Coexistence of mucous retention cyst and basal cell adenoma arising from the lining epithelium of the cyst. Report of two cases.

OBJECTIVE To report 2 cases of coexisting mucous retention cyst and basal cell adenoma arising from the lining epithelium of the cyst. CLINICAL PRESENTATION AND INTERVENTION Two cases of painless swellings, well-demarcated, soft to palpation, and located in the submucosa of the upper lip were clinically examined with the provisional diagnosis of mucocele or salivary gland tumor. Histological examination showed the presence of a large unilocular cystic cavity in many parts surrounded by single or bilayered lining epithelium composed of flattened to cuboidal cells, and in other parts surrounded by projections of cells arranged in a trabecular pattern far into the cystic cavity. The trabeculae were composed of basal and low columnar cells that sometimes formed small duct-like structures. Immunohistochemistry showed that the lining epithelium of the cystic cavity and the cells of the projections expressed cytokeratin 7 and high-molecular-weight cytokeratins. The cells of the projections were weakly positive for S-100 protein and negative for vimentin and alpha-smooth muscle actin. Based on the results, a diagnosis of coexisting mucous retention cysts and basal cell adenomas arising from the lining epithelium of cysts was made. CONCLUSION The coexistence of mucous retention cysts and basal cell adenomas arising from the lining epithelium of the cyst is reported.