P63 Expression in Primary Mediastinal Lymphomas

p63 protein is frequently used as an immunohistochemical marker in the pathologic diagnosis of non-hematological solid tumors. In malignant lymphoproliferative disorders, Primary mediastinal large B-cell lymphoma (PMLBCL) and classic Hodgkin lymphoma (CHL) represent two major types of mature B-cell lymphoma of the mediastinum. They have morphological and phenotypic overlap features, making this differential diagnosis challenging. This study aims to evaluate the diagnostic utility of p63 immunohistochemistry (IHC) in distinguishing these entities. In this single-center retrospective cohort study, we analyzed p63 expression using a tissue microarray approach in 44 cases of PMLBCL, 15 CHL cases and 7 Grey Zone Lymphoma (GZL). Diagnoses were made by experienced pathologists familiar with the nuances of lymphoma diagnosis, alongside clinical, morphological and immunohistochemical information. P63 expression was correlated with clinicopathological features. P63 nuclear expression was found in 26/44 (59%) cases of PMLCBL, followed by only 4/7 cases of GZL and 1/15 cases CHL. For PMLBCL, p63 demonstrated a sensitivity of 59%, specificity of 77%, a positive predictive value (PPV) of 83%, and a negative predictive value (NPV) of 49.7%. Survival analysis revealed no significant differences in metastasis-free survival based on p63 expression across PMLBCL, CHL, and GZL. These findings demonstrates that p63 has potential diagnostic value in differentiating PMLBCL from CHL and may be used as a potential tool in diagnosis of thoracic lymphoma. However, It has no prognostic value.