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updated 4/21/2015 11:45:11 AM ET 2015-04-21T15:45:11

PHILADELPHIA — The number of breast cancer cases diagnosed each year in the United States could rise 50 percent during the next 15 years, a new study suggests.

By 2030, there will be 441,000 new breast cancers diagnosed yearly in U.S. women ages 30 to 84, according to the study's estimates. That's up from 283,000 breast cancer cases in 2011.

 Part of the reason for the rise in breast cancer cases is simply that the population is growing, so there will be more cases, said study researcher Philip Rosenberg, a senior investigator in the division of cancer epidemiology and genetics at the National Cancer Institute (NCI), who presented the findings here today at the meeting of the American Association for Cancer Research.

People are also living longer, and cancer risk increases with age. Finally, different generations of women may also have differences in lifestyle factors that could affect the risk of breast cancer — for example, women in today's older generations may have been less likely to have breastfed their children, Rosenberg said.

"Managing this clinical burden will present a huge challenge," Rosenberg said.

The new estimates include cases of both invasive breast cancer and "in situ" conditions (which are considered by some to be the earliest form of breast cancer, but by others to be a precancerous state). In situ cases are detected almost entirely through screening, but in the new study, the researchers assumed that levels of screening would remain about the same as they are now.

The researchers predict there will be more breast cancers diagnosed in older women : Breast cancers in women ages 70 to 84 accounted for 24 percent of all cases in 2011, but will account for 35 percent of cases in 2030. In contrast, the proportion of breast cancers in women ages 50 to 69 is expected to decrease from 55 percent to 44 percent.

In addition, the proportion of in situ cases that are fueled by the hormone estrogen (known as ER-positive breast cancer) will increase — such cases accounted for 19 percent of all in situ cases in 2011, but that number will be 29 percent in 2030, according to the study. [ 6 Foods That May Affect Breast Cancer Risk ]

A silver lining of the findings is that the study estimates there will be fewer breast tumors that are not fueled by estrogen, which are among the most difficult-to-treat types of breast cancer, Rosenberg said. The proportion of these "ER-negative" breast cancers is expected to decrease from 17 percent in 2011 to 9 percent in 2030.

The reason for this decrease is not known, but the researchers speculate that it might be due to an increase in women breastfeeding their children, and also an increase in women delaying their first pregnancy. A younger age at first pregnancy, and not breastfeeding have both been linked with an increased risk of ER-negative breast cancer, the researchers said. Knowing more about why ER-negative breast cancers are declining may provide researchers with clues about how to prevent this type of breast cancer, Rosenberg said.

To come up with the new estimates, the researchers analyzed data from the NCI and took into account population projections from the U.S. Census Bureau. They then used a mathematical model to make their predications.

© 2012 LiveScience.com. All rights reserved.

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