It's impossible to speculate over the internet ... things like this need to be seen to be properly evaluated. I will say that cancer doesn't spread in the way you describe. I would certainly make an appointment with your Primary Care Physician to have this checked out. He/She can do a clinical breast exam and no doubt tell you what is causing your problem. Regards ....
I'm not clear if you're describing a bump on your breast or in your breast but, either way, I would call your doctor anytime you notice any unusual changes in your breast appearance or if you feel something changing. At the very least, call your MD's office and just describe your symptoms and see how soon they'd want to see you or if they can tell you it's nothing to be concerned about. Take care.