Hello and welcome to MedHelp's forums. We are glad you are working with your doctor and encourage you to continue to do so. I know this is a scary time but please know that things can be suspicious and turn out to not be cancer. This happens on a regular basis. And if it is cancer, diagnosing it as soon as possible and beginning treatment is the best way to overcome it. So, you are on the right track for having the best outcome for yourself either way. Did your mother have breast cancer? Hypoechoic means that the mass reflects few of the Ultrasound waves that are directed at it. It is a way to find out tissues which appear different from the surroundings and therefore are probably "suspicious". A hypoecoic lesion could be either a cyst or a benign tumor or a malignant tumor. A biopsy is required to determine what is going on. While I know you are scared, please know that this could also easily be benign lesions. BiRad4 basically means that they need to do a biopsy to determine status.
Here's an article to review. Please, again. Do not worry until you have to worry but do follow up with your doctor. If your mom had breast cancer, that puts you at higher risk and you should express this to your doctor.
Please let us know what you think about this information and how you are doing.