Reactivity With TdT in Merkel Cell Carcinoma: Potential Diagnostic Pitfall
By Cary J. Buresh, M.D., Bahram Robert Oliai, M.D., Rodney T. Miller, M.D.
Merkel cell carcinoma (MCC) is a high-grade neuroendocrine carcinoma of skin characterized by cells with a “blastic” appearance, scant cytoplasm,and fine, evenly distributed chromatin. Terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase present in thymic T cells, lymphoblastic lymphoma/leukemia, and some cases of acute myeloid leukemia. After observing TdT immunoreactivity in a case of MCC, we analyzed 26 tumors by immunohistochemical analysis to determine their spectrum of reactivity with TdT and identified TdT in 19 (73%) of 26 MCCs.