Do what your doctor suggests. However, nothing is bullet proof. I have invasive breast cancer. it is very thin - like jelly - it spreads across the breast. I had many mamos, an many ultrasounds, a number of biopsies and MRIs and they MISSED the CANCER. I asked them to do a prophylactic mastectomy - the doctors told me I was being "silly". After the mastectomies, they found Stage 2 Invasive lobular breast cancer.
Nothing is bullet proof. So even mamos, us, biopsies and MRIs can miss it all. Also remember, the mamos you are getting are exposing you to radiation and can also cause cancer as much as they can diagnose cancer. It is a two edged sword.