Women who smoke—and especially those who started smoking prior to the birth of their first child—have an increased risk of breast cancer, according to the results of a study published in the Journal of the National Cancer Institute. The study indicates that smoking might actually play a role in the initiation of breast cancer.
Breast cancer is the second leading cause of cancer death in women in the United States. The chance of an individual developing cancer depends on both genetic and non-genetic factors. Non-genetic factors may include diet, or exposure to other substances, including tobacco. The relationship between smoking and breast cancer has been controversial—and studies have produced conflicting results.
In this study, researchers analyzed data from 73,388 women from the American Cancer Society’s Cancer Prevention Study II (CPS-II) Nutrition Cohort. During a median follow-up of 13.8 years, researchers identified 3,721 cases of invasive breast cancer. They found that the rate of new breast cancer cases was 24 percent higher in smokers than nonsmokers and 13 percent higher in former smokers than nonsmokers.
What’s more—the researchers found that the risk of invasive breast cancer was highest among women who began smoking at an earlier age. Compared to nonsmokers, women who started smoking prior to the beginning of menstruation had a 61 percent higher risk of developing breast cancer. Women who began smoking after the initiation of menstruation, but 11 or more years prior to the birth of their first child, had a 45 percent higher risk of developing breast cancer compared to nonsmokers.
The researchers noted that their findings were supported by numerous other cohort studies. In fact, the combined results of nine studies (including this one), indicated that women who started smoking at a younger age had a 12 percent increased risk of breast cancer and those who started smoking before the birth of their first child had a 21 percent increased risk.
The researchers noted that breast tissue is not fully developed until a woman has her first child, which makes it more sensitive to the harmful effects of tobacco. They concluded that it is important to encourage young women to not start smoking. Smoking has been associated with a number of types of cancer, including lung cancer and cancers of the mouth, lips, nose and sinuses, voice box, throat, esophagus, stomach, pancreas, kidney, bladder, uterus, cervix, colon/rectum, and ovary, as well as acute myeloid leukemia.
Gadet MM, Gapstur SM, Sun J, et al. Active Smoking and Breast Cancer Risk: Original Cohort Data and Meta-Analysis. Journal of the National Cancer Institute. Published early online February 28, 2013. doi: 10.1093/jnci/djt023