The teaching point is that the initial mammogram was very compelling on the very first image. It's a daily dilemma when you are confronted with a normal ultrasound but your index of suspicion is high on the mammogram. The solution is to get up and ultrasound the patient in real-time and convince yourself that the study is in fact "normal" Do not simply accept "normal" static images if you are convinced a lesion is present.

Second point: just because a lesion does not change with time, is no guarantee it is not malignant.