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.