I'me very disappointed that this information is just now being researched.  As a woman with dense breasts, its always been obvious to me that mammograms would not be as effective for me as for the women with breast tissue that is not dense.  It just makes sense.  An xray can't penetrate that much tissue...and the dense tissue looks very much like cancer on an xray. Insurance companies will lobby against additional testing for women like me because we are at higher risk of cancer (according to this research), and we need expensive testing to be sure we are cancer free.  In fact, I wouldn't be surprised if the insurance companies soon deem dense breasts as a pre-existing condition.