Nenemiles. I am sure you are now determined to seek a second opinion, after all the other replies, but I also have to have my say.
please please have other tests soon. When it is your life you really need to take charge. I also have dense cyst filled breasts. I only learnt from having breast cancer that they can be very difficult to read on mammogram and ultrasound. I had one biopsy that was benign, so it cost a little money and a bit of time to find out, but it was worth it.
The next one in the other breast was cancer.
Dont stop pushing for answers until you are satisfied.
I send you warm thoughts and sisterly prods in the back to investigate further.