Dear LK13, Hypoechoic is a description of how a mass or nodule looks on an ultrasound. A solid mass appears on an ultrasound as hypoechoic. The most common type of solid mass seen on an ultrasound is a benign breast tumor (not cancer) called a fibroadenoma. It is possible that over time a fibroadenoma would disappear and it is estimated that in 50% of the cases that may happen in 5 years time. Fibroadenoma's in themselves can be left alone to resolve on there own. The concern is whether or not we are sure a breast nodule is a fibroadenoma. If there is a concern that it may be something more serious biopsy would likely be recommended.