Track: Clinical Studies

Abstract:

Histopathologic evaluation of cutaneous T-cell lymphomas (CTCL) can be challenging, often requiring ancillary testing and clinicopathologic correlation. Immunohistochemistry for T-cell Receptor β Constant 1 (TRBC1) may be utilized as a surrogate marker for T-cell clonality in atypical T-cells present in specific cutaneous compartments. We assessed the utility of TRBC1 immunohistochemistry in folliculotropic mycosis fungoides (FMF) compared to various non-neoplastic conditions. TRBC1/CD3 dual stain was performed on 21 cases of FMF and 27 cases of reactive dermatitides. The approximate percentage of TRBC1-positive T-cells was assessed in the epidermis, follicular epithelium, and dermis. Less than 25% and greater than 75% staining for TRBC1 were considered monotypic patterns; between 25% to 75% staining was considered polytypic pattern. A monotypic pattern was observed in the epidermis in 10 of 13 (77%) FMF biopsies with epidermal infiltrate, compared to 3 of 16 (19%) non-neoplastic cases (p<0.05). Within the follicular epithelium, 13 of 21 (62%) FMF cases showed a monotypic pattern, compared to 7 of 16 (44%) non-neoplastic cases (p>0.05). All cases demonstrated a polytypic pattern in the dermis. Of note, 3 FMF cases showed greater than 75% TRBC1-positive T-cells; none of the non-neoplastic cases showed this pattern. TRBC1 immunohistochemistry was concordant with T-cell receptor gene rearrangement molecular results in 11/20 cases and showed a monotypic pattern in an additional 6/20 cases with negative or equivocal molecular studies. Our results suggest that TRBC1 immunohistochemistry is helpful in identifying clonal T-cell populations in CTCL and can be used in conjunction with other studies for accurate diagnosis.