NR4A1 and metastatic neoplasm: Several markers have been investigated to this end (such as hormone receptors, p63, p40, several keratin polypeptides), but it seems that none is absolutely specific so as to reliably distinguish metastatic tumors from primary ones [28,29], especially in the case of adenocarcinomas, which can be metastatic (namely from the breast) or originate from the sweat gland apparatus of the skin.