Salivary duct carcinoma cytologically diagnosed distinctly from salivary gland carcinomas with squamous differentiation

It has been difficult cytologically to distinguish salivary duct carcinoma (SDC) from high-grade carcinoma. We investigated the microscopic cytological findings, morphometric image analyses, and immunohistochemical features of SDC, focusing on how we achieved an accurate differential diagnosis distinguishing SDC from salivary gland carcinomas with squamous differentiation. Immunohistochemical staining was performed for androgen receptor (AR), gross cystic disease fluid protein-15 (GCDFP15), mammaglobin, human gastric mucin, MUC1, MUC2, p63, and cytokeratin high molecular weight. Of the 13 cases of SDC, 9 cases showed typical cytological findings of sheet clusters with polygonal granular cytoplasm with fine chromatin. The other 4 cases showed unusual cytological findings of a pseudo-papillary cluster or scattered cells only, and the tumor cells showed coarse chromatin. Morphometric image analysis showed that the nucleus area was statistically different between SDC and salivary gland carcinomas with squamous differentiation. AR-positive expression (P = 0.008), GCDFP15-positive expression (P = 0.005) and p63-negative expression (P = 0.001) were effective as SDC-specific markers in immunohistochemistry. An accurate cytological diagnosis of SDC can be determined by immunostaining with AR, GCDFP15, and p63, based on the nuclear findings.