Myoepithelial cell-rich neoplasms: cytologic features of benign and malignant lesions

Lesions that contain abundant myoepithelial cells may present as a diagnostic challenge in fine-needle aspiration (FNA) specimens. Potential diagnostic problems may arise due to morphologic heterogeneity of myoepithelial cell-rich lesions and difficulty in predicting malignancy in FNA specimens. An accurate diagnosis is important, because malignant myoepithelial cell-rich lesions require a wider local excision and lymph node dissection. The authors characterized the cytologic features of myoepithelial cell-rich lesions in an attempt to define the criteria that facilitate distinction between benign and malignant tumors.

FNA biopsies of myoepithelial cell-rich lesions with corresponding histologic specimens were selected. The cytology specimens were evaluated for the following criteria: cellularity, cell morphology, pleomorphism, chromatin pattern, presence of nucleoli, background material, necrotic debris, and presence of mitotic figures. A review of the histologic sections was performed for diagnostic confirmation.

Seventeen specimens from 17 different patients were selected. The histologic diagnoses were myoepithelial carcinoma (n = 6 patients), malignant mixed tumor with predominant myoepithelial carcinoma (n = 2 patients), epithelial-myoepithelial carcinoma (n = 1 patient), and benign mixed tumor (n = 8 patients). The primary sites included the parotid gland (n = 10 patients), submandibular gland (n = 3 patients), minor salivary gland (n = 3 patients), and breast (n = 1 patient). Most specimens, whether they were benign or malignant, were very cellular. Pleomorphism, coarse chromatin, prominent nucleoli, mitotic figures, and necrosis were observed only in malignant specimens. Background material and ductal cells were seen in both benign and malignant specimens.

The presence of pleomorphism, coarse chromatin, prominent nucleoli, mitotic figures, and/or necrosis should raise the possibility of myoepithelial carcinoma in FNA specimens from myoepithelial cell-rich lesions.