50 GHz is still significantly less energetic than visible light, which is in the hundreds of terahertz. The sun bombards us with a lot of visible light, but you have to get into the blue/violet/ultraviolet region before it's energetic enough (high enough frequency) to cause damage. Barring some strange and previously unknown special biological interaction with a particular radio frequency, radio signals which have lower frequencies and lower intensities than visible light from the sun are not going to cause cancer any more than exposure to red or green light would cause cancer.