The Value of Immunohistochemical Expression of TOX, ICOS, and GATA-3 in the Diagnosis of Mycosis Fungoides

Background:Mycosis fungoides (MF) is considered the commonest type of cutaneous T-cell lymphoma representing about 50% of all primary cutaneous lymphomas. Differentiation between MF and another inflammatory dermatitis (BIDs) is important to ensure proper management. Aim:We aimed to evaluate the immunohistochemical expression of TOX, ICOS, and GATA binding protein 3 (GATA-3) in early stages MF (stage IA and IB) to establish their diagnostic value and to guide the use of inhibitors in the treatment of cutaneous T-cell lymphomas. Materials and Methods:A retrospective study of 75 skin paraffin blocks (punch biopsy) 40 cases of MF and 35 cases of eczematous dermatitis as a group representing other inflammatory dermatitis were retrieved from archives of the pathology department of our University, during the period from October 2017 to May 2021. Results:About 98% and 90% of patients in the MF group had positive TOX and ICOS, while 70% of them had positive GATA-3. High expression of TOX, ICOS, and GATA-3 was associated with higher stages. Conclusions:TOX is considered a diagnostic marker for early MF. The importance of identifying novel markers in MF expressed by immunohistochemistry, such as ICOS, has been established. According to our results, GATA-3 could be used as an accessory marker in the diagnosis of MF when combined with TOX and ICOS in a panel.