Ryan O'Neal's cancer is ''under control.''

The 70-year-old actor was shocked to learn he has stage four prostate cancer recently, but is remaining positive about his chances of recovery.

In an interview with US TV show 'Nightline', he said when he heard he has developed the disease, he thought: ''Why me?' I just sort of chalked it up to bad luck.''

He also told the show he has skin cancer, in the form of a melanoma on his nose, adding: ''Welcome to Malibu and the sun.''

Ryan added he is spurred on in his fight by thinking of his long term partner, Farrah Fawcett, who lost her battle with cancer in 2009.

He added: ''Farrah taught me that - about fighting it. Fight a good fight.''

Ryan - who has four grown up children, Tatum, Griffin, Patrick and Redmond, by three different mothers - says because his cancer has been diagnosed in its early stages, he is hoping to make a full recovery.

He said in a statement: ''Although I was shocked and stunned by the news, I feel fortunate it was detected early and according to my extraordinary team of doctors the prognosis is positive for a full recovery.

''I am deeply grateful for the support of my friends and family during this time, and I urge everyone to get regular check-ups, as early detection is the best defence against this horrible disease that has afflicted so many.''

Ryan has also been treated for leukaemia in the late 90s.

He is planning to release a memoir about his life with Farrah entitled 'Both of Us', due for release in early May.