Can the doctor tell the difference between a breast cyst and a tumor? how?

Ultrasound or Needle: It is very easy to distinguish being a cyst, which is fluid-filled, and a tumor, which is almost-always solid, by performing an ultrasound. Alternatively, a needle aspiration can be done. This sounds worse then it is--it hurts about as much as having your blood drawn. Bottom line: if you find a lump in your breast, see your primary care doctor or gynecologist.