Carcinomatous Transformation of Mixed Tumors of the Parotid Gland

The wide variety of tumors developing in salivary glands has long been recognized, and the controversy over the benignancy or malignancy of certain types is gradually being resolved. For many years the mixed tumor of the parotid and other salivary glands was thought to be malignant, although the degree of malignancy was considered to be low. This concept was partly the result of two factors: (1) the high incidence of recurrence (30% to 40%) after initial surgical treatment and (2) the occasional appearance of an obviously malignant, rapidly growing, and distantly spreading tumor after many years of dormancy. It is generally agreed now, however, that the high recurrence rate of mixed tumors is primarily the result of inadequate surgical removal of the tumor because of fear of injuring the facial nerve. Mixed tumors are not multicentric in origin, as described by McFarland,⁸ but recur or persist because of pseudopods