Practical pathological methods for reliable diagnosis of secretory carcinomas of the salivary gland.

Secretory carcinomas (SCs) of the salivary gland have recently been recognized as low-grade, malignant tumors. Before this designation, most SCs were diagnosed as variants of acinic cell carcinomas (AciCCs). SCs harbor the t(12;15)(p13;q25) translocation that generates an oncogenic fusion gene, ETS variant transcription factor 6/Neurotrophic tyrosine receptor kinase(ETV6::NTRK3). However, detecting fusion genes in a clinical setting is time-consuming and costly. In this study, we examined 31 cases previously diagnosed as AciCC and SC using pathological analyses with detection of fusion genes using ETV6 break-apart fluorescence in-situ hybridization and reverse transcription-polymerase chain reaction. After re-analysis, we found that these 31 cases actually comprised 21 SCs and 10 AciCCs. We examined the diagnostic utility of immunohistochemistry by comparing results with the fusion gene, Pan-Trk, which despite having recently been reported as effective for diagnosis of SC, was not universally accurate. However, combining mammaglobin and S-100 could be particularly useful in diagnosing SC. This practical method will contribute to accurate diagnosis of SCs, while saving time in daily clinical practice.