She was 25 years old and pregnant with her first child—the picture of health, happiness, and the potential of life. But Nicole Davis had no idea that she’d developed a relentless form of cancer that was, in a cruel twist, aggravated by her pregnancy.
Of the roughly 250,000 women diagnosed with breast cancer each year in the United States, most are well over 50. Only five percent of new cases are in women under 40, according to the American Cancer Society, and just 2.4 percent are in women under 35, according to the National Cancer Institute. Even so, that tiny group is growing slightly. According to NCI data, the number of women diagnosed in their 20s rose by an average of nearly three percent a year between 2000 and 2008. This increase has happened amid a steady spread of breast cancer throughout the world. The incidence of the disease in the United States has jumped from roughly 105 of 100,000 women diagnosed in 1975 to 125 of 100,000 in 2005, NCI data show. And although breast cancer was once an affliction of the industrialized world, recent years have seen a marked upswing of diagnoses in developing countries.
The increase is partially a result of additional screening via mammograms, improved ability to diagnose cancer earlier, and the fact that more women are living longer. But researchers also cite a number of lifestyle factors: Obesity raises breast cancer risk in post-menopausal women, for instance. And the longer women wait to start families—and the fewer children they have—the greater their likelihood of getting breast cancer. (The more children a woman has before the age of 30, the less likely she is to develop breast cancer.)
But there is a cruel twist. Pregnancy actually elevates a woman’s risk of developing breast cancer temporarily. “The interaction between pregnancy and subsequent risk of breast cancer is very complex,” says Dr. Virginia Borges, an associate professor at the University of Colorado School of Medicine who specializes in young women’s breast cancer. “We know that any pregnancy at any age causes a period of time when that woman is at increased risk of getting diagnosed with breast cancer. How long that period lasts depends on age: If she’s under 25, she’ll be at a small increased risk of getting breast cancer, and then it will go away and she’ll be protected by virtue of having had a baby. If a woman is over 30, and certainly over 35, that risk is elevated. We’re not sure why.”
Twenty-five thousand cases of breast cancer were diagnosed in American women under the age of 45 in 2009, with 30 to 40 percent, Borges says, diagnosed in association with a recent pregnancy. Around 70 percent of all breast cancers are hormone-positive, which means estrogen and/or progesterone feed them. So in pregnant women, the hormones critical to a fetus’ growth can also fuel cancer. As Dr. Otis Brawley, an oncologist and chief medical officer of the American Cancer Society, puts it, the estrogen surge that comes with pregnancy is like “putting a tumor on caffeine.”