-- It took seven years of annual mammograms and a cancer diagnosis for Amy Colton to learn something her doctors had realized from the beginning: Her breast tissue is so dense that it could have masked tumors on earlier exams.

"I requested a copy of the report sent from my radiologist to my primary care physician, and every single one said, `Patient has extremely dense breast tissue,'" the registered labor and delivery nurse said. "I was really outraged that I didn't know this."

About 40 percent of women over 40 have breast tissue dense enough to mask or mimic cancers on mammograms, but many of them don't know it. 

Mammogram providers in California will be required to notify those patients, and suggest that they discuss additional screenings with their doctors based on their individual risk factors, if Gov. Jerry Brown signs a bill that the Legislature passed this month