Benign Sclerosing Lesion of Salivary Gland Dr. Ben Pilch

Diagnosis: Benign sclerosing lesion of salivary gland (?sclerosing pleomorphic adenoma [sclerosing adenosis-like pleomorphic adenoma], ?sclerosing adenosis). Slide 1 Click to view with ImageScope Click to view with a Web-Based Viewer The submitted slide shows a cellular tumorous mass with a dense fibrotic stroma. In one portion of the tumor, the lesion resembles a cellular pleomorphic adenoma with a fibrotic rather than a myxochondroid stroma. Thus, there are multiple small ductules containing eosinophilic intraluminal material, lined by a layer of myoepithelial cells. An unusual feature of the lesion is that extending outward and peripherally from this area are narrow strands of cells, sometimes forming narrow tubules and at times seeming to represent strands of single cells. These strands and narrow tubules are arrayed in an infiltrative-appearing pattern in the dense fibrous stroma. In areas, the strands are present in close proximity to nerve structures. On close examination, the tumor cells are cytologically bland, mitoses appear scant, if present, and necrosis is absent. One diagnostic possibility that presents itself is that of an infiltrating well-differentiated adenocarcinoma of the salivary gland. However, there is a focal resemblance to pleomorphic adenoma, and, in addition, the strands and narrow tubules appear compressed, perhaps by the fibrous stroma, and a striking resemblance to sclerosing adenosis of the breast can be appreciated. Furthermore, the tumor cells do not infiltrate beyond the tumor's own fibrotic stroma into adjacent salivary gland tissue, and the tumor near the nerve does not exhibit true perineural invasion (i.e. presence of tumor within or inside the perineurium). Immunohistochemical studies show that these narrow strands and tubules are composed of an inner epithelial layer, positive for keratin and negative for actin and p63, and an outer myoepithelial layer, positive for actin, p63, and keratin. The histologic appearance and immunophenotype support the interpretation that this is a benign process of pseudoinfiltrative ductular structures rather than a malignant neoplasm containing truly infiltrative ductules devoid of a delimiting myoepithelial layer. The parotid resection, which was followed by radiation therapy, was performed in 1994 and, as of 2003, there has been no history of recurrence of the parotid tumor. A pulmonary adenocarcinoma was resected in 2003, but the histology did not resemble the parotid lesion. The lesion is therefore interpreted as representing a benign sclerosing lesion of the salivary gland, a sclerosing variant of pleomorphic adenoma (sclerosing adenosis-like pleomorphic adenoma) or perhaps sclerosing adenosis itself rather than a neoplasm. The current lesion has features in common with focal areas in some cases of sclerosing polycystic adenosis (SPA) of the salivary gland [1, 2]. Areas in some of the tumors reported by Gnepp et al resemble the sclerosing adenosis-like areas in the present lesion as well as sclerosing adenosis of the breast [1]. The cystic structures characteristic of SPA, however, are not present in the current case. SPA is currently considered to be a sclerosing inflammatory proliferative lesion analogous to polycystic change in the breast, rather than a neoplasm. The case presented here appears non-inflammatory with features reminiscent of pleomorphic adenoma, and the fibrotic tissue is interpreted as possibly representing tumor stroma. Whether this lesion represents a neoplasm and a variant of pleomorphic adenoma or a case of sclerosing adenosis of the parotid gland (a condition not previously described, to my knowledge) is an issue not completely resolved at this point, in my opinion. The important issue is not to confuse this fascinating lesion with an infiltrative adenocarcinoma. References Gnepp DR, Wang LJ, Brandwein-Gensler M, Slootweg P, Gill M, Hille J. Sclerosing polycystic adenosis of the salivary gland. A report of 16 cases. Am J Surg Pathol 2006; 30: 154-164. Smith BC, Ellis GL, Slater LJ, Foss RD. Sclerosing polycystic adenosis of major salivary glands. A clinicopathologic analysis of nine cases. Am J Surg Pathol 1996; 20: 161-170.