Necrotizing squamous/mucinous metaplasia in oncocytic salivary gland tumors. A potential diagnostic problem

Tumor necrosis and squamous and/or mucinous metaplasia was found in 4 of 26 oncocytic salivary gland tumors (24 Warthin's tumors and 2 oncocytomas). The necrosis was extensive in two cases, producing architectural and cytologic atypia sufficient to simulate a squamous carcinoma. In a third tumor, necrotic and inflammatory debris occurred within dilated tumor spaces exhibiting squamous and mucinous foci, suggesting low-grade mucoepidermoid carcinoma. Adequate sampling revealed Warthin's tumors in all four cases. An additional 13 tumors showed incidental foci of squamous metaplasia, often accompanied by stromal scarring but without necrosis. Four of these tumors also had focal mucinous metaplasia. In the adjacent non-neoplastic salivary gland, oncocytic metaplasia of ducts was seen in 22 glands; there were 7 oncocytic cysts and 3 oncocytic nodules. The tumor necrosis and metaplasia are reminiscent of necrotizing sialometaplasia of the minor salivary gland, thought to be ischemic in origin. The etiology of necrotizing squamous/mucinous metaplasia described here and the extent to which oncocytosis contributes to these changes is unknown. Possibly the extravasation of oncocytic and/or mucinous secretions or cyst contents may result in the reactive changes observed. Necrotizing sialometaplasia and squamous/mucinous metaplasia of oncocytic tumors appear to be related only morphologically, but the shared histologic features may be useful in excluding the diagnosis of salivary gland carcinoma.