Part of this could be due to that the bone metastasis also contains nonepithelial cell types that have no expression of KLK4 transcript, but it is also well known that the expression of KLK3, for example, decreases as the tumor cells become less differentiated [31], and the expression levels are much lower in PC cell lines than in the patient material (data not shown). The gene discussed is KLK4; the disease is pachyonychia congenita.