RGCC and prostate cancer: In the absence of good HES6 antibodies that are reliable for immunohistochemistry (Hartman et al, 2009), we checked protein expression of the HES6-associated cell cycle regulator polo-like kinase 1 (PLK1) in representative samples of benign, primary prostate cancer and CRPC tissue (Fig 4E), identifying strong expression in CRPC tissue only.