Breast cancer is the most common form of cancer in women, striking 1 in 7.5 women during their lifetime in America, where the rate is among the highest in the world. Breast cancer is the most fatal cancer for women after lung cancer. The number of cases has significantly increased in America since the early 1970s, when abortion was legalized. Although it is far less common in men, breast cancer can also affect them.
Another study in 1996:
- Animal studies have suggested that estrogen secreted early in pregnancy stimulates the multiplication of immature cells in the breast and that these cells do not mature fully until the end of pregnancy. Theoretically, then, when a woman's pregnancy is cut short through induced abortion, a lot of immature cells remain in the breast that are vulnerable to cancer-causing influences. 
Many factors affect the incidence of breast cancer in any given population of women including:
- lack of having children, or postponing having children until later in life
- diet 
- obesity 
- family history if such a history involves having several generations affected by breast cancer or having many relatives diagnosed with breast cancer at less than 50 years old 
- prolonged uninterrupted exposure to estrogen (e.g. by having an early menarche and late menopause or by having no full-term pregnancies).
- age: increasing age increases the risk that at some point in her life a woman will contract breast cancer, rising from 1 in 231 (0.5% risk) aged under 40 to 1 in 7 at age 90. 
Ways of reducing the risk
Breast self-examination carried out every month, ideally one week after beginning a menstrual period, is a common-sense measure to aid early detection of suspicious changes.  For women over the age of 40, mammogram screenings are another measure that can detect cancer earlier, when it is easier to treat. However, not all medical authorities agree on whether there is any benefit from having annual mammograms below the age of 50. 
- "... childbearing before the age of 35 reduces a woman's breast cancer risk and breast-feeding also helps, said the new study's lead author Karin Michels of Harvard Medical School" 
- The increase in risk of breast cancer due to abortion is explained and supported with numerous citations in our abortion entry.
- Analysis of Studies Suggests Abortion Can Raise Breast Cancer Risk - New York Times - October 12, 1996