NYPD cops who worked at Ground Zero after 9/11 had 50 percent more cancer diagnoses than officers did in the years before the terror attacks, a long-awaited study has found.

The NYPD’s 20-year study — the largest ever of cancer among police officers was distributed internally by the department’s chief surgeon Thursday and obtained exclusively by The Post.

Researchers scrutinized the medical records of nearly 40,000 cops who were on the job on 9/11 and tracked their cancer rates through 2014. Post-9/11 retirees’ rates were also tracked. The findings showed 859 cops were diagnosed with cancer, with 11 having more than one case for a total of 870 diagnoses.