This is something I have read in dozens of books on spirituality and spiritual healing. For instance, if you look up anything on the chakra system, you’ll find information like this. Our heart chakra rules the chest/breast area and these are some issues that come up in that area. There’s a ton of info out there if you’re interested, both online and in books by spiritual teachers. As you can imagine, there’s no “proof” for it — just like there’s no proof that we have souls or an afterlife or anything like that. It’s just something I’ve read about that resonates with me. My own experiences tell me it’s true (for me).