A significant number of patients with gastroenteropancreatic neuroendocrine tumors (GEP NETs) present with metastatic disease and with unknown primary in about 15% of cases.

We analyzed 163 primaries of GEP NET and 115 metastases for expression of caudal type homebox 2 (CDX2), estrogen receptor (ER), progesterone receptor (PR), somatostatin receptor 2a (SSTR2a) and Ki67.

PR was most often positive in pancreatic NET and only rarely in non-pancreatic NET (p<0.001). ER was more frequently expressed in non-pancreatic NET (p<0.001) and was more often positive in females than males (p=0.019). CDX2 was positive in all primaries of the duodenum, ileum and appendix, but was also detected in 24% of metastases with pancreatic primary. SSTR2a and Ki67 did not differ significantly between primaries and metastases.

Our data substantiate the value of PR, ER and CDX2 in GEP NET, and steroid hormone receptors, being differentially expressed in male and female patients. Differences between primaries and metastases were small but potentially relevant.