A method of screening for breast cancer, comprising: testing a plurality of asymptomatic women by measuring at least one electrical impedance characteristic on at least one breast, said asymptomatic woman being classified as belonging to a first group having a first risk factor for breast cancer; and re-classifying some of the women as belonging to a second group having a second risk factor greater than the first risk factor, based on the at least one impedance characteristic, wherein the second group has a risk factor of at least twice that of the first group, but less than 15 times that of the first group; and wherein fewer than 60% of those in the first group that have breast cancer are reclassified into the second group.