What Causes Visibility Of White Circle Behind The Nipple In A Mammogram?

I WAS GETTING A MAMAGRAM 2 WEEKS AGO AND BEHIND THE NIPPLE WAS A WHITE CIRCLE BEHIND AND SOME WHITE LINES GOING UP TOWARD CHEST AND ARM PIT.WENT FOR A2ND MAMAGRAM SHOWED THE SAME THING ALSO WENT FOR ULTRA SOUND AND SHOWED THE WHIT CIRCLE AND THE FIME LINES IN THE LAFT BREAST THEY WANTED TO DO MRI AND BYOPSI BUT MY INS WONT COVER IT COULD IT BE CANCER