This article is from the Static Electromagnetic Fields and Cancer FAQ, by John Moulder email@example.com and the Medical College of Wisconsin with numerous contributions by others.
When epidemiological evidence for a causal relationship is weak to non-
existent, as in the case of static magnetic fields and cancer,
laboratory studies would have to provide very strong evidence for
carcinogenicity in order to tip the balance.
Laboratory evidence that static magnetic fields might be carcinogenic
would be evidence that these fields directly damage the genetic material
of cells (genotoxicity) or evidence that they increase the chance that a
genotoxin would cause cancer (epigenetic activity).