NONINVASIVE AND MINIMALLY INVASIVE-CARCINOMA EX MIXED TUMOR - A CLINICOPATHOLOGICAL 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 com plete encapsulation or only limited microscopic invasion. Most cases w ere histologically characterized by atypical and mitotically active lu minal cells forming dilated, angular, variably sized glands in the sub capsular region, varying proportions of nonluminal tumor cells, and a background of central fibrosed hyalinized stroma. The appearance is th at of a low-grade carcinoma. Focal higher grade carcinoma was superimp osed on this histologic data in three cases. Neither recurrences nor m etastases 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 p erformed on the paraffin-embedded tissue in 11 cases and yielded resul ts for 7 cases. Aneuploid cell populations were found in five tumors; two had normal diploid populations; and the ploidy results are not pre dictive of tumor behavior. This type of salivary gland tumor fits diag nostically within the category of noninvasive and minimally invasive c arcinoma ex pleomorphic adenoma (also referred to as in situ and low-g rade malignant mixed tumors), a class that requires additional awarene ss and precise recognition as it signifies a good prognosis after surg ical resection.