Cytokeratin expression and epithelial differentiation in Warthin's tumour and its metaplastic (infarcted) variant

Aims: Warthin's tumour is characterized by a bilayered columnar epithelium. Transformation into metaplastic (infarcted) Warthin's tumour includes squa mous metaplasia of the epithelium along with regressive changes in the stro ma. Misinterpretation of metaplastic Warthin's tumour for malignancy is a s erious diagnostic pitfall. This study assesses the utility of cytokeratin e xpression in Warthin's tumour and its metaplastic variant. Methods and results: Twenty-six cases of Warthin's tumour, among them eight metaplastic Warthin's tumours, were investigated employing immunohistochem istry. Both Warthin's tumour and its metaplastic variant regularly expresse d cytokeratins (CK) 7, 8. 18, and 19. Staining results with antibodies to C K10, 10/13, 1/2/10/11, and 20 were negative in all specimens. Immunoreactiv ity for CK 5/14 and 17 was restricted to basal cells in Warthin's tumour, b ut involved basal as well as surface cells in metaplastic Warthin's tumour. Conclusions: Warthin's tumour and its metaplastic (infarcted) variant both express CK 7, 8, 18, and 19, which are typical for columnar differentiation . Cytokeratins typical of squamous differentiation are absent from Warthin' s tumour and its metaplastic variant, irrespective of the squamous morpholo gy of the epithelium in metaplastic Warthin's tumour. The expression of CK 5/14 and 17, which are typical of regenerative cells, is restricted to basa l cells in Warthin's tumour, but is expressed also in surface cells in meta plastic Warthin's tumour.