Seems that Peter noticed a suspicious lump and had it checked out and removed, and it turned out to be cancerous. He is currently cancer-free but is taking advantage of Breast Cancer Awareness Month this month to get the word out that yes guys have a small amount of breast tissue and can indeed get breast cancer. Rare, but it happens.
CNN tells Peter's story well, and has some good commentary by the man himself such as, "It's just important -- just go get checked out. It's not like you're going to lose your manhood."
I actually had a lump in a pec a couple of years ago and went to get it checked out. It was nothing and it went away by itself but at that time I learned that guys can get breast cancer. I was slightly freaked out when they slammed my meager tit into the mammogram machine but it beats dying, you know?
Anyway, good for Pete for having the balls (and tits) to speak out on this issue. It's no joke.