But we're talking about what happens after that GHz RF is absorbed by the tissues/fluids in the body. That becomes much more complex. It's not unlike the laser attack on MEMS microphones or a crystal radio powering a speaker in the audio range after receiving AM RF at 1Mhz.

Realistically we've been beaming our brains for decades now without a glut of brain tumors, but we might just be getting lucky, and if we don't know what to look for it could bite us later.