Ryan O'Neal and Warren Buffet have prostate cancer: What are stages 1 and 2? Left: Actor Ryan O'Neal arrives at the Smithsonian Institution's National Museum of American History Feb. 2, 2011 in Washington, D.C. / Right: Warren Buffett attends a 2008 State Farm Basketball Challenge exhibition game at the Thomas & Mack Center July 25, 2008 in Las Vegas, Nevada. (CBS News) Actor Ryan O'Neal recently revealed that he had been diagnosed with state 2 prostate cancer. While he claims that doctors are positive about his recovery because his disease was caught early, he admitted in a statement he was "shocked and stunned by the news," according to CBS News. O'Neal's announcement was followed on Monday by famed investor and business magnate Warren Buffet's disclosure that he was suffering from stage 1 prostate cancer, CBS News Moneywatch reported. In a letter to investors, Buffett said he received his diagnosis last Wednesday after undergoing a PSA test and biopsy, and will undergo a two-month treatment of daily radiation starting mid-July. I will let shareholders know immediately should my health situation change. Eventually, of course, it will; but I believe that day is a long way off," he wrote. Ultrasound prostate cancer treatment may reduce side effects, study shows PICTURES: Prostate cancer self defense: Nine deadly myths The announcements by these two men put the spotlight on a cancer that strikes nearly 242,000 men each year. But, what is the difference between stages 1 and 2? Cancer is divided into four different stages with the higher the number, the more advanced the disease is. According to the National Cancer Institute, stage 1 indicates the cancer is found in one-half or less than one-half of one lobe of the prostate and stage 2 prostate cancer indicates that the cancer has not spread outside the prostate. Stage 2 prostate cancer is divided into stage 2A and 2B depending how much of the lobe or both lobes of the prostate are affected. The cancer stage is determined by PSA levels, a protein made by the prostate gland and found in the blood, and Gleason scores, a ranking determined by microscopic appearance of the cancer. Screening for prostate cancer is especially important because it can be hard to diagnose at earlier stages because patients have little or no symptoms. Stage 1 prostate cancers cannot be felt during digital rectal exams and are not visible during imaging, and can only be determined by biopsy. Still, according to the National Institute of Health, it is the most common cause of cancer death in men over 75. High risk individuals include African-American men, men over 60, men with a father or brother who had the disease, men who drink too much alcohol, farmers, plant workers and those who have exposed to Agent Orange. There will be about 241,740 new cases of prostate cancer and about 28,170 men will die of prostate cancer this year alone, according to the American Cancer Society. If abnormal results are shown through PSA test and an exam, the cancer will probably be at an earlier stage and therefore more treatable than if someone waited for severe symptoms. However, while early results from a U.S. study have shown that annual screening with PSA and DRE found more prostate cancers than in men who skipped screening, it did not lower the death rate at all, the American Cancer Society noted. A European study did show a lower risk of death with more screening, but noted that 1,400 men would have to be screened and 48 treated before one death would be prevented. Neither study showed that evidence of early high PSA levels helped save lives. Early-stage prostate cancer is mainly treated by two ways: radical prostatectomy and radiation therapy. Radical prostatectomy involves surgical removal of the tumor-affected organ, while radiation therapy uses x-rays to kill cancer cells. Both can be very damaging to the surrounding tissue, leading to many side effects including the inability to maintain an erection for intercourse, urinary incontinence and rectal problems. There are some promising new experimental therapies, including a high-intensity focused ultrasound (HIFU) that research has shown does not cause many of the feared effects, HealthPop reported. Because there are such negative consequences with treatments, some doctors recommend "watchful waiting" for people with early-stage prostate cancer. This halts any therapy until any symptoms appear. Many suggested treatments depend on age and expected life span, other health conditions and the chances that the treatment will cure the patient's prostate cancer. Typically, "watchful waiting" is recommended for those with slow growing cancers that will probably remain in the prostate and those who get the disease when they are much older. Those with stage 1 cancers typically employ watchful waiting and radiation therapy only, and may consider surgery to remove the prostate if young and healthy. If the cancer has spread to other organs, as it does in later stage prostate cancers, patients may need hormone therapy, more extensive surgery and chemotherapy. For more on prostate cancer, visit the National Institute of Health's website.