Pleomorphic Adenoma of the Palate with Bizarre Ductal and Myoepithelial Cells: A Case Image.

Abstract

Background: Pleomorphic adenomas (PAs), the most common salivary gland tumors, are comprised of ductal epithelial and myoepithelial cells within a stromal background. A rare subset of PAs exhibits bizarre cells and 12q amplification involving HMGA2 and MDM2; in reported cases, bizarre cells have been confined to the myoepithelial component. We report the first case of a PA with bizarre-cytological features in both the ductal and myoepithelial components.

Case presentation: A 75-year-old woman presented with a palatal mass. Histology revealed a well-circumscribed biphasic tumor with marked nuclear pleomorphism in both luminal ductal and non-luminal myoepithelial cells. Despite the alarming atypia, mitotic activity was low, and neither necrosis nor invasive growth was observed. Immunohistochemically, luminal bizarre cells exhibited ductal characteristics, whereas non-luminal bizarre cells exhibited myoepithelial characteristics. Tumor cells were negative for androgen receptor and HER2 and showed a p53 wild-type expression pattern. The Ki-67 labeling index was < 5%, and the bizarre cells rarely tested positive. Molecular analysis demonstrated amplification of HMGA2 and MDM2, whereas no other pathogenic variants related to salivary gland tumors were detected. Complete excision was performed; no evidence of recurrence or metastasis was observed after 10 months.

Conclusion: Marked cytological atypia of bizarre cells in PA, even when involving ductal cells, may not necessarily indicate malignancy. This case highlights the value of integrating clinicopathological and genetic findings to better define PAs with bizarre cells and prevent overdiagnosis of carcinoma based on atypia alone.