title: Hybrid tumours of salivary glands. Definition and classification of five rare cases.
abstract: Hybrid tumours are very rare tumour entities which are composed of two different tumour entities, each of which conforms with an exactly defined tumour category. The tumour entities of a hybrid tumour are not separated but have an identical origin within the same topographical area. In contrast, biphasically differentiated tumours are a mixture of two cellular patterns with a corresponding term in the tumour classification. Examples of a biphasic differentiation are: basaloid-squamous carcinoma, adeno-squamous carcinoma or sarcomatoid carcinoma, and epithelial-myoepithelial carcinoma, mucoepidermoid carcinoma or adenoid cystic carcinoma. Hybrid tumours must also be distinguished from the multiple occurrence of salivary gland tumours which can develop syn- or metachronously. In the tissue samples of more than 6600 salivary gland tumours covered by the Salivary Gland Register (Institute of Pathology, University of Hamburg, Germany) only 5 cases of hybrid tumours were recorded between 1965 and 1994. This means less than 0.1% of all registered tumours. Case 1 was a very rare example of a hybrid adenoma with differentiation as a basal cell adenoma and a canalicular adenoma of the parotid gland. The similar cellular origin of both types of adenoma may be an explanation for its development in a hybrid adenoma. Case 2 is a hybrid tumour with a composition of basal cell adenoma and a glandular type of adenoid cystic carcinoma. In both types of tumours the two cell types (duct-lining cells and modified myoepithelial cells) have a similar histogenetic origin. Therefore, the development of the both cell types in a hybrid tumour with two trends of differentiation is possible. Case 3 represents a hybrid adenoma as a mixture of a Warthin tumour and a sebaceous adenoma. Although inclusions of sebaceous cells are observed in Warthin tumours, this hybrid tumour shows a composition of two different epithelial structures in a varied mixture. Case 4 is a very rare and unique hybrid carcinoma with two absolutely different components: acinic cell carcinoma and salivary duct carcinoma. The poor prognosis of this hybrid carcinoma is determined by the salivary duct carcinoma. Case 5 represents a hybrid carcinoma whose two components have a similar histogenetical basis: epithelial-myoepithelial carcinoma and a glandular type of adenoid cystic carcinoma. Both carcinomas are composed of variable proportions of ductlining cells and myoepithelial cells.
authors.affiliation: Institute of Pathology, University of Hamburg, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Seifert
authors.forename: K
authors.initials: K
authors.lastname: Donath
mesh_terms: D000368:Aged; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009378:Neoplasms, Multiple Primary / Q000145:classification / Q000473:pathology*; D016609:Neoplasms, Second Primary / Q000473:pathology; D010307:Parotid Neoplasms / Q000473:pathology; D012468:Salivary Gland Neoplasms / Q000145:classification / Q000473:pathology*