Fine-needle aspiration cytology of myoepithelial carcinoma of salivary gland: Diagnostic challenge to cytopathologist
A 37-year-old female patient presented with painless, progressive swelling in the infra-auricular area since 2 years. Examination with palpation revealed a smooth surfaced, mobile swelling measuring approximately 3 cm × 2.5 cm. There was no evidence of facial nerve involvement. FNA cytology was performed with 23G needle. The aspirate was stained with May-Grünwald-Giemsa stain. On examining cytological smears, possibilities of cellular pleomorphic adenoma and myoepithelial cell neoplasm were rendered and the patient was advised complete excision. A left superficial parotidectomy with preservation of facial nerve was performed and tumor sent for histopathological examination. Final diagnosis of MC was made on H and E stained section and on immunohistochemistry (IHC). No local recurrence or distant metastasis was found 6 months after surgery.\nCytological smears were highly cellular with the neoplastic cells arranged singly, small groups and as large cohesive fragments []. The large fragments appeared 3D with the high cellularity and nuclear overlapping []. At places, these large fragments showed pseudopapillary appearance with well-defined borders. The tumor cells had epithelioid appearance with a moderate amount of dense, non-granular cytoplasm []. Metachromatic stromal fragments were seen intermixed with neoplastic cells. The nuclei were round to oval, at places eccentrically located with mild nuclear pleomorphism. Background showed numerous naked nuclei and stromal fragments. Two cytological possibilities were forwarded — one of cellular pleomorphic adenoma and second of myoepithelial cell neoplasm. Patient was advised complete excision and histopathological examination for final diagnosis and subtyping.\nSubsequently, we received grey yellow soft-tissue mass measuring 3 cm × 2.5 cm × 2 cm. Cut surface was solid, grey brown with grey white nodules. H and E sections showed a tumor with multinodular growth pattern [] and infiltrative borders. The tumor nodules were composed of epithelioid cells arranged in diffuse sheets, nests and cords. Tumor cells had round to oval nuclei, vesicular chromatin, prominent nucleoli and a moderate amount of eosinophilic cytoplasm [ inset]. Mitotic rate ranged from 5 to 15/10 HPF. No area of necrosis was identified. A panel of IHC comprising of cytokeratin (CK), S-100, smooth muscle antibody (SMA), epithelial membrane antigen (EMA) and glial fibrillary acidic protein (GFAP) was applied. Tumor cells were positive for S-100, SMA and negative for CK, EMA and GFAP. Based on the histopathology and IHC findings, final diagnosis of MC was rendered and patient was kept on follow-up.