<qa>  What is the most common solid tumor?Prostate cancer is the most common solid tumor and the second leading cause of cancer death among American men. While surgery, radiation and observation have all been deemed appropriate for newly diagnosed men, tremendous uncertainty remains regarding the optimal treatment. AHRQs 2008 evidence report on the comparative effectiveness of therapies for localized prostate cancer concluded that no one therapy can be considered the preferred treatment for localized prostate cancer due to the limitations in the body of evidence as well as the likely tradeoffs an individual patient must make between estimated treatment effectiveness, necessity and adverse effects. The existing literature is limited by its focus on older therapeutic modalities and failure to control for individual patient characteristics and providerhospital characteristics that may influence outcomes quality of care. To fill these evidence gaps, we propose to expand a network of state tumor registries and a national observational disease registry to establish a new population-based cohort of men newly diagnosed with localized prostate cancer. We will prospectively measure key patient-reported outcomes, such as health-related quality of life and side-effects of therapy at diagnosis and 6 and 12 months later. We will also collect detailed medical record information, including clinical data, technical details of the interventions, complications, short-term cancer recurrence rates, and quality-of-care indicators. 