Atypical features in salivary gland mixed tumors: their relationship to malignant transformation.

Although criteria for distinction between the benign and malignant elements in carcinoma ex mixed tumor have been adequately described, there have not been any attempts to identify clinical or histologic features in benign mixed tumors that indicate increased risk of malignant change. For this reason, 65 mixed tumors of the major and minor salivary glands that exhibited atypical histologic features were examined in an attempt to analyze which, if any, of these features might indicate a greater likelihood of malignant transformation. The atypical features evaluated were hypercellularity, capsule violation, hyalinization, necrosis, and cellular anaplasia. The mitotic rate was also analyzed. The age of the patient, and the site, size, and prediagnostic duration of the tumor were recorded and, together with the histologic findings, were correlated with follow-up information. Nine (13.8%) of the 65 tumors underwent malignant transformation. Five of these patients died of the tumor, two others had distant metastases and were alive with the disease, and two were free of disease. Benign mixed tumors that showed prominent zones of hyalinization or at least moderate mitotic activity were more likely to develop carcinoma than those that did not. chi 2 analysis indicated that only hyalinization was significant (P < 0.05), but, with Fisher's exact test (two-tailed), this and all of the other features evaluated revealed a P value greater than 0.05. The other atypical features failed to correlate with malignant change. Clinical findings at the initial diagnosis that indicated a greater likelihood of malignant transformation were occurrence in the submandibular gland, older patient age, and large tumor size.