Validity of Immunohistochemical Expression of Cell Adhesion Molecule 1 (CADM1) in Differentiating Early-Stage Mycosis Fungoides from Its Benign Mimickers

Background: Mycosis fungoides (MF) is the commonest cutaneous T-cell lymphoma. Early-stage MF is difficult to be differentiated from benign inflammatory dermatoses (BIDs). CADM1 immunohistochemical staining may be valuable in differentiating early-stage MF from BIDs. Few studies are available regarding its role in this differentiation. Aim: To evaluate validity of CADM1 versus TOX & CD4 IHC in differentiating Early-Stage Mycosis Fungoides from Its Benign Mimickers. Materials and methods: This retrospective cross-sectional analysis was conducted of a total 75 paraffin blocks of skin tissue that were taken from seventy five individual from the pathology department's archives at faculty of medicine in Zagazig. thirty five blocks with MF and forty blocks with other benign dermatoses (15 cases of psoriasis, 15 lichen planus, 10 chronic dermatitis). CADM1, TOX and CD4 expressions were assessed. Results: Regarding the diagnostic performance of CADM1, TOX &CD4 in diagnosis of early stage MF and differentiating it from BIDs , we detected that CADM1 had the highest sensitivity (94.3%) followed by TOX (88.57%). While TOX had highest specificity (95%) followed by CADM1 (92.5%). Additionally, our study revealed that positive TOX expression was higher in plaque stage than in patch stage. Conclusion: CADM1 and TOX are considered beneficial in diagnosis of early MF, as CADM1 has highest sensitivity & TOX has highest specificity. TOX can also be used as prognostic marker being significantly higher in plaque than patch stage MF.