Hard part in one of my boobs

So my boyfriend and I were cuddling the other day and I didn’t have a shirt or bra on and he grabbed my left boob then my right and said that a part in my left boob felt “hard” not like a lump but I guess not as soft as the right and I felt the same thing kinda I don’t know what the cause of this could be any advice? Breast cancer dose run in my family but I’m afraid to bring it up to my mom and find out something is wrong. I don’t even know how I would bring it up to my mom considering how I found out about it any advice would help.