Serous effusion cytology of extranodal natural killer/T-cell lymphoma

Extranodal natural killer/T-cell lymphoma, nasal type (ENKTCL-N), is a rare form of lymphoma that typically occurs at extranodal sites. It is one of the most common extranodal lymphomas in China. Literature on effusions and cytological findings relating to ENKTCL-N is limited. We studied five consecutive cases of ENKTCL-N effusions collected over a 3-year period. The cytomorphological, immunocytochemical and molecular biological features were evaluated with literature review. The purpose of this study is to discuss how to diagnose ENKTCL-N cytologically in effusions.

Smears and cell block sections were reviewed for each case. Immunocytochemistry was performed on 4-μm paraffin sections. Antibodies used were as follows: cCD3 (intracytoplasmic CD3), CD45RO, surface CD3, CD20, CD79a, CD56, TIA-1, granzyme B, CD30, CD99, TdT and Ki-67. In situ hybridization for EBER1/2 (EBER-ISH) and T-cell receptor γ (TCRγ) gene rearrangement were performed for all cases.

Large to medium-sized tumour cells with pleomorphic nuclei and coarse chromatin were found in a necrotic background in all cases. The cytoplasm of the tumour cells was scant to moderately abundant with occasional cytoplasmic projections; in Giemsa-stained smears, fine granules were present in some tumour cells. Mitotic figures were frequent. The tumour cells were all positive for CD56, granzyme B, TIA-1 and cCD3, and were negative for surface CD3, CD20 or CD79a, CD99 and TdT. The MIB index was 50-80%. Epstein-Barr virus-encoded RNA (EBER) hybridizing signals were detected for most neoplastic cells. The T-cell receptor gamma gene rearrangement analysis showed germ-line configuration, except for one case.

Effusion cytology may be appropriate for establishing the diagnosis of ENKTCL-N, particularly for patients in whom tissue biopsy is not possible.