Hello, welcome to the forum. Sorry you are having this concern. When is your ultra sound scheduled? A partially circumscribed mass does not mean cancer necessarily. They are doing the ultrasound to get a good view. Were you given a Bi-rad score? This is a scoring system radiologists use for abnormal mammograms. It ranges from 0 t0 6. Circumscribed relates to the contour of the mass and is one of the elements that will cause radiologists to want to take a closer look. A circumscribed mass in mammography is a mass where the contour is clearly defined along at least 75% of its surface. The mass could still be benign. Further investigation is a good thing as it rules out cancer. In the chance that you would have cancer, it allows them to begin treating you for remission. https://www.sciencedirect.com/science/article/pii/S2211568413003872
Please let us know when your ultrasound is and what they say. We'll be thinking of you.