The PSA test provides some important object lessons. It can detect a broad spectrum of prostate cancers. However, prostate cancers are a heterogeneous group—ranging from rapidly progressing and aggressive to slowly progressive or nonprogressive. Treating the last group may lead to the erroneous conclusion that these patients were “cured” by screening and treatment. If unscreened and untreated, these same men might simply have gone on to die from other causes—at the same point in time. Early diagnosis based on screening may also lead to the erroneous assumption that screening increases true survival time, since survival is measured from the time of diagnosis—longer in the case of the screening diagnosis compared with the time when the patient becomes symptomatic (the “lead time” bias).