It has been suggested that prostate cancers arise from the terminally differentiated luminal cells 58,59 because the bulk population of tumour cells, in the most common form of prostate cancer, express luminal cell-specific markers (cytokeratins 8, 18 AR, PSA and PAP), but lack expression of basal cell markers, such as p63. The gene discussed is KLK3; the disease is prostate cancer.