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The Biology of the Abortion-Breast Cancer Link

July 2012
By: Angela Lanfranchi
There is a cancer-reducing benefit to carrying and delivering a baby. Abortion offers the opposite result—breast cancer probability goes up for women with an abortion in their past. This is linked to the process that breast tissue undergoes during pregnancy.


Years of published research sheds light on the breast maturation process, which accounts for the protective effect of a full-term pregnancy.i During the Middle Ages, only nuns were getting breast cancer. Most nuns were childless, while most other women had early pregnancies. Today, by the 'Gail Risk' model, women who give birth at age 18 have a 50 percent lower risk of breast cancer than women who give birth at age 30.ii It is under the influence of the pheromones hCG and hPL, made by a baby in his mother's womb, that the mother's breast matures from cancer vulnerable Type 1 and 2 lobules (a lobule is a unit of breast tissue comprised of a duct and several milk glands) into cancer resistant Type 4 lobules containing milk. Type 4 lobules later regress to Type 3 after weaning, but retain the genetic changes that make them cancer resistant as well.

During pregnancy breasts enlarge, doubling in volume. Due to the stimulating hormones estrogen and progesterone, the number of lobules increases in preparation for breastfeeding. Most of the maturation needed for resistance to breast cancer does not occur, however, until after 32 weeks of pregnancy. The breast continues to mature, gaining maximum protection at 40 weeks (full-term). This accounts for the recognized risk that any premature delivery before 32 weeks more than doubles breast cancer risk.iii Induced abortion also increases risk in proportion to the length of pregnancy before the abortion occurs.iv In terms of breast cancer risk, the only difference between a premature delivery before 32 weeks and an induced abortion is the condition of the delivered baby, i.e., alive or dead.

Spontaneous abortion (miscarriage) does not increase risk because the mother's breasts do not enlarge with increased numbers of cancer-vulnerable lobules. Her estrogen and progesterone levels are lower than in a normal pregnancy. That's why women who miscarry often report never having felt pregnant.

Graphics obtained from

Three Ways Abortion Increases Breast Cancer Risk

Loss of the Protective Effect of a Full-term Pregnancy
A woman who is pregnant can choose to let the pregnancy go to term, resulting in her having a lower breast cancer risk than if she chooses to end the pregnancy through abortion.

The Independent Risk

A woman who chooses abortion leaves her breasts with more places for cancer to start. She has permanent changes in her breasts caused by the pregnancy hormones, and the baby's pheromones will not result in risk reduction until the pregnancy continues to at least 32 weeks. Her breasts are left with more Type 1 and 2 lobules—where cancers start—than when her pregnancy began.v

Induced Abortion Causes Premature Delivery

Forty-nine studies show that induced abortion causes premature deliveries in subsequent pregnancies. Preterm births are known to more than double breast cancer risk if they occur before 32 weeks gestation. Induced abortion damages not only the mother's health, but risks the well-being of her future children. Pre-maturity is linked, for example, to conditions such as cerebral

Dr. Lanfranchi is a clinical assistant professor of surgery at the Robert Wood Johnson Medical School, co-director of the sanofi-aventis Breast Care Program at the Steeplechase Cancer Center in Somerville, NJ, and co-founder of the Breast Cancer Prevention Institute

i Russo, J., et al. (2001). Cancer risk related to mammary gland structure and development. Microscopy Research and Technique, 52: 204-233; Russo, J., et al. (2001). Mammary gland architecture as a determining factor in the susceptibility of the human breast to cancer. The Breast Journal, 7:278-291.

ii Thorp, J. M., et al. (2001). Long-term physical and psychological health consequences of induced abortion: a review of the evidence. Obstetrical and Gynecological Survey 58:1.

iii Melbye, M., et al. (1999). Preterm delivery and risk of breast cancer. British Journal of Cancer. 80:609-13.

iv Melbye, M., et al. (1997, January 9). Induced Abortion and the Risk of Breast Cancer. New England Journal of Medicine. 336.2:81-85.

v Breast Cancer Prevention Institute. (2007). Reproductive Breast Cancer Risks and Breast Lobule Maturation, [Brochure]. Available at resources.

vi Rooney, B., Calhoun, B. (2003). Induced abortion and risk of later premature births. Journal of American Physicians and Surgeons 8:46-49; Behrman, R., et al. (2006). Preterm Birth: Causes, Consequences, and Prevention. Institute of Medicine. 625, Appendix B, Table 5.

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