These tumours demonstrate strong, diffuse S100 positivity. Myoepithelial markers (calponin or smooth muscle actin) highlight cells rimming the cystic spaces, confirming the intraductal nature of most, or all, of each tumour. No myoepithelial cells are admixed within the proliferative cellular component. Those tumours studied for HER2-neu antigen are uniformly negative.
Originally, this tumour was reported as a low-grade variant of salivary duct carcinoma. However, as no data have accu mulated definitely relating this entity to ductal carcinoma and since there frequently is a prominent cystic component, for the purposes of this WHO classification, the tumour is listed as a variant of cystadenocarcinoma.
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