Malignant mixed tumor of salivary glands is a rare
tumor whose variable behavior and prognosis are related for the most part to the clinical stage and histologic grade of the carcinomatous component. The purpose of this study is to predict prognosis by comparing the histologic grading and subclassification of the carcinomatous component with the immunohistochemical reactivity for
E-cadherin, P53 mutation
protein, and cellular proliferation (Ki67). Stains were performed on
formalin-fixed
paraffin-embedded tissue sections from 18 cases of
malignant mixed tumor. Clinical follow-up was obtained for each patient. Regional lymph node and distant organ
metastases were the criteria for poor prognosis. Of seven cases with lymph nodes
metastasis, five were high-grade
tumors (with one subsequent death from brain
metastasis) and two were low-grade. Of the eight high-grade
tumors, positivity for Ki67, p53, and
E-cadherin were noted in six, four, and two cases, respectively. In contrast, of the 10 low-grade
tumors, two stained with Ki67, five with p53, and none with
E-cadherin. Most notably, all seven metastatic cases (as opposed to only one of 11 nonmetastatic
tumors) had Ki67 reactivity of more than 10%. We conclude that
malignant mixed tumor represents a spectrum of
malignancies in which the clinical behavior is closely related to the carcinomatous
element. In addition to histologic grading, Ki67 is a useful prognostic marker in the evaluation of
malignant mixed tumor while p53 and
E-cadherin appear to be of limited value.