Answer: Low grade cribriform cystadenocarcinoma

Histology: The cellular proliferation is primarily confined to cysts and adjacent ducts. The intraductal proliferation forms micropapillae and cribriforming structures bears a striking resemblance to proliferative breast disease ranging from florid ductal hyperplasia to atypical duct hyperplasia. The cells are uniform and bland with finely dispersed chromatin and small nucleoli. They lack pleomorphism, a high mitotic rate, and necrosis.

Discussion: The WHO classification of salivary gland tumors now recognizes an entity referred to a low-grade cribriform cystadenocarcinoma (LGCCC). The rare cystic carcinoma was formerly referred to as low-grade salivary duct carcinoma. It shares with salivary duct carcinoma a pattern of growth that is striking resemblance to proliferative breast disease, but it occupies the lower end of the proliferative spectrum. While salivary duct carcinoma looks a lot like intraductal comedo carcinoma, LGCCC spans the spectrum of intraductal papilloma to atypical duct hyperplasia to low-grade cribriforming intraductal carcinoma. The cells tend to be bland, and there is an absence of tumor necrosis, anaplasia and a high mitotic rate.

LGCCC is morphologically similar to cystadenoma and cystadenocarcinoma. Distinguishing features of LGCCC include the presence of a more florid intracystic proliferation with solid areas, the striking resemblance of this proliferation to atypical hyperplasia and carcinoma in-situ of the breast, and the presence of the golden brown intracellular pigment (not well developed in the present case).

LGCCC is a low-grade carcinoma. These tumors do not generally recur or behave in an aggressive fashion following surgical removal, but cases have been few in number and follow-up limited.