A hybrid carcinoma: adenoid cystic carcinoma and salivary duct carcinoma of the salivary gland. An immunohistochemical study.

Hybrid tumours of the salivary glands are very rare entities composed of two different tumours, each of which conforms with an exactly defined category. We describe an unusual hybrid carcinoma of the palate; it was comprised of an adenoid cystic carcinoma and a salivary duct carcinoma with a transitional region. These two different compartments showed different characteristics as regards cellular differentiation, proliferative activity, and expression of oncogene and tumour suppressor oncogene proteins, as revealed by using markers for muscle actin, keratin, vimentin, S-100 protein, GFAP, Ki-67, p53, and c-erbB-2 proteins. This case is the first reported with overexpression of p53 and c-erbB-2 proteins in the tumour entities. Salivary gland tumours consist of heterogeneous histological groups, and each has morphological diversity. This case indicates that some of the oncogene and tumour suppressor oncogene proteins may help to produce the histological heterogeneity of the salivary gland tumour.