Nodal presentation of nasal-type NK/T-cell lymphoma. Report of two cases with fine needle aspiration cytology findings

BACKGROUND: Epstein-Barr virus (EBV)-associated NK/T-cell lymphoma typically occurs in extranodal sites, such as nasal cavity, nasopharynx, gastrointestinal tract, skin, testis and salivary gland. Secondary lymph node involvement is rarely encountered until late in the disease course. The fine needle aspiration cytology of NK/T-cell lymphoma with a nodal presentation has not been described before. CASES: Two cases of nasal-type (extranasal) NK/T-cell lymphoma with a nodal presentation were seen at Pamela Youde Nethersole Eastern Hospital, Hong Kong. Both patients presented with submandibular lymph node enlargement but unremarkable peripheral blood and bone marrow findings. Fine needle aspiration cytology was available in both cases, showing a heterogeneous population of small to medium-sized lymphoid cells, follicular center cells, plasma cells, eosinophils and some histiocytes. The medium-sized lymphoid cells showed readily discernible nuclear atypia with an irregular nuclear outline. Cell block sections revealed occasional lymphoid cells with pleomorphic nuclei. Immunocytochemical study confirmed the presence of CD56-positive lymphoma cells. In situ hybridization for EBV-encoded RNA also revealed positive nuclear signals. Histologic examination of the surgical biopsies showed interfollicular expansion by malignant lymphoid cells. Immunoglobulin heavy chain gene and T-cell receptor gene rearrangement studies demonstrated a germline pattern, confirming the putative NK (natural killer cell), non-B and non-T lineage of the lymphoma cells. CONCLUSION: Nodal presentation of NK/T-cell lymphoma, though rare, is diagnosable on the basis of fine needle aspiration biopsy alone, especially in view of its distinctive immunophenotype and EBV association. Recognition of the subtle but definite cytologic atypia of malignant lymphoid cells and presence of an appropriate background (including more eosinophils than usual), together with proper application of ancillary techniques, is crucial to arriving at a correct diagnosis.