Tyler Mane, Known For Michael Myers 'Halloween' Role, Has Breast Cancer

Tyler Mane -- famous for playing Michael Myers in the "Halloween" films and Sabretooth in the "X-Men" franchise -- is gearing up for the fight of his life ... revealing he's been diagnosed with an extremely rare form of breast cancer.

The actor shared the shocking diagnosis over social media, telling fans he was starting chemotherapy.

Tyler says on 1% of breast cancers are found in men ... and it's often not caught until the later stages.

That's exactly why Tyler says he's going public with his diagnosis ... hoping to raise awareness while inviting fans to join him on his journey to "kick this thing in the ass."

The video ended on a defiant note, cutting to footage of Tyler sitting in a hospital chair hooked up to an IV before flipping off the camera and delivering a blunt message: "F*** cancer."

Tyler is best known for portraying the iconic slasher Michael Myers in 2007's "Halloween" and 2009's "Halloween II."