Currently, the 'Workers' Compensation Act of Colorado' provides that certain cancers contracted by firefighters are considered occupational diseases presumed to have been a result of the firefighters' employment. A firefighter's employer or an insurer may rebut this presumption by showing by a preponderance of the medical evidence that the cancer did not occur on the job.     The act expands the types of cancer that are considered occupational diseases and strengthens the rebuttable presumption to require an employer to show clear and convincing evidence that the cancer did not occur on the job.     The act exempts firefighters who are employed by the state.(Note: This summary applies to this bill as enacted.)