Background: Mycosis fungoides (MF) is the most common type of cutaneous T-cell lymphoma (CTCL).
Differentiation of MF especially early stages (eMF) from its benign mimickers is important to ensure proper
management. TOX is a critical regulator of early T-cell development in the thymus that is considered as a useful
marker for MF diagnosis and prognosis.
Objective: The aim of the current study was to evaluate the ability of molecular marker TOX protein in diagnosis
of eMF, and its ability to differentiate eMF from similar benign inflammatory skin diseases (BIDs).
Methodology: This is a case control study and was carried out on 60 subjects; 20 patients as eMF, 20 patients as
(BIDs) and 20 normal skin specimens as control cases. The diagnosis was established after clinicopathological
correlation. Immunohistochemistry (IHC) was done for MF, BIDs and normal skin cases for TOX and CD4 IHC
stains.
Results: TOX expression showed a significant positive expression in MF cases compared to BIDs and control
groups, with 100% sensitivity and 95% specificity. The pattern of TOX IHC stain in MF was diffuse, while in BIDs
was focal.
Conclusion: TOX might be considered a diagnostic marker for eMF that can differentiate eMF from BIDs
mimickers.