WELL-DIFFERENTIATED ENDOCRINE TUMORS OF THE MIDDLE-EAR AND OF THE HINDGUT HAVE IMMUNOCYTOCHEMICAL AND ULTRASTRUCTURAL FEATURES IN COMMON

The immunocytochemical analysis of two cases of well-differentiated en docrine tumours (carcinoids) of the middle ear revealed predominant ce ll populations producing pancreatic polypeptide (PP)-related peptides, glucagon-related peptides, and serotonin (the latter only in one case ). In consecutive sections PP- and glucagon-related immunoreactivities mainly colocalized in the same tumour cells. Ultrastructurally tumour cells were characterized by medium-sized to large granules of moderat e to high density, on which PP and glicentin were localized by the imm unogold technique. No amphicrine cells were found. These features are consistent with those of similar tumours in the rectal mucosa that are mainly composed of L cells coexpressing both PP-related and glucagon- related peptides. Additional tumour antigens of hindgut type detected immunohistochemically were prostatic acid phosphatase and CAR-5 mucin. Expression of the CAR-5 antigen was also found in samples of normal m iddle ear mucosa, in which endocrine cells have not been identified. I n case 1 peritumoral mucosal invaginations showed a proliferation of e ndocrine cells identical immunophenotypically to tumour cells, possibl y representing a precursor lesion. It is concluded that well-different iated endocrine tumours of the middle ear are a distinct pathological entity characterized by multiple hormone production, typically involvi ng three classes of hormones (pancreatic polypeptide-related peptides, glucagon-related peptides, and serotonin) of the hindgut endocrine sy stem.