CD4 and CD8 double-negative immunophenotype of thymoma-associated lymphocytes in a dog

Yvonne M. Wikander, Kaori Knights, Calli Coffee, William Vernau, David S. Biller, Mary Lynn Higginbotham, Nora L. Springer

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)918-922
Number of pages5
JournalJournal of Veterinary Diagnostic Investigation
Issue number6
StatePublished - Nov 1 2020


  • dogs
  • flow cytometry
  • immunophenotype
  • lymphocytosis
  • PCR for antigen receptor gene rearrangement
  • thymoma

ASJC Scopus subject areas

  • veterinary(all)


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