CD4 and CD8 double-negative immunophenotype of thymoma-associated lymphocytes in a dog. (November 2020)

• Record Type: Journal Article
• Authors: Wikander, Yvonne M.; Knights, Kaori; Coffee, Calli; Vernau, William; Biller, David S.; Higginbotham, Mary Lynn; Springer, Nora L.
• Is Part Of: Journal of veterinary diagnostic investigation. Volume 32:Number 6(2020:Nov.)
• Page Start: 918
• Page End: 922
• Publication Date: 2020-11
• Subjects: dogs -- flow cytometry -- immunophenotype -- lymphocytosis -- PCR for antigen receptor gene rearrangement -- thymoma; Veterinary medicine -- Diagnosis -- Periodicals; 636.0896075
• DOI: 10.1177/1040638720948628
• Languages: English
• ISSNs: 1040-6387

Abstract

Persistent small-cell lymphocytosis in dogs with a concurrent mediastinal mass has been associated with both thymoma and small-cell lymphoma. In thymomas, neoplastic thymic epithelial cells induce overproduction and release of polyclonal lymphocytes, whereas thymic lymphoma results in thymic effacement by a clonal expansion of neoplastic lymphocytes and subsequent leukemic phase of lymphoma. Flow cytometry has been used to differentiate these 2 entities by immunophenotyping mediastinal mass aspirates. It has been reported that cases with mediastinal masses in which ≥ 10% of the associated small-cell lymphocytes were double positive for CD4 and CD8 were thymomas, whereas masses associated with < 10% were suggestive of lymphoma. We report a unique case of thymoma-associated lymphocytosis lacking the classic CD4+CD8+ immunophenotype. Our findings suggest that there may be more diversity in the thymoma-associated lymphocyte immunophenotype than has been identified previously; immunophenotyping alone might not be sufficient to differentiate thymic small-cell lymphoma from thymoma-associated lymphocytosis. In dogs with mediastinal masses and peripheral lymphocytosis, employing a variety of testing modalities to avoid misdiagnosis is prudent. These modalities include cytologic and/or histologic evaluation, immunophenotyping, and clonality assessment.