A case of midgut carcinoid with breast metastasis and cellular localization of serotonin and substance P

A case of midgut carcinoid with breast metastasis is reported. Hepatic metastases stored large amounts of serotonin as demonstrated by the Falck-Hillarp technique. Immunocytochemically serotonin and substance P, which may co-exist in gut enterochromaffin cells, were demonstrated in separate populations of tumor cells both in the hepatic and mammary neoplasms.