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Roughly one in six men will be diagnosed with prostate cancer at some point in their lives, but these cancers usually aren't life-threatening. The least risky form of the disease occurs frequently with age, will not metastasize to other parts of the body, and it doesn't require any immediate treatment. So, should it even be called cancer?

Researchers are developing tools for predicting how fast prostate cancer might progress; among the most promising are those that count circulating tumor cells (CTCs) in blood samples. Research shows that high CTC counts predict poorer survival and faster disease progression. But they are also predictive for early-stage metastatic prostate cancer that still responds to hormonal therapy.