Comparison of 2 T-Cell Receptor-γ Clonality Assays on Skin Biopsies Suspicious for Mycosis Fungoides

PCR-based fragment analysis of the T-cell receptor (TCR) gene is used extensively in diagnostic labs to assess clonality in T-cell populations in multiple tissue sites. Of the numerous TCR assays that have been reported, studies assessing use on biopsies suspicious for mycosis fungoides specifically are lacking. We compared clonality findings from a previously run 2-tube/2-fluorochrome dye assay to a redesigned 1-tube/1-fluorochrome dye assay on formalin-fixed skin biopsies. Overall, the accuracy of the 2-tube assay was marginally better (75.7% vs. 71.4%), when using clinical history combined with histologic diagnosis as the gold standard. The 2-tube assay had better sensitivity (73.7% vs. 65.8%), while the 1-tube assay had superior specificity (93.8% vs. 87.5%). Clonality results were easier to interpret with the 1-tube assay. In nearly 19% of cases, a change of assays on the same biopsy resulted in a change of clonality interpretation. For laboratories that change TCR-γ clonality assays, follow-up biopsies for mycosis fungoides assessment may result in a change of diagnosis.