Coexpression of cytokeratin, neurofilament and vimentin in carcinoid tumors.

The immunohistochemical expression of intermediate filaments was investigated in 56 carcinoid tumors from 50 cases including 31 rectal and 25 non-rectal sites. Cytokeratin was the most frequently expressed in 55 of the tumours. Only one tumour of the stomach was negative for cytokeratin. Neurofilament (68 kd and 160 kd) was positive in 25 (44.6%) tumours with no preferential pattern of expression in particular tumours. Vimentin was positive in 18 out of the 31 rectal carcinoids (58%), and 3 of the 25 non-rectal carcinoids (12%). There was a significant difference in vimentin immunoreactivity between rectal and non-rectal carcinoids. The coexpression of cytokeratin and neurofilament was 44.6% and that of cytokeratin and vimentin was 37.5%. The coexpression of all three types of intermediate filament was 35.5% in rectal carcinoids, but 8% in non-rectal carcinoids. The present study revealed coexpression of cytokeratin, neurofilament and vimentin in carcinoids and an especially high incidence of vimentin expression in those of rectal origin.