Blood samples will be collected from patients with melanoma (200), prostate cancer (200), other solid tumor cancers (up to 400), benign hematologic conditions (100), and healthy volunteers (up to 100). Sequential samples will be obtained from selected patients during disease progression or treatment response to allow exploration of potential correlation of CTC with response to treatment, progression-free survival and overall survival. Samples will be immediately de-identified and assigned a numerical code, dated and sent to TrueCells, LLC. Once donated, sample ownership passes to TrueCells, LLC.