Value of TOX Immunoexpression in the Diagnosis of Early Mycosis Fungoides

Background: The lack of a specific marker to differentiate malignant from reactive T-cells makes a definite diagnosis difficult in patients suspected of having mycosis fungoides. This study has evaluated value of thymocyte selection-associated high mobility group box factor expression in the differentiation of early mycosis fungoides from a benign inflammatory dermatosis. Methods: We selected 22 mycosis fungoides cases, 18 cases suspicious for mycosis fungoides, and 12 cases of eczematous dermatitis from patients who attended Dermatology Clinic, Shiraz University of Medical Sciences (2008-2015). The obtained skin biopsies were immunostained for thymocyte selection-associated high mobility group box factor antigen in addition to pan T cell markers. The slides were evaluated for the percentage of tumor cells and intensity of immunoreactivity. Results: From 22 cases of mycosis fungoides, 40.9% showed massive infiltration of thymocyte selection-associated high mobility group box factor-positive lymphocytes (>30%) with high (3+) intensity in the epidermis; there was no case negative for thymocyte selection-associated high mobility group box factor expression. Only one eczematous dermatitis case had expression of thymocyte selection-associated high mobility group box factor-positive lymphocytes (>30%) with high intensity and 4 cases were negative for thymocyte selection-associated high mobility group box factor expression. The frequency of thymocyte selection-associated high mobility group box factor expressing lymphocytes was higher in biopsies from mycosis fungoides compared to eczematous dermatitis (P<0.05). CD7- cases expressed more thymocyte selection-associated high mobility group box factor-positive lymphocytes in the dermis and epidermis, which were significantly correlated (P=0.013). Conclusion: Thymocyte selection-associated high mobility group box factor, as a positive marker, in combination with pan T cell markers (especially CD7-) can be useful to detect mycosis fungoides malignant lymphoid cells.