The epidemiology of metastases in neuroendocrine tumors.

The epidemiology of metastases in neuroendocrine tumors (NETs) is virtually unknown. The present novel approach took use of two nationwide Swedish registers to assess the distribution of metastatic sites in comparison to adenocarcinoma. 7,334 patients with NET were identified from the Swedish Cancer Registry. Metastatic sites were identified from the National Patient and Cause of Death Registries. Sites of metastasis were investigated depending on the primary site of NET. The metastatic potential of NET was assessed. The liver was the most common site of metastasis (82% of patients with metastases), and the small intestine was the most common source of NET metastases. Of all patients with metastatic lung NETs, 66% had liver metastases, whereas the corresponding number for adenocarcinoma of lung was only 20%. The risk of metastasis was highest if the primary was in the small intestine or pancreatohepatobiliary tract, whereas it was lower with appendiceal and rectal NET. Men had more bone metastases compared to women. Patients with metastatic NET had worse prognosis if the primary site was unknown (11 months, 9% of NET patients) compared to those whose primary was known (19 months). The metastatic potential of NETs varies profoundly depending on the primary site. NETs show a clear preference to metastasize to the liver. Surveillance of liver metastases may enable earlier diagnosis and treatment. In liver metastases from NET, the small intestine should be suspected as the primary site, whereas the lung should be suspected in nervous system metastases of NET origin.