Lymphomas and benign lymphoepithelial lesion
Lymphomas of the major salivary glands are characteristically of the non-Hodgkin type. In an AFIP review of case files, non-Hodgkin lymphoma accounted for 16.3% of all malignant tumors that occurred in the major salivary glands; disease in the parotid gland accounted for about 80% of all cases.
Patients with benign lymphoepithelial lesion (e.g., Mikulicz disease), which is a manifestation of the autoimmune disease, Sjögren syndrome, are at an increased risk for development of non-Hodgkin lymphoma.[80,81,82,83,84] Benign lymphoepithelial lesion is clinically characterized by diffuse and bilateral enlargement of the salivary and lacrimal glands. Morphologically, a salivary gland lesion is composed of prominent myoepithelial islands surrounded by a lymphocytic infiltrate. Germinal centers are often present in the lymphocytic infiltrate. Immunophenotypically and genotypically, the lymphocytic infiltrate is composed of B-lymphocytes and T-lymphocytes, which are polyclonal. In some instances, the B-cell lymphocytic infiltrate can undergo clonal expansion and evolve into frank non-Hodgkin lymphoma. The vast majority of the non-Hodgkin lymphomas arising in a background of benign lymphoepithelial lesions are marginal zone lymphomas of mucosa-associated lymphoid tissue (MALT).[81,82,83,84] MALT lymphomas of the salivary glands, like their counterparts in other anatomic sites, typically display relatively indolent clinical behavior.[3,85]
Primary non-MALT lymphomas of the salivary glands may also occur and appear to have a prognosis similar to those in patients who have histologically identical nodal lymphomas.[86,87] Unlike non-Hodgkin lymphoma, involvement of the major salivary glands by Hodgkin lymphoma is rare. Most tumors occur in the parotid gland. The most common histologic types encountered are the nodular sclerosing and lymphocyte-predominant variants.[88,89]
Mesenchymal neoplasms account for 1.9% to 5% of all neoplasms that occur within the major salivary glands.[90,91] These cellular classifications pertain to major salivary gland tumors. Because the minor salivary glands are small and embedded within fibrous connective tissue, fat, and skeletal muscle, the origin of a mesenchymal neoplasm from stroma cannot be determined. The types of benign mesenchymal salivary gland neoplasms include hemangiomas, lipomas, and lymphangiomas.
Malignant mesenchymal salivary gland neoplasms include malignant schwannomas, hemangiopericytomas, malignant fibrous histiocytomas, rhabdomyosarcomas, and fibrosarcomas, among others; in the major salivary glands, these neoplasms represent approximately 0.5% of all benign and malignant salivary gland tumors and approximately 1.5% of all malignant tumors.[90,92,93] Of importance is to establish a primary salivary gland origin for these tumors by excluding the possibilities of metastasis and direct extension from other sites. In addition, the diagnosis of salivary gland carcinosarcoma should be excluded. Primary salivary gland sarcomas behave like their soft tissue counterparts in which prognosis is related to sarcoma type, histologic grade, tumor size, and stage.[93,94] (Refer to the PDQ summary on Adult Soft Tissue Sarcoma Treatment for more information.) A comprehensive review of salivary gland mesenchymal neoplasms can be found elsewhere.