Breast cancer is one of the most common cancers among women in the United States. While all women are at risk for developing breast cancer some time in their life, certain factors have been linked to an increased chance of having the disease. Lifestyle choices such as smoking, drinking, lack of exercise and poor diet can be changed. However, other factors like a person’s age, race, genetics, or family history can’t be changed—no more than we can control our size at birth, which has now also been linked to an increase in breast cancer risk.
Researchers from the London School of Hygiene and Tropical Medicine compared the risk of getting breast cancer with birth size by reanalyzing the results of 32 studies, published and unpublished, which included more than 22,000 cases of breast cancer among more than 600,000 women. For accuracy, the scientists used only birth measurement data from official birth records and parent recall. They found that women who weighed 8.8 pounds or more at birth had a 12 percent increase in breast cancer risk compared to women weighing 6.6 to 7.69 pounds. Head circumferences of 13.7 inches or more boosted the risk 11 percent, compared to those whose head circumference was 12.9 inches. But birth length appeared to be the strongest independent predictor. Women who were 20 inches in length at birth had a 17 percent increased risk compared to those who were 19.29 inches.
One explanation for the connection could be high maternal levels of an estrogen hormone called estradiol may somehow change the programming of the breast, making it more vulnerable to cancer, says the study’s lead author Isabel dos Santos Silva, MD, PhD, professor of epidemiology at the London School of Hygiene and Tropical Medicine. Other growth hormones or even overactive stem cells could play a role. “Little is known on how the prenatal environment may affect breast cancer risk later in life,” she said. “Further research is needed to unravel the biological mechanisms underlying the birth size-breast cancer association.”
“We are facing now a new reality: that breast cancer has its origins several decades before its clinical appearance,” said Dr. Dimitrios Trichopoulos, the Vincent L. Gregory Professor of Cancer Prevention at Harvard University School of Public Health Department of Epidemiology and author of an accompanying journal editorial. “Recognition of early life influences are critical in the etiology of breast cancer and helps to explain why several adult life primary prevention practices—as distinct to secondary prevention ones focusing on early detection—have been of limited effectiveness.”
Debbie Saslow, director of breast and gynecologic cancer at the American Cancer Society said women should not be concerned, no matter their birth size. “There is nothing that women should do differently to try to have smaller babies, or women who were born with a longer length or larger head circumference should do anything differently when they grow up or get screened differently, or consider themselves at high risk—it’s really just a research issue,” she said. “There’s good evidence for these findings, but there is really no clinical relevance for them,” she said. “It’s just one more piece of the puzzle that someday will help the research community better understand the multiple, interplaying causes of breast cancer.”
According to the American Cancer Society, the chance of a women having invasive breast cancer at some point in her life is about 1 in 8. It is estimated that about 182,460 women in the United States will be found to have invasive breast cancer in 2008 and 40,480 will die from the disease.
The study was published in the September 30 online edition of PLos Medicine.
