Diagnosis of metastatic breast cancer in women younger than 40 has increased 2% a year, every year, from 1976 to 2009, according to a study published Tuesday in the Journal of the American Medical Association. The increase was seen in women aged 25 to 39 of all races and ethnicities, living in both rural and urban areas in the United States. It's a devastating diagnosis, particularly because a woman younger than 40 who is diagnosed with breast cancer is more likely to have an aggressive form of the disease and face lower survival rates. But for perspective, the overall population of women who are affected still remains small. "If you project these data out to the number of people in the U.S., there were about 250 cases per year ... in 1976 and that's now risen to 850 cases of breast cancer per year," said Dr. Rebecca Johnson, the study's lead author and medical director of the Adolescent and Young Adult Oncology program at Seattle Children's Hospital. Those numbers, she says, refer to metastatic breast cancer in women younger than 40. The rise, she says, was "really concerning." Johnson is a breast cancer survivor. She found a lump in her breast and was diagnosed with the disease when she was 27. It was not metastatic. In previous research, she found that a woman younger than 40 had a 1 in 173 chance of developing breast cancer. For this study, she wanted to look specifically at advanced breast cancer within that same population. "Along with my colleague, Dr. Archie Bleyer, a couple of years ago, we just wanted to ask the question, how common is this? Because once I was diagnosed, I had friends and friends of friends getting diagnosed and I didn't know if this was happening more or if I was hearing about it more," she says. Johnson and her team used three U.S. Surveillance, Epidemiology, and End Results (SEER) databases of the National Cancer Institute to obtain data about breast cancer incidence from 1973 to 2009, 1992 to 2009, and 2000 to 2009. They chose 1976 as their starting year. Not only did they find an increase in incidence of metastatic breast cancer in women younger than 40, the team also calculated that the average age of diagnosis was 34.3 years of age in women aged 25 to 39. "From a cancer point of view, it is an important study because it suggests an early signal that there's a significant increase, a sustained increase over a prolonged period of time," said Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society, who was not affiliated with the study. "There's a suggestion this rate is accelerating and it could have a much greater impact so it's important we ... continue to monitor this, we try to understand what its influences are." There is no solid explanation for what's driving the increased incidence, but Johnson and her team suggest there's likely more than one cause. Yet neither she or Lichtenfeld believe the study's findings should change current screening guidelines for breast cancer. "If there is an action item, at this time it's awareness: Breast cancer can happen (in younger women) and if it gets to be metastatic by the time it's diagnosed, that's a problem," said Johnson. Yet while the rate of breast cancer incidence in young women has increased, Johnson and her team found that mortality rates over the last 30 years have been stable. "It's great, except it's not great - the five-year survival rate used to be 15%, and now it's 30%. So that's something to be thankful for, but it's still very bad," she said. "If women could be diagnosed earlier (before the cancer spreads), then each individual woman that that happens to stands to do a whole lot better, stands a better chance of living." Lichtenfeld agreed. "This study reinforced the message, know your body better than anyone else does," he said. "If there is a lump on the breast ... swelling in the breast, discharge from the nipple, redness in the skin of the breast, or unexplained pain in the breast, see your doctor."