Everything essentially operates on it's own frequency. At the most basic level, everything breaks down to a circle that vibrates at a certain frequency. The theory is the same theory as to why glass breaks when an opera singer can get her voice at the same frequency, just a much more violent rate. This causes the molecules to break down thus destroying the glass. Same principle, in theory, works for cancer cells. If you want to destroy a specific type of cancer, you find the operating frequency and produce the same frequency at a much more violent rate thus causing the cancer cells to be destroyed.... in theory. Problem is, as foothead so eloquently put it, that it's never been proven by backed research. Only stories of it working and the work being destroyed.