Usefulness of immunohistochemistry to distinguish between secretory carcinoma and acinic cell carcinoma in the salivary gland

概要

〔目的(Purpose)〕
　Secretory carcinoma (SC) of the salivary gland is a relatively newly described disease, separate from acinic cell carcinoma (ACC), which frequently displays ETV6-NTRK3 gene fusion. However, the differences between SC and ACC remain unclear. Here,we reviewed 12 cases formerly diagnosed with ACC and extracted SC to clarify the pathologic differences between SC and ACC using immunohistochemistry and genetic techniques.

〔方法ならびに成績(Methods/Results)〕
　This study enrolled 12 patients formerly diagnosed with ACC during 2005-2014 at Osaka International Cancer Institute and Osaka University Hospital. Immunohistochemistry of phosphorylated signal transducer and activator of transcription 5 (p-STAT5), SI00 protein, p63, GCDFP15, Mammaglobin,discovered on GIST-1 (DOG1), p53, GATA3, MIB-1 was performed. Cases without obvious acinar-like cells were also analyzed by reverse-transcription (RT) polymerase chain reaction (RT-PCR.) and fluorescence in situ hybridization (FISH) analyses. The primer of RT-PCR was for ETV6-NTRK3 gene fusion detection. In FISH, the Vysis LSI ETV6 Dual Color Break Apart Rearrangement Probe was used.

　Histological reevaluation of 12 formerly diagnosed ACC cases was performed, which yielded a new diagnosis of SC in four cases due to a lack of obvious acinar-like cells. Immunohistochemically, p-STAT5 was expressed in SC but not in ACC, whereas DOG1 was expressed in ACC but not in SC. Molecular analysis was possible in three SC cases, of which two showed the ETV6-NTRK3 fusion transcript on RT-PCR, as well as breaks in the ETV6 gene on FISH. However, the remaining SC cases did not show this fusion transcript.

〔総 括(Conclusion)〕
　Recently, several reports have suggested that SC might not be adequately diagnosed if the focus is placed solely on the ETV6-NTRK3 fusion gene due to genetic diversity. In this regard, immunohistochemistry of p-STAT5 and DOG1 is expected to be a useful alternative diagnostic tool to discriminate SC from ACC.