Hollywood actor Ben Stiller reveals he had prostate cancer but is now cancer-free .

The star of Zoolander was diagnosed with a tumour in 2014.
He says he now wants to share his story to lend his support for a controversial test which saved his life.

The actor says the test is criticised because it can lead to unnecessary "over-treatment" but says men should at least be given the option so they stand a chance of early detection.