Low-grade malignant myoepithelioma arising in a pleomorphic adenoma: a rare case

Abstract

Malignant myoepithelioma is a very rare salivary gland tumor that can arise de novo or within a pre-existing pleomorphic adenoma. We report a case of malignant myoepithelioma most probably arising in a pre-existing pleomorphic adenoma of the left parotid gland. The patient was a 60-year-old man who presented with a multinodular mass lesion over left side of the face and neck. He had undergone removal of a pleomorphic adenoma of the left parotid gland twice (8 and 22 years ago). Histological examination showed locally concentrated highly invasive myoepithelial cells with bland-looking morphology and no evidence of mitosis or necrosis. Immunohistochemistry confirmed the myoepithelial differentiation (S- 100+, SMA+) and a low Ki-67 labeling index (<5%).

Figure 1

Pelomorphic adenoma of the parotid gland. A well-defined tumor has a thin fibrous capsule and shows chondroid stroma resembling the hyaline cartilage (hematoxylin and eosin stain, 100×).

Figure 2

Left parotid area swelling, showing the multinodular mass with focally ulcerated skin.

Figure 3a

Sheets and thick cords of ovoid to spindle cell component with moderate amount of pale to eosinophilic cytoplasm (hematoxylin and eosin stain, 100×).

Figure 3b

Uniform, mildly hyperchromatic nuclei and inconspicuous nucleolei (hematoxylin and eosin stain, 400×).

Figure 4

Maxillary bone permeation by the tumor (hematoxylin and eosin stain, 400×).