancer risk, visit the
Breast Cancer Prevention Institute.
How does abortion affect this process?
A premature delivery before 32 weeks doubles the risk of breast cancer because it leaves the breast with more places for cancer to start. In the same way, abortion also stops the progression of breast lobule development. This prevents the development of Type 4, and subsequently Type 3, cancer-resistant lobules. Induced abortion of a healthy pregnancy results in increased risk of breast cancer for the mother because more Type 1 and 2 lobules remain. According to the Breast Cancer Prevention Institute, a recent study found that, “2 or more abortions increased risk for breast cancer by 610% and family history of breast and ovarian cancer increased risk by 325%.”(1),(2)
Research: Abortion Increases Cancer Risk
In 2023, a new breast cancer risk screening model was developed by researchers in southeast China.(4) It looked at many factors, including menopausal status, age at first live birth, number of births, breastfeeding, number of abortions, and family history of breast and ovarian cancers, among others, as potential risk factors.
According to the Breast Cancer Prevention Institute, the study found that, “2 or more abortions increased risk for breast cancer by 610% and family history of breast and ovarian cancer increased risk by 325%.” In the results discussion section, the study stated, “We confirmed that age, age at menarche, age at first live birth, number of births, abortions, family history of breast and ovarian cancer, and prior breast surgery are strong risk predictors for breast cancer. In addition, the performance of the model established in this study was better than models based on CKB score, Gail score, and Tyrer-Cuzick score.”
The Gail Risk model is "commonly used in the U.S. to estimate a woman’s risk for developing breast cancer and does not include an abortion history or contraceptive use. An abortion history is common in China due to the decades long ‘One Child Policy’ which included forced abortion.”
“Chinese researchers found that the Gail model was not a good risk model for Chinese women, so they decided to make one for their own population. They found induced abortion was a Chinese woman’s most impactful risk. In the U.S., about 1 in 4 women have had an abortion and 10% have had 2 abortions, so it is a prevalent risk on our country as well.(5) Hopefully one day all risk models will include abortion as a recognized and impactful risk.”(6)
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Sources
(1) Lanfranchi, Angela, MD, FACS. “Report: October 2023.” Breast Cancer Prevention Intitute, October 2023.
(2) Zou, Shuqing, et al. “Genetic and Lifestyle Factors for Breast Cancer Risk Assessment in Southeast China.” Cancer Medicine, vol. 12, no. 14, 2 June 2023, pp. 15504-15514. https://doi.org/10.1002/cam4.6198. Accessed 25 August 2025.
(3) “The Biologic Cause of the Abortion Breast Cancer Link: The Physiology of the Breast.” Breast Cancer Prevention Institute, revised May 2004, https://www.bcpinstitute.org/uploads/1/1/5/1/115111905/bcpi-factsht-physiology2004.pdf. Accessed 8 April 2025.
(4) Zou, Shuqing, et al. “Genetic and Lifestyle Factors for Breast Cancer Risk Assessment in Southeast China.” Cancer Medicine, vol. 12, no. 14, 2 June 2023, pp. 15504-15514. https://doi.org/10.1002/cam4.6198. Accessed 25 August 2025.
(5) Jones, Rachel K. and Jenna Jerman. “Population Group Abortion Rates and Lifetime Incidence of Abortion: United States, 2008-2014.” The American Journal of Public Health, vol. 107, no. 12, 8 November 2017, pp. 1904-1909. https://doi.org/10.2105/ajph.2017.304042. Accessed 25 August 2025.
(6) Lanfranchi, Angela, MD, FACS. “Report: October 2023.” Breast Cancer Prevention Intitute, October 2023.