Answer: In-situ malignant ex-mixed tumor

Histology: The submandibular gland harbors a well-circumscribed and encapsulated nodule. In some areas of the tumor, strands of epithelial cells are embedded in a richly myxoid stroma. At higher power, these cells have a very bland cytological appearance. In other areas of the tumor, the stroma is very scant and has been replaced by a densely cellular proliferation of epithelial cells. At higher power, these cells exhibit nuclear enlargement, moderate pleomorphism, and prominent nucleoli. Mitotic figures are readily identified in these cellular areas.

Discussion: Carcinoma ex-mixed tumor refers to a benign mixed tumor that has undergone carcinomatous transformation. The carcinomatous component is recognized by overtly malignant cytologic atypia and by invasive tumor growth beyond the tumor capsule. A benign mixed tumor that harbors areas of significant cytologic atypia within the confines of its capsule is referred to as in-situ malignant ex-mixed tumor. Other terms include “intracapsular” carcinoma and “non-invasive” carcinoma ex-mixed tumor.

Despite its worrisome cytological features, the prognosis of an in-situ carcinoma is excellent provided that the carcinoma is indeed confined and the tumor has been completely excised. Accordingly, the interface of the tumor and the surrounding tissues should be extensively sampled for histopathologic evaluation. Indeed, all of this region should be sampled in an effort to exclude the possibility of focal microscopic tumor invasion.