A mechanism for EM fields causing cancer has been found.
Cells undergo damage all the time, there is natural radiation, oxidation, chemical poisons- all cells in all animals are under attack constantly.
However, if a cell is about to divide it is imperative that any genetic damage must be patched up before division occurs- otherwise the DNA can get further destroyed during this process. There exist known mechanisms that put a halt on division until repair has completed.
However, it has been found that a large magnetic field somehow allows cells to divide even when it has unrepaired damage by radiation still present. This can then trigger cancer.
However, it currently looks like the magnetic field to cause this effect is much greater than people are likely to face in their everyday lives, research in this area continues. | 
