Cell phones cause cancer the headline screamed. Really? I always wondered how this would happen; in other words what mechanism caused cancer from the cell phone. I mean, shouldn't we be worried about the "electromagnetic energy" from the phone??!!
It's the electromagnetic spectrum, stupid! You can't say "electromagnetic energy" as this encompasses a host of radiation types.
Ionizing radiation (gamma, X-rays, K-rays) can cause cellular genetic damage, which the body can and does repair. Your body is naturally radioactive, from carbon, potassium (and other) isotopes. Ionizing radiation does not cause cumulative damage, unless the dose is high, such as exposure to unshielded reactor fuel, atomic bomb blasts, etc. Other radiation, such as Beta and Alpha particles, can be very hazardous if ingested if inhaled. Cell phones do not produce ionizing radiation.
Magnetic radiation is similar to the earth's magnetic field. There's evidence that intense magnetic fields - such as near a dynamo or a Tokamak - cause a rare brain cancer: astrocytoma. The earth's magnetic field (800 milligauss) dwarfs magnetic fields encountered by the public (the voice coil in a cell phone).
Electric radiation are fields encountered in proximity to power lines, thunderstorms, and nerve conduction in the body. That said, exposure to almost any electric field encountered (the power supply in a cell phone) is insignificant compared to that within one's own body's nervous system.
Microwave radiation (RF, radio frequency) is used by cell phones to communicate. Exposure to high levels of microwave radiation generally produce only "thermal effects". There is some limited evidence that exposure to high levels of microwaves can denature proteins. Again, at levels way, way, way, way above anything encountered from a cell phone.
So we see there's no mechanism for a cell phone to cause/contribute to cancer. Epidemiological studies (USA, Denmark) have shown no cancer linked to cell phone use. Maybe their car is causing the brain tumor - plasticizers leaching from vinyl interiors, exposure to benzene when pumping gas, auto exhaust is a known carcinogen.
Or perhaps there's a certain % of the population that will get a brain tumor. A high % also have cell phones. It's a high probability that a person with a brain tumor uses a cell phone. You might as well say wearing glasses or contact lenses causes brain tumors. The link is circumstantial, not causative.