Hi, I am a 4-year breast cancer survivor. On my last mammogram I was called back for an ultrasound and was told that they had found new breast tissue

I would be suspicious of that as well. I don't know how old you are, but if you take estrogen, new tissue can appear on a mammogram. If you are not undergoing hormone replacement therapy, then a new area of tissue should be regarded with suspicion. I would ask for a biopsy. When you lose weight, the breast may be smaller and look more condensed on a mammogram, but a new area of tissue should not develop. What I do when there's an area of abnormality on a mammogram is solve it on the mammogram by doing additional views. I then go to ultrasound to see if I can tell if the area of concern is normal breast tissue or a cyst or a mass.
Tonight we have talked a lot about tests—tests performed within the hospital as well as your own breast exams and your doctor's exams. If you find a lump in your breast that persists, even if the mammogram and ultrasound are read as normal, it's important to follow and evaluate the lump. We do have a tendency to favor technology over something as simple as your own breast examination. Of course, you want to be completely reassured by the normal test report, but again, about 20 percent of women are diagnosed with breast cancer based on a palpable or visible abnormality that is not seen by mammography. It's important to take this a step further with ultrasound or the other tests described above by Dr. Brennecke.