The sclerosing variant of adenoid cystic carcinoma. A previously unrecognized neoplasm of major salivary glands

We report 2 cases of a previously unrecognized sclerosing variant of adenoid cystic carcinoma (ACC) of major salivary glands. One of the tumors arose in the parotid and the other in the submaxillary gland of young adult patients. The tumors were composed predominantly of varying-sized large sclerotic and hypocellular nodules containing myoepithelial cells and pseudovascular spaces, most likely the result of artifactual retraction. In moderately cellular nodules, there were numerous small globules or spherules surrounded by myoepithelial cells similar to those of collagenous or mucinous spherulosis. Focal cribriform areas and ductal structures lined by epithelial cells were also identified. Both tumors showed perineural invasion. Electron microscopy revealed that both large nodules and small globules or spherules were composed of excessive amounts of basement membrane and thick-banded collagen fibers. The myoepithelial cells showed immunoreactivity for smooth muscle actin (SMA), S100 protein, and vimentin. Collagen IV showed variable reactivity in both the large nodules and small spherules. More cases of the sclerosing variant of ACC and long-term follow-up of the patients are needed to determine the biologic behavior of this unusual but distinctive variant of ACC.