More women are getting the word that they may have breasts too dense for mammograms to give a good picture. What's not so clear is what to make of that information.

New York this summer became the fourth state to require that women be told if they have dense breasts when they get the results of a mammogram. That's because women whose breast tissue is very dense have a greater risk of developing breast cancer than women whose breasts contain more fatty tissue. Plus, it can be harder for mammograms to spot a possible tumor.

Monday, scientists reported a bit of good news about yet another question: Do denser breasts also signal a worse chance of survival? A National Cancer Institute study tracked more than 9,000 breast cancer patients and concluded those with very dense breasts were no more likely to die than similar patients whose breasts weren't as dense.

"It's definitely reassuring," said NCI lead researcher Dr. Gretchen Gierach, who reported the results in the Journal of the National Cancer Institute.