I had exactly the same experience. Fortunately I had a good radiologist who didn't like what she saw on the mammogram, so ordered a diagnostic mammogram, plus ultra-sound. She showed me where I had suspicious calcifications on those tests, then ordered a needle biopsy. She said that 80% of needle biopsies turn out to be benign, but mine was malignant. Turned out to be a 2mm invasive lobular carcinoma. I am very lucky it was found so early. I think one reason they call regular mammograms "screening mammograms" is not that they always find cancer right away (which some do), but that they give hints to the radiologist about possible cancer, which should be further investigated.