A Novel Algorithmic Diagnostic Approach to Secretory Carcinoma of Salivary Gland

Background: Secretory carcinoma (SC) is a recently recognized tumour of salivary gland with characteristic t (12; 15) (q13; q25) translocation with ETV6-NTRK3 fusion. SC were misdiagnosed as Acinic cell carcinoma (AciCC), especially Papillary cystic variant (PCV) in the past. Primary objective of the study was to devise diagnostic algorithm to distinguish SC from other low grade salivary gland tumors especially AciCC. Methods: Surgical pathology archives was searched for cases diagnosed as PCV-AciCC from 2005 to 2017 and as SC from 2012-2017. The H&E, IHC and FISH results were studied. Results: Parotid and oral cavity were involved in 74.3% and 14.2% cases. HE b) solid pattern showing multivacuolated bubbly cytoplasm; c) follicular pattern with dense colloid like secretions. A diagnostic algorithm was devised. Of 35 cases, upfront diagnosis of SC was offered in 22 cases. 13 Cases of PCV-AciCC were reclassified as SC based on morphology and confirmed by IHC (diffuse co-expression of mammaglobin, S100 and lack of DOG1 positivity) and molecular study. 65.7% cases showed ETV6 translocation by FISH. Conclusion: SC is a new entity, which was misdiagnosed as PCV-AciCC in the past. SC can originate in minor salivary gland. Awareness of morphological indicators and high index of suspicion is necessary for diagnosis. IHC markers further facilitate the diagnosis. The translocation study can thus be limited to cases with unusual histology and planning of targeted therapy in future. A novel diagnostic algorithm is suggested for recognition of this new entity.