Track: Clinical Studies

Abstract:

Immunohistochemistry with T-cell receptor β-chain constant domain 1 (TRBC1) has been reported to be helpful in distinguishing between a clonal or reactive process, limited by low tumor burden and high numbers of reactive T-cells. In cases of hypopigmented mycosis fungoides, neoplastic cells can be a relatively small proportion of the total T-cells present; therefore, we hypothesized that it may be more useful to specifically look at TRBC1 expression in intraepidermal lymphocytes. TRBC1 immunohistochemistry was performed and quantified retrospectively on four cases that were clinically suspicious for hypopigmented mycosis fungoides with known T-cell receptor clonality results by polymerase chain reaction. Monoclonality by immunohistochemistry was defined as monotypic-negative (TRBC1 < 25%, i.e. < 1 in 4 positive lymphocytes) or monotypic-positive (TRBC1 > 75%, i.e. > 3 of 4 lymphocytes positive), or nonclonal (TRBC1 >25% and <75%). Percentage of TRBC1-positive cells was compared with the number of lymphocytes in hematoxylin and eosin sections as well as CD3-positive and CD8-positive lymphocytes. Immunohistochemical results when assessing TRBC1 clonality in the intraepidermal component in all four cases were concordant with T-cell receptor clonality assays. Two cases demonstrated monotypic-positive TRBC1 expression (<20% and <5%) in the epidermis, and the other two were monotypic-negative (40% and 33%). Assessing TRBC1 expression with particular focus on the intraepidermal component may be helpful in determining clonality as a useful data point when evaluating for hypopigmented mycosis fungoides.

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Jessica Zhao