Noninvasive and minimally invasive carcinoma ex mixed tumor: a clinicopathologic and ploidy study of 12 patients with major salivary tumors of low (or no?) malignant potential.

We studied 12 histologically malignant salivary tumors that showed complete encapsulation or only limited microscopic invasion. Most cases were histologically characterized by atypical and mitotically active luminal cells forming dilated, angular, variably sized glands in the subcapsular region, varying proportions of nonluminal tumor cells, and a background of central fibrosed hyalinized stroma. The appearance is that of a low-grade carcinoma. Focal higher grade carcinoma was superimposed on this histologic data in three cases. Neither recurrences nor metastases were seen in 11 of 12 patients after surgical resection with a follow-up of 1.2 to 13 yrs (mean, 4.2 years). Ploidy studies were performed on the paraffin-embedded tissue in 11 cases and yielded results for 7 cases. Aneuploid cell populations were found in five tumors; two had normal diploid populations; and the ploidy results are not predictive of tumor behavior. This type of salivary gland tumor fits diagnostically within the category of noninvasive and minimally invasive carcinoma ex pleomorphic adenoma (also referred to as in situ and low-grade malignant mixed tumors), a class that requires additional awareness and precise recognition as it signifies a good prognosis after surgical resection.