In Massachusetts, for work related injuries that occurred on or after 1/1/1986, a workers' compensation claim must be filed with the insurer within four (4) years of the date an employee becomes aware of the causal connection between their disability and their employment. In the case of the death of an employee, the claim must filed be within four (4) years of the date of death. If you recieve a notice of denial from the insurer (or a Form 104), you have four (4) years from the date you received that denial (or Form 104) to appeal the denial.
If you fail to file the claim or appeal a denial in time, you will be forever barred from filing your claim. Don't delay.