Low power H&E stained image of metastasising pleomorphic adenoma
An über rare–circa 60 cases reported in the world literature–salivary gland tumour, which is one of 3 different patterns of malignant change–the other 2 are carcinoma ex pleomorphic adenoma–PA and true malignant mixed tumor (carcinosarcoma)–that occur in PA.
Diagnostic criteria One or more foci of metastatic histologically benign PA, accompanied by a current PA of major or minor salivary gland origin, or a history of previously surgerised PA
Aetiology Uncertain; usually there is a history of a recurrent and/or incompletely excised PA
Metastases Haematogenous or lymphatic spread to bone, head and neck, lungs, and elsewhere–skin, liver, retroperitoneum, kidney, lymph nodes, and CNS