The existence of atypical melanocytes on the mucosa surrounding the tumour supports the ectopic melanocyte theory.[sup.2] According to this theory, precursor melanocytes arise in the neural crest and migrate to the bladder.[sup.2,3,8] Another theory is that argyrophil
urothelial cells are derived from urothelial stem cells with differentiation in the direction of neoplastic melanocytes.[sup.2,6,9] In our case, pigmented melanocytes around the tumour supported the primary origin.