People magazine broke the news last week that veteran actor Ryan O'Neal was diagnosed with prostate cancer. O'Neal, 70, who battled leukemia in the 1990s, told the magazine that his prostate cancer was a stage 4 -- but that his doctor gave him a good prognosis.

Stage 4 cancer means the cancer has metastasized (or spread) elsewhere in the body. Stage 4 is the most difficult stage of cancer to treat, and the survival rate for Stage 4 cancer is usually very poor.

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