What is the main topic of the conversation?

M: Hi, Alison.
W: Oh, hi, Peter. Have you been training hard for Sunday’s run for breast cancer?
M: You bet. I have been running three times a week for over an hour each time. It’s great. I can’t believe I’ve gotten to this point so quickly! Only six months ago I would run for five minutes and almost collapse in exhaustion.
W: I hear you. I decided to run in this marathon because I needed a motivator to get myself back into shape. During my pregnancy I gained a whopping eighty pounds, and I’m still trying to trim down. Also, I totally believe in the cause. I know so many people who have been touched by the disease.
M: Wow! Eighty pounds! That’s nuts! Did you have triplets?
W: No, just a big little boy. He was born 9 pounds, 5 ounces. Hey, Peter, what inspired you to want to run this weekend?
M: Well, a bunch of my running buddies thought it would be a great idea. We all started running at the same time and when we heard that one of the guys’ mothers was diagnosed with cancer, we thought the marathon was something positive we could do as a group. It should be a lot of fun, and I’ve been collecting lots of sponsors from school. So I’ll hopefully make tons of money for the cause.
W: That’s so cool. Hey, I’ve got to dash. I’ll see you at the finish line on Sunday.