(USA TODAY by Liz Szabo) At a time when the USA is making progress overall against cancer, a new study suggests a worrisome rise in the number of young women diagnosed with advanced, incurable breast cancer.
The number of American women ages 25 to 39 diagnosed with metastatic breast cancer - which has already spread to other organs by the time it's found - rose about 3.5% a year from 2000 to 2009, according to a study in today's Journal of the American Medical Association.
The trend began in the 1970s, although the most rapid increases occurred in about the last decade, the study says. The study doesn't provide any clues about what might be driving the increase, says study author Rebecca Johnson, a pediatric and adolescent oncologist at Seattle Children's Hospital.
"It is a big increase, and it's accelerating over time, and it's hitting the youngest women," says Johnson, also an oncologist at the University of Washington.
Young women shouldn't be overly alarmed, Johnson says, noting that breast cancer at any stage is not common before age 40.
The number of women in this age range diagnosed with advanced disease rose from about 250 a year in 1976 to about 850 a year in 2009, Johnson says.
The largest increases were in the youngest women, from ages 25 to 34, the study says. There were also slight increases in metastatic diagnoses among women ages 40 to 54, but no increase in older women.
There were an estimated 227,000 breast cancers of all kinds in all American women in 2012, according to the American Cancer Society.
Researchers note that their study needs to confirmed by other researchers before doctors can be sure that rates are really increasing. It could be especially helpful to measure trends in other countries, the authors write in their study.
Studies like this "get your attention," says Len Lichtenfeld, deputy chief medical director at the American Cancer Society, who wasn't involved in the research.
"It may not be a big number today, but you have to wonder, 'Is this a trend that's continuing over time?' Then the numbers start to take on a new meaning."
Increases in any cancer are troubling, he says, because overall cancer deaths of all kinds have fallen about 20% in the past two decades.
Breast cancer incidence rates have generally been stable for the past few years.
Breast cancer diagnoses increased for two decades, due partly to increased screenings. Breast cancer incidence dropped 7% from 2002 to 2003, after millions of women stopped using hormonal therapies, because of a landmark study linking the pills to breast cancer and heart attacks.
Johnson's study looked only at numbers - taken from a National Cancer Institute database - and doesn't provide any explanation for the increase.
It's possible that doctors and younger women are less alert to signs of breast cancer, such as a lump in the breast, because they don't expect to see the disease in anyone that young, Johnson says. Women ages 25 to 39 are also more likely to be uninsured than older women.
Many researchers are concerned that girls today are entering puberty earlier than in the past. Girls who begin menstruating early are usually at a higher risk of breast cancer. But Johnson doesn't know if this trend is really causing an increase in metastatic cancer.
Johnson - who was diagnosed with breast cancer in her 20s - says the cancers in women ages 25 to 39 probably grow very quickly, given that the tumors had already spread to organs such as the bones, brain or liver at the time of diagnosis.
Breast cancer is generally more aggressive in younger women, Johnson says, noting that women in this age group are 40% more likely to die of their disease than postmenopausal women.
Many doctors suspect that breast cancer in young women is a very different disease than in older women, perhaps caused by different risk factors, says Patricia Ganz, who specializes in treating breast cancer in young women at the Jonsson Comprehensive Cancer Center at the University of California-Los Angeles.
Ganz notes that women are at increased risk of breast cancer for five years after giving birth. The huge hormonal fluctuations during pregnancy could fuel some of these cancers.
Women who have their first child after age 35 have a higher risk of breast cancer than if they had never given birth, research shows.
Although doctors have made important advances in treating metastatic breast cancer, and prolonging women's lives, the disease is considered incurable. While 87% of women diagnosed with earlier cancers survive at least five years, only 31% of those with metastatic disease live that long, the study says.
Lichtenfeld of the American Cancer Society says he's concerned about the trend. But he notes the cancer society doesn't recommend routinely screening women ages 25 to 39 for breast cancer, unless they have a special risk factor.
But Lichtenfeld agrees there needs to be more research into metastatic disease in younger women.
"We're left with an observation without an explanation," Lichtenfeld says.
Being diagnosed with a deadly cancer at such a young age is especially tragic, because many of these women are caring for young children who depend on them, Lichtenfeld says.
"It's a terrible situation," Lichtenfeld says. "These women are mothers, wives, members of families. They are caregivers. They're just getting their lives started. That's what makes it so difficult."