CHICAGO (AP) — Advanced breast cancer has increased slightly among young women, a 34-year analysis suggests. The disease is still uncommon among women younger than 40, and the small change has experts scratching their heads about possible reasons.
The results are potentially worrisome because young women's tumors tend to be more aggressive than older women's, and they're much less likely to get routine screening for the disease.
Still, that doesn't explain why there'd be an increase in advanced cases and the researchers and other experts say more work is needed to find answers.
It's likely that the increase has more than one cause, said Dr. Rebecca Johnson, the study's lead author and medical director of a teen and young adult cancer program at Seattle Children's Hospital.
"The change might be due to some sort of modifiable risk factor, like a lifestyle change" or exposure to some sort of cancer-linked substance, she said.
Johnson said the results translate to about 250 advanced cases diagnosed in women younger than 40 in the mid-1970s versus more than 800 in 2009. During those years, the number of women nationwide in that age range went from about 22 million to closer to 30 million — an increase that explains part of the study trend "but definitely not all of it," Johnson said.
Other experts said women delaying pregnancy might be a factor, partly because getting pregnant at an older age might cause an already growing tumor to spread more quickly in response to pregnancy hormones.
Obesity and having at least a drink or two daily have both been linked with breast cancer but research is inconclusive on other possible risk factors, including tobacco and chemicals in the environment. Whether any of these explains the slight increase in advanced disease in young women is unknown.