The device is so easy and safe to operate it could be installed in GP surgeries or even used at home.
Instead of producing X-rays, the new scanner emits radio waves similar to those generated by a mobile phone handset.
A tumour can be detected within a second from differences in the way diseased and healthy tissue react to the signals.
The device, consisting of a cup that fits over the breast, is as small and portable as a lunchbox. It produces clear images that can be displayed on a laptop screen. Tumours or other abnormalities show up in red.
Experts believe it will be far better than a conventional mammogram at finding breast cancer in younger women. Because tumours are harder to spot in dense young breasts, the detection rate for women under the age of 50 can be as low as 60%.
Malignant breast tissue is more sensitive to electric fields generated by radio waves than healthy tissue. The scanner uses this property to generate images at the rate of 30 a second.