By Lynne Adkins

PHILADELPHIA (CBS) - A look at more than 30 years worth of breast cancer statistics shows a startling finding for young women.

Analysis of national data between 1976 and 2009 shows that breast cancer rates are steadily rising in women ages 20 to 39.

Dr. Mary Daly, Chair of the Department of Clinical Genetics at Fox Chase Cancer Center, says the disease is also being diagnosed at a later stage — after it has spread to other organs. She speculates this could prompt a change in screening habits.

“There’s been a lot of debate in this country about mammography screening in younger women, so if in fact these younger women are presenting with more metastatic disease, that would make you rethink screening in these younger women maybe we should go back to being more aggressive.”

Dr. Daly speculates on some of the reasons:

“Women are waiting longer to have their first child, and we know that that is a risk factor for breast cancer. Another thing women in that younger age range are doing more and more is oral contraceptives for longer periods of time and there’s some data to suggest that there may be increase risk.”