(Wearing a towel wrap, and skipping that damned nurse's uniform)
Sweetie, I am a nurse, and have seen countless women with these lumps, and all the fears that come with them. I still don't know how I would react if it were me.
You didn't say how old your wife is, but please know that breast cancer is very rare in young women, while benign cysts are common at EVERY age.
But, go to the doctor, and insist on a thorough exam, no matter what her age is, AND a mammogram (ouch! sigh...) maybe an ultrasound, and if there is any doubt, requests a fine needle aspiration. A good surgeon does it without an real scars, and the answer is pretty final.
HUGS
Please tell her to try not to worry too much until the answer comes.

WW

__________________
"I wondered, am I a lesbian, am I straight, or bisexual? Then I realized that I am just a slut.
So where's MY parade?"

---Margaret Cho