%0 Journal Article %J Polish Journal of Pathology %@ 1233-9687 %V 73 %N 2 %D 2022 %F Pęksa2022 %T Diagnostically misleading aberrant terminal deoxynucleotidyl transferase expression in germ cell tumors %X Terminal deoxynucleotidyl transferase (TdT) is a unique type of DNA polymerase predominantly expressed in precursor lymphoid cells and acute lymphoblastic leukemia. It participates in the junctional diversity of T-cell receptors and immunoglobulins. Recently, aberrant TdT expression was found in seminomas. Here, we evaluated the expression of TdT in our cohort of germ cell tumors (GCTs) with two anti-TdT antibody clones. We included 173 cases of testicular GCTs, 5 ovarian dysgerminomas, and one gonadoblastoma in the study. Tissue microarrays containing representative tumor samples were constructed and subsequently stained with anti-TdT monoclonal rabbit antibody EP266 (Dako) and TdT rabbit polyclonal antibody (Cell Marque). Expression was assessed with the H-score. No specific nuclear reaction was observed for the polyclonal anti-TdT antibody. The H-score values varied between the histological subtypes for the EP266 antibody. Positive nuclear staining was consistently seen in germ cell neoplasia in situ , seminoma, dysgerminoma, and embryonal carcinoma. Pure tumors had higher TdT H-scores than the mixed ones. Teratomas, yolk sac tumors, and choriocarcinomas were almost uniformly negative. Our study confirms that aberrant expression of TdT by testicular and ovarian GCTs exemplifies a potential diagnostic pitfall in histopathological diagnostics. %A Pęksa, Rafał %A Kunc, Michał %A Bieńkowski, Michał %A Popęda, Marta %A Biernat, Wojciech %P 159-165 %9 journal article %R 10.5114/pjp.2022.120098 %U http://dx.doi.org/10.5114/pjp.2022.120098