Abnormal tissue

I have a painful lump about the size of a kidney bean below my left nipple. I found it in a BSE after a physical by my doctor. I had a diagnostic mammogram which they said was clear but they want me to have an ultrasound as there was abnormal tissue present and a palpable lump.  What could this all mean?
Thanks for your answers.....

[CCF-RN,MSN-rf]

Dear heatherjean:  The doctors probably want to do an ultrasound to determine if this lump is fluid filled.  Cysts often appear quickly and can be painful.  They may also be cyclical.  Caffeine can also contribute to their growth.  If this is cystic, then it can be aspirated to reduce pain.  Otherwise, there is no reason to remove a cyst.  If it is not cystic, then further evaluation may be necessary.