Breast exam stuff?

I like my boobs and they've been growing lately (I think due to my bc or antipsychotics) and I find myself holding them pretty often 😂 so im usually checking for any type of lumps or something when Im holding my boobs cause Cancer runs in my family and I've always figured I'd be the one to get it. Anyways I can always feel I guess the fatty tissue or whatever muscle maybe? But my bf was playing with them and make a joke that he thought it was a tumor so how do you know when you find something?