A 48-Year-Old White Woman With a Nodular Mass in the Right Parotid Gland.
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Microscopic evaluation of the specimen showed heavy infiltration of lymphocytes within parotid gland parenchyma. A fragment of tissue was also submitted for flow cytometry, which was positive for CD45, DR, CD19, CD20, and CD24. Dual-parameter analysis demonstrated a population of CD19 bright monoclonal [Kappa] B cells (Figure 3).
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Pathologic Diagnosis: A Case of Malignant Lymphoma in Parotid Gland
Primary malignant lymphomas account for only 1.7% to 3.1% of all salivary gland neoplasms and 3% to 4% of all parotid gland tumors. Eighty-four percent to 97% of these tumors are of the non-Hodgkin type and are of B-cell origin, and the parotid gland is by far the most common site. The average age at detection is 63 years, and the ratio of affected females to males varies among studies, ranging from 0.5 to 2.3. However, concurrent autoimmune diseases, such as Sjogren syndrome, impart an increased risk for salivary gland lymphomas. In patients without existing autoimmune disease, the most common presentation is complaint of a unilateral, enlarging, painless mass.
Malignant lymphomas of the parotid gland may arise from the mucosa-associated lymphoid tissue (MALT) within the parenchyma, in intraglandular lymph nodes, in both, or from dissemination of an existing lymphoma. There are currently many interpretations for the terms primary and secondary in the literature. In this case, primary refers to a lymphoma that first presents in the parotid gland, while secondary refers to parotid involvement in a patient with documented malignant lymphoma. Other authors use the term primary to indicate origination in MALT rather than intraparenchymal lymph nodes, and still others define primary lymphomas as arising concurrently with an underlying autoimmune disorder.
At the time of diagnosis, the tumor is usually low- or intermediate-grade by the Working Formulation, and the patient is found to have Ann Arbor stage I or II disease. The most common types are follicular small cleaved, follicular mixed, and diffuse large cell lymphomas. Tumors of small lymphocytes are generally slow to progress and have a favorable long-term prognosis, with 52% to 83% survival at 5 years. Large cell variants are rapidly progressive and have a poor outcome/and those with Ann Arbor stage III or IV disease are more resistant to treatment. Overall, patients with malignant lymphomas of the parotid gland have a better prognosis than patients with non-Hodgkin lymphomas arising elsewhere. However, patients with concurrent Sjogren syndrome generally follow a rapidly fatal course.
Grossly, the tumor appears as a firm mass that is tan-white on cut section, similar to lymphomas arising in other sites. Microscopic evaluation reveals sheets of monomorphic, medium-sized lymphoid cells with bland nuclei. Further characteristics include occasional intranuclear inclusions, or Dutcher bodies; crush artifact; periductal fibrosis; and ductal metaplasia that resembles epimyoepithelial islands. Tumor cells frequently invade the epimyoepithelial islands, forming lymphoepithelial lesions. Epithelial complexes are gradually replaced by tumor. Transformation of low-grade MALT lymphomas to higher-grade large cell lymphomas has been observed. Immunohistochemistry commonly shows a B-cell phenotype with light-chain restriction and positivity for CD45RA and Bcl-2. The cells are also typically positive for CD20 and CD22, as well as pan-B-cell markers such as L26.
The differential diagnosis may include benign lymphoepithelial lesion, nonspecific sialadenitis, cystadenoma lymphomatosum papilliferum, nodal B-cell chronic lymphocytic lymphoma, mantle cell lymphoma, follicular lymphoma, and human immunodeficiency virus-related lymphadenopathy. Sialadenitis involves random collections of lymphocytes with occasional neutrophil involvement, and there is usually no distortion of tissue architecture. Benign lymphoepithelial lesions frequently contain germinal centers, and involved lymphocytes lack the cellular features mentioned above. Furthermore, diagnosis of lymphoma is strengthened by demonstration of epimyoepithelial complexes with infiltrating monocytoid B cells and lymphoid infiltration of surrounding fibroadipose tissue or perineural spaces. Cystadenoma lymphomatosum papilliferum is characterized grossly by multicystic spaces, and microscopic examination reveals a polyclonal lymphocytic population with interspersed T cells, mast cells, and dendritic cells. Large epithelial cells cover the surface, and some of the cells may be ciliated. Human immunodeficiency virus-related lymphadenopathy frequently shows follicle lysis within the lymphoid tissue, involving movement of mantle lymphocytes into the germinal centers. The disruption of the follicular centers, giving it a "moth-eaten appearance," is common and useful, but is not diagnostic. Other neoplasms of lymphoid tissue may be distinguished by flow cytometry. Demonstration of monotypic immunoglobulin light chains is diagnostic.
Therapy includes surgical resection and radiotherapy, chemotherapy, or both. The involvement of Epstein-Barr virus or human herpesvirus 6 has been suggested. Interestingly, the t(11;18)(q21;q21) chromosome translocation has recently been associated with low-grade malignant non-Hodgkin lymphomas of MALT, introducing a potential predictive value? It has also been shown that MALT lymphomas lack rearrangements of the bcl-2 gene (t[14; 18]).
[1.] Barnes L, Myers EN, Prokopakis EP. Primary malignant lymphoma of the parotid gland. Arch Otolaryngol Head Neck Surg. 1998;124:573-577.
[2.] Ellis GL, Auclair PL. Tumors of the Salivary Glands. Washington, DC: Armed Forces Institute of Pathology; 1997. Atlas of Tumor Pathology; 3rd series, fascicle 17.
[3.] Mehle ME, Kraus DH, Wood BG, et al. Lymphoma of the parotid gland. Laryngoscope. 1993; 103(1 pt 1): 17-21.
[4.] Rosai J. Ackerman's Surgical Pathology. St Louis, Mo: Mosby-Year Book Inc; 1996:827-828, 842-843.
[5.] Ott G, Katzenberger T, Greiner A, et al. The t(11; 18)(q21; q21) chromosome translocation is a frequent and specific aberration in low-grade but not high-grade malignant non-Hodgkin's lymphomas of the mucosa-associated lymphoid tissue (MALT-) type. Cancer Res. 1997;57:3944-3948.
Accepted for publication April 19, 2000.
From the Department of Pathology, Medical College of Ohio, School of Medicine, Toledo, Ohio.
Reprints not available from the author.
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|Author:||Sheridan, Todd; Islam, Shahidul; Zaher, Aiman|
|Publication:||Archives of Pathology & Laboratory Medicine|
|Date:||Feb 1, 2001|
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