I had a negative mammo but had an ultrasound due to dense breasts. doctor saw benign cysts and wasn't concerned. should i be? will they go away?

Sounds like: You have a good doctor managing the imaging well without jumping to the mr. Cysts are common. Your doc and the radiologists will have a plan to re-image/u/s or even aspirate for cytology. Hand held transducers can be somewhat hard to reproduce exactly, but they have seen the cycsts, their size, and what the cavities look like. This is sufficient.

No: Lots of people get cysts. Sometimes they go away. Sometimes try get bigger and need to be drained but benign means not cancer.

Don't worry!: Cysts are common and they may come and go, or get bigger and smaller with your menstrual cycle. However, if you have a lump that is not changing with your periods, or is getting larger over time, then go back to your doctor! mammograms aren't as good in women with dense breasts, so any breast abnormalities need to be evaluated carefully by a clinical exam, imaging, and maybe biopsy.