I'm 38 and recently found a lump in my left breast. I found it because it was uncomfortable when I laid on my left side. The surrounding breast tissue is lumpy also, but nothing as large as the one lump. My mammogram and ultrasound were negative. Obviously I'm worried it's cancer but can't understand why it didn't show up on imaging. My doctor and the radiologist felt the lump too.
What are the other possibilities besides cancer?