does that happen on the outside or inside of the chest? If it's outside, think that's just some skin porblem. However if it's inside, I guess it's better for you to go and see a doctor.
In fact, it is possible for guys to have breast cancer too. First of all, try to observe if the lump grows. Second, check if it feels hard. Another point is, does that occur in both side of your chest. IF it occurs in both side, it'd be fine as you are undergoing puberty. However, if it only occurs on one side, I'll recommend you to see doctor.