Differential Expression of p53 in Mycosis Fungoides, Sezary Syndromes, and Their Transformed Forms

Mycosis fungoides (MF) and Sezary syndrome (SS) are common entities among primary cutaneous lymphomas. Large cell transformation is challenging for diagnosis and therapy. Molecular mechanisms by which these lymphomas undergo this transformation are poorly defined. We studied the immunohistochemical status of p53 in these entities and assessed whether p53 expression could be a useful tool for diagnosis and assessment of transformation. We extracted patients with transformed and untransformed SS or MF from the French Study Group on Cutaneous Lymphoma database between 2014 and 2021, followed in the Rennes University Hospital. An immunohistochemical study of p53 expression was performed on the biopsies sampled as part of routine care. We compared p53 overexpression in the different groups. We included 25 patients with MF, 7 patients with transformed MF (T-MF), 11 patients with SS, and 5 patients with transformed SS (T-SS). Using a cut-off set at 30% expression of neoplastic cells, we noted an overexpression of p53 in T-MF and T-SS compared with nontransformed forms (47% vs. 12%, respectively, P < 0.01) and in MF compared with SS (23% vs. 7%, respectively, P < 0.01). Overexpression of p53 with a cut-off at 30% therefore seems to be a discriminating tool in the differential diagnosis of MF/SS versus their transformed forms as well as the differential diagnosis between MF and SS.