They say that it is the pressing down on the breast that can also spread it. There is thermo screening that you can do which is also done. That is a machine that can show up breast tumors. But these are not 100%. I have never had a mammogram until I was diagnosed that I had breast cancer. But after alternative treatments my breast mammogram is all clear. Sometimes you just have to know for sure.I also did thermo screening during my cancer treatments.