A.) Control shRNA and PTEN shRNA BON cells were injected into the pancreas of athymic nude mice (n = 10). Following sacrifice, serum was obtained from each mouse, and serotonin concentration was assessed. Serotonin concentration in the serum relative to total body weight was significantly less in the mice with tumors derived from BON shPTEN cells (*, p = 0.012). B.) The urine concentration of the serotonin metabolite 5-HIAA relative to total body weight was decreased in mice with BON shPTEN-derived tumors (*, p = 0.0059). C.) Immunohistochemical analysis of representative tumor sections demonstrated similar staining of TPH1 in primary tumors derived from BON shPTEN and BON shControl cells and decreased expression of TPH1 in liver metastases compared to primary tumors (100x). D.) Parental BON cells were injected into the spleen of athymic nude mice, and TPH1 expression was less in the metastatic tumors compared to the corresponding primary tumors (200x).