To determine if the neoplastic cells in KPIC tumors have the characteristics of ductal lineage, we stained tumor tissue with Sox-9 antibody, which showed that these KPIC tumor cells are positive for Sox-9 staining, as shown in KIC tumor (Fig 1E). Taken together, these findings show that spontaneous tumors in KPIC mice exhibit characteristics typical of aggressive human PC. The gene discussed is SOX9; the disease is pachyonychia congenita.