Mist1: a novel nuclear marker for acinic cell carcinoma of the salivary gland

Muscle, intestine, and stomach expression 1 (Mist1) is a transcription factor that functions in the development of granule organisation in serous exocrine cells of the gastrointestinal tract. The aim of this study was to investigate whether Mist1 can be used as a marker for acinic cell carcinoma (AciCC) of the salivary gland. Immunohistochemistry (IHC) was used to analyse Mist1 expression in AciCC (n = 26), secretory carcinoma (SC; n = 18) and 12 other types of salivary gland tumours (n = 99). Strong Mist1 staining was observed in normal serous acinar cells and plasma cells. Mist1 was diffusely expressed in AciCC, with the immunostaining intensity ranging from moderate (4/26) to strong (22/26). Most SC specimens were either negative (7/18) or focally and mildly positive (9/18) for Mist1. Only two SC cases demonstrated a moderate level of Mist1 staining. When moderate-to-strong Mist1 staining was used as the criterion of positivity, all the tested salivary gland tumours other than AciCC were negative for Mist1, except for two cases of SC. Previously cut tissue sections and decalcified specimens exhibited reduced Mist1 immunostaining intensity, which may give false-negative results. In summary, Mist1 is a sensitive marker for serous acinar cells of salivary glands and AciCC, and background non-tumour acinar cells and plasma cells can serve as good internal positive controls.