By Kay Quinn, KSDK-TV, September 6, 2007

Age, genes and having a close relative who has had breast cancer are some of the risk factors many women have already heard about.

Now, a local doctor''s research study shows two more risk factors should be added to the list: having dense breasts and/or high levels of estrogen after menopause.

Until now, it''s likely the person reading your mammogram is the only person who knew whether you have dense breasts or not.

The more ductal tissue, the denser your breasts are. And because fatty tissue can''t turn into cancer, the denser your breasts are, the higher your risk of developing breast cancer.

"My very first mammogram I remember that very clearly, them saying to me, oh, you have really dense breasts," recalls Missy Fish.

Not only did Fish have dense breasts, she''s also had breast cancer -- twice. The first time it was diagnosed by sheer chance.

She was 39 and working for a cancer prevention organization. She decided to have a mammogram just to see what it was like. That mammogram showed cancer.

"I was kind of like, ''Whoa, I was just trying to have an experience, not have this experience,''" Fish said.

Armed with the information that she also had dense breasts, Fish said she wasn''t surprised when cancer was found in the other breast in 2005.

"Maybe I''m weird, but I always believed I was going to get it on the other side and I don''t know why. I wasn''t particularly frightened of it because I knew I was being monitored so carefully that it wasn''t going to come from out of nowhere," Fish said.

"One of the interesting questions that still hasn''t been solved is just how does breast density increase risk of breast cancer," said Dr. Graham Colditz, associate director of prevention and control at the Siteman Cancer Center.

Colditz is one of the authors of the study. He said it found not just breast density, but another factor - higher levels of estrogen after menopause - can greatly influence whether a woman will get breast cancer.

"I think we are making progress and these are two of the risk factors that really tie in, in post menopausal women," Colditz said.

Right now, there''s no standard screening test to check estrogen levels after menopause, so it''s difficult to know which women falls into this category.

Dense breasts are easier to identify thanks to mammography and appear to be a powerful risk when compared to the other risks factors.

For example, it''s a stronger risk factor than age or family history. Women with them have four times the risk of developing breast cancer than women without.

Colditz encourages women to ask whether they have dense breasts when they have their next mammogram, and to talk with their doctors about prevention strategies that can lower their risks.

"We know that increasing physical activity after menopause will lower risk of breast cancer, losing weight after menopause will lower risk of breast cancer," Colditz said.

Fish hopes the finding will lead more women to learn about their breast health.

"If you''re told that, I would say insist on a digital mammogram and if they keep coming back and asking for additional views then that means they''re having a hard time reading your mammogram," Fish said.

Ultrasound and MRI images may also be useful to help diagnose suspicious lumps in women with dense breasts.

Talk with your doctor about your risks and about the breast screening that''s best for you.