It sounds like you are getting excellent screening. I had the benefit of excellent screening, too, due to the fact that I have a family history of BC, as well as dense breasts. If you have been told you have dense breasts, then it makes the mammograms and possibly even ultrasounds harder to read. Eventually, the radiologist recommended an MRI to supplement my mammogram and ultrasound, which did detect a small tumor, and I had a lumpectomy earlier this week. Due to careful screening, they caught it early. For years, though, my screening turned up nothing other than benign cysts. Hopefully, yours is just a cyst. Be grateful for careful screening, because usually it's nothing, but on the off chance, they do find something it is best to catch it early. I wish you well.