I am 60 years old with no family history of breast cancer and in good health otherwise. I had just had a mamogram in July which was fine and then around December found this very small knot under my arm pit. I had it checked today and my doctor said that I had felt the largest one and that there was a string of three. She examined my breast and found a mass. She is sending me for a diagnostic mamogram. What is that? And she is sending me to a doctor that does biopsies.