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Comments regarding high scatter T cells in cutaneous T cell lymphoma
Submit responseTo the Editor:
It was with interest that we recently read the article by Clark et. al. The authors nicely demonstrate that T cells with high side angle light scatter by flow cytometry are clonal and represent the neoplastic CTCL cells from skin biopsy specimens. We previously had reported this finding in 20071 and have indicated the phenomenon in two additional reviews2-3. It was not, however, the focus of our study of CTCL skin biopsy specimens by flow cytometry. Moreover we used CD45 vs side angle light scatter gating to identify the neoplastic cells in many of our cases. Our specimens were analyzed directly ex vivo from the patient and not cultured as was the case in the Clark's study. It should be noted that in some instances there is little difference in CD45 expression or side angle light scatter of neoplastic CTCL cells from normal T cells and it should be stressed that neoplastic cells cannot always be separated from normal T lymphocytes using side angle light scatter and/or CD45 expression. Additionally, as the authors have indicated, virally activated T cells, particularly CD8 T cells in EBV infection, may demonstrate high side angle light scatter which can lead to a diagnostic confusion and misinterpretation of a reactive process as neoplastic.
In our study, we documented phenotypic expression abnormalities on the neoplastic cells and noted that the neoplastic cells comprise, on average 25% of all lymphocytes recovered for flow cytometry. In some cases the neoplastic cell population was significantly less. Therefore, studies relying solely on immunohistochemistry to identify the neoplastic cell phenotype can be fraught with difficultly.
We would like to make one last point. The identification of neoplastic lymphoid cells using light scatter is certainly not unique to evaluation of skin biopsy specimens for CTCL as other lymphoma cells isolated from tissue biopsy specimens, particularly large B cell lymphomas, demonstrate the same phenomenon. Clinical flow cytometrists have been aware of this characteristic for many years4-5. Nonetheless, it is important to re-emphasize this concept since it is an important tool for the diagnosis and evaluation of lymphomas, particularly skin biopsy specimens that may harbor a CTCL. I therefore applaud the authors for bringing this property of the neoplastic T cells in CTCL to the fore.
References:
1. Oshtory S, Apisarnthanarax N, Gilliam AC, Cooper KD, Meyerson HJ. Usefulness of flow cytometry in the diagnosis of mycosis fungoides. J Am Acad Dermatol. 2007;57(3):454-62
2. Meyerson HJ. Flow cytometry for the diagnosis of mycosis fungoides. G Ital Dermatol Venereol. 2008;143(1):21-41.
3. Meyerson HJ. A practical approach to the flow cytometric detection and diagnosis of T-cell lymphoproliferative disorders. Lab Hematol. 2010;16(3):32-52.
4. Sun T, Sangaline R, Ryder J, Gibbens K, Rollo C, Stewart S, Rajagopalan C. Gating strategy for immunophenotyping of leukemia and lymphoma and Leukemia. Am J Clin Pathol. 1997;108(2):152-7.
5. Ichinohasama R, DeCoteau JF, Myers J, Kadin ME, Sawai T, Ooya K Three-color flow cytometry in the diagnosis of malignant lymphoma based on the comparative cell morphology of lymphoma cells and reactive lymphocytes. Leukemia. 1997;11(11):1891-903.
Conflict of Interest:
None declared
