Radiation causes cancer; does being a firefighter also cause cancer? Causation is never that simple, as this 68 page opinion and dissent demonstrate. In this case, a firefighter gets brain cancer and claims it was related to his employment and the hazardous chemicals to which he was exposed on the job. The central issue on appeal is what evidence the fire district must present to prove that being a firefighter did not cause the cancer? In a typical toxic tort case, the burden would be on the firefighter. But in Colorado there is a special statute that shifts the burden to the employer to prove that the employment could not have caused cancer, and that it did not cause cancer in this firefighter. The court found the employers’ evidence did not meet that burden because it could not disprove the presumption that employment-related exposure to toxic substances was the source of the cancer.