"At first, I didn't know what was going to happen. I was scared," he told Stern. "The one thing that it does is it just stops everything in your life when you get diagnosed with cancer because you can't plan for a movie — you don't know what's going to happen."

Now, Stiller is opening up about his cancer battle to help others. Though the PSA test is controversial, he believes it can save lives. As he wrote on Medium, "In this imperfect world, I believe the best way to determine a course of action for the most treatable, yet deadly cancer, is to detect it early."

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