Immunohistochemical Evaluation of GATA3 Expression in Patch-Stage Mycosis Fungoides (MF) Compared With Benign Inflammatory Dermatoses (BID).

The histopathologic distinction between patch-stage mycosis fungoides (MF) and benign inflammatory dermatoses (BID) remains a persistent diagnostic challenge, often due to overlapping clinical and immunophenotypic features. GATA binding protein 3 (GATA3), a transcription factor critical in T-helper 2 cell differentiation, has emerged as a potential immunohistochemical marker in T-cell neoplasms. This study aimed to evaluate GATA3 expression in patch-stage MF compared with BID to assess its diagnostic value. Sixty formalin-fixed, paraffin-embedded skin biopsies were retrospectively analyzed, including 30 cases of patch-stage MF and 30 cases of BID (psoriasis, chronic dermatitis, and lichen planus). Immunohistochemical staining for GATA3 was performed, and lymphocytic nuclear staining was assessed in dermal and epidermal compartments. GATA3 expression > 50% in dermal lymphocytes was observed in 20% of MF cases and 6.7% of BID cases, yielding high specificity (93.3%) but low sensitivity (20%) for MF diagnosis. Epidermal GATA3 expression was uniformly low across both groups. No significant correlations were found between GATA3 expression and key histopathologic or immunophenotypic features of MF. Although elevated dermal GATA3 expression may support the diagnosis of MF in some cases, its substantial overlap with BID and low sensitivity limit its utility as a reliable standalone diagnostic marker for early-stage MF. GATA3 can be incorporated into broader immunohistochemical panels alongside more specific markers to improve diagnostic accuracy.