There may have been a rising rate of advanced breast cancer occurrence among younger women, ages 25 to 39, over the last 34 years, according to a new report published in the Journal of the American Medical Association. The study estimates that advanced cases rose from 1.53 per 100,000 women in 1976 to 2.9 per 100,000 younger women in 2009. The study analyzed data from the National Cancer Institute’s SEER program, which collects statistics on 28 percent of the U.S. population. The basis of the study is information from 936,497 women who had breast cancer from 1976 to 2009. Of those, 53,502 were 25 to 39 years old, including 3,438 with advanced breast cancer. The study determined that younger women were the only ones in whom metastatic disease had apparently increased. The researchers say the increase is troubling because it involved cancer that had already spread to vital organs by the time of diagnosis. However, they say more analysis is needed, as they do not know the cause of the apparent increase. One researcher also pointed to a lack of evidence that breast cancer screening helps younger, asymptomatic women with an average risk for the disease.