Can putting your iPhone in your shirt pocket cause breast cancer?

I'm giving my iPhone 4 to my mom once I get the iPhone 6 when it comes out. At her job, she usually puts the cell phone in her front shirt pocket, pretty much by her breast. Is it possible for a cell phone to cause breast cancer? I had a friend telling me that she knows someone that would put her cellphone in her bra and she got breast cancer from it. Just a little worried about giving my phone to my mom, right now she uses a cheap slide phone she got for about $40.

Maybe, yes. But,
no recorded evidence so far.