A case of secretory carcinoma of the parotid gland provides cytological clues for the differential diagnosis of this disease

Abstract

| INTRODUCTIONCytopathological diagnosis of salivary gland neoplasms can be difficult because of their infrequency and the diverse cytomorphology of the various histological types. Consequently, cytopathologists often have limited experience with these tumours. Secretory carcinoma (mammary analogue secretory carcinoma) is a newly recognised tumour of the salivary gland, first described by Sk alov a et al in 2010. 1 The histological, immunohistochemical and molecular characteristics of this tumour resemble those of secretory carcinoma of the breast. Secretory carcinoma was previously categorised as an acinic cell carcinoma with papillary-cystic, microcystic or follicular growth patterns; however, secretory carcinomas have an ETV6-NTRK3 gene fusion resulting from the t(12;15)(p13;q25) chromosomal translocation. 1 Here, we describe cytological findings from a case of secretory carcinoma and discuss cytological diagnostic clues for differential diagnosis between secretory carcinoma and other malignant tumours of the parotid gland. | CASE HISTORYA 35-year-old Japanese woman presented with a right infraauricular swelling. Magnetic resonance imaging examination detected a tumour in the superficial lobe of her right parotid gland. Cytological diagnosis from FNA was indeterminate, but the tumour could not be excluded as low-grade malignancy.The patient underwent a tumourectomy with superficial parotidectomy. | MATERIALS AND METHODSCytological specimens obtained from FNA were subjected to Papanicolaou staining and periodic acid-Schiff (PAS) reaction. Formalin fixed and paraffin embedded histological specimens were stained with haematoxylin and eosin, and PAS with and without diastase digestion. An immunohistochemical panel that included mammaglobin, vimentin, cytokeratin 19, S-100 protein, GCDFP-15, MUC1, DOG-1, HER2, p63, androgen receptor and MIB-1 was examined. Reverse transcription-polymerase chain reaction analysis of ETV6-NTRK3 mRNA expression from tissue samples was also performed. | RESULTS | Cytological findingsPreoperative Papanicolaou staining revealed numerous cohesive cell clusters and discohesive tumour cells. Cell clusters showed a papillary architecture with capillaries or an irregularly shaped and somewhat loose connective structure. In each papillary cluster, tumour cells were attached to capillaries in layers varying from one to several cells thick ( Figure 1A, B). Irregularly shaped clusters exhibited either smooth or fuzzy margins. Tumour cells were polygonal or cuboidal, and of uniform size. Nuclei were round-to-oval in shape, and were bland with pale and fine granular chromatin. The cytoplasm was acidophilic or vacuolated. The nuclear-to-cytoplasmic ratio was low-to-moderate. Cytoplasmic vacuoles varied in number and size; however, single large vacuoles were conspicuous ( Figure 1C, D). The ratio of tumour cell types within each cell cluster varied