Olivia Munn reveals breast cancer diagnosis

Actress Olivia Munn revealed that she had undergone a double mastectomy after being diagnosed with breast cancer.

The X-Men: Apocalypse and The Newsroom performer took to Instagram to tell followers the news, just days after she attended the Oscars ceremony with her partner, comedian John Mulaney.

The 43-year-old said the cancer had been discovered almost a year ago after her doctor noted she was at elevated risk for the disease and suggested she undergo an additional scan, 12 months before a routine screening.

"I wouldn't have found my cancer for another year—at my next scheduled mammogram," she told followers.

After initial tests, a biopsy was ordered.

"The biopsy showed I had Luminal B cancer in both breasts. Luminal B is an aggressive, fast moving cancer," she wrote, adding that the double mastectomy was performed 30 days later.

"I went from feeling completely fine one day, to waking up in a hospital bed after a 10-hour surgery the next," she wrote in a post, with photos taken apparently during her treatment.

"I'm lucky. We caught it with enough time that I had options. I want the same for any woman who might have to face this one day."

Munn walked the red carpet at Sunday's Academy Awards ceremony in Hollywood, where Mulaney presented an Oscar, and later attended the celebrity-filled Vanity Fair after party.

Munn's small screen credits include The Daily Show with Jon Stewart as well as a role in Aaron Sorkin's HBO drama The Newsroom.

Her movie credits have included Magic Mike, The Predator, and Office Christmas Party. (AFP)