Low-grade intraductal carcinoma of salivary gland: report of 3 cases with marked apocrine differentiation.

Low-grade intraductal carcinomas (LG-IDCs) of salivary gland are rare neoplasms that resemble atypical ductal hyperplasia or LG-IDCs of the breast. They have been referred to as "low-grade salivary duct carcinomas" or "low-grade cribriform cystadenocarcinomas." Herein, we describe 3 additional cases of LG-IDCs, 2 were pure intraductal carcinomas, although 1 demonstrated increasing cytologic atypia and progression to an invasive adenosquamous carcinoma. The latter had been present for 7 years before demonstrating clinical and pathologic progression to a widely invasive malignancy. The intraductal component in all cases exhibited a remarkable degree of apocrine differentiation. The tumor cells were positive for AE1:AE3, Cam 5.2, high molecular weight keratin, CK7, CK19, BRST-2, and androgen receptors (ARs). S-100 was positive in 2 cases and negative in 1 case. The intraductal neoplastic cells were surrounded by myoepithelial cells positive for CK14, actins, calponin, high molecular weight keratin, and p63. All the tumors were negative for CK20, estrogen and progesterone receptors, Her2Neu, and p53. Extensive apocrine differentiation, expression of ARs, CK7, and CK19, and progression to a widely invasive carcinoma after a long clinical latency have not been reported in LG-IDCs previously. These tumors share some histopathologic features with salivary duct carcinoma including apocrine differentiation, and expression of ARs and BRST-2. The terms "low-grade salivary duct carcinomas" and "low-grade cribriform cystadenocarcinomas" should be abandoned in favor of LG-IDC of salivary gland, which better reflects their predominantly noninvasive, intraductal nature.