Identification of T-cell receptor expression in EBV-positive neoplastic cells in extranodal NK/T-cell lymphoma, nasal-type, and comparison with T-cell receptor gene rearrangement by BIOMED-2 assay

The cellular lineage of extranodal NK/T-cell lymphoma, nasal-type (ENKTL), is determined by expression of T-cell receptor (TR) or TR gene rearrangement. In ENKTL, from TR immunohistochemistry, it may often be difficult to decide whether TR-positive cells are tumor cells or not, especially when TR is expressed in a subset of tumor cells. To analyze TR expression pattern and TR rearrangement in T-lineage ENKTL, we performed double immunofluorescence staining for Epstein-Barr virus-encoded small RNAs (EBER)/T-cell receptor (TCR) βF1 and CD56/TCR βF1 in 12 cases of ENKTL that showed TCR βF1 expression in immunohistochemistry. TR gene rearrangement was analyzed using a commercial BIOMED-2 multiplex polymerase chain reaction system. Immunohistochemistry showed that all 12 cases expressed TCR βF1 in a wide range of infiltrating cells from 100% to <1%. Two of them expressed both TCR βF1 and TCR cγM1. EBER/TCR-βF1-positivity was confirmed in 10 cases by double staining. One case failed to show EBER/TCR-βF1-positive cells but showed a CD56/TCR βF1-positive result. Among 12 cases, 5 had poor-quality DNA, 3 of them showed no polymerase chain reaction product, and 2 cases showed nonspecific peak of low height. Five of 7 cases with good DNA quality demonstrated monoclonal TR gene rearrangement. Based on TR expression and TR gene rearrangement, 10 of 12 cases of ENKTL were decided as a T-lineage tumor. In conclusion, because of common TR silence and poor DNA quality, consideration of both immunohistochemistry and TR gene rearrangement is necessary to determine the lineage of ENKTL.