Flow cytometric immunophenotyping is of great value to diagnosis of natural killer cell neoplasms involving bone marrow and peripheral blood.

Natural killer (NK) cell neoplasms are unusual disorders. In this study we compared results of flow cytometric immunophenotype (FCI) with cytomorphology, histopathology and clinical findings in a series of patients with NK cell neoplasms with peripheral blood and/or bone marrow involvement, and the FCI of neoplastic and normal NK cells were compared. Retrospective data and specimens (bone marrow aspiration or peripheral blood) from 71 cases of NK cell neoplasms were obtained. All patients have been demonstrated laboratory and clinical features consistent with NK cell neoplasms, and the subtypes were determined by integrated clinical estimation. Routine 4-color flow cytometry (FCM) using a NK/T cell related antibody panels was performed. NK cell neoplasms were divided into two major subtypes by FCI, namely malignant NK cell lymphoma, including extranodal nasal type NK cell lymphoma (ENKL, 11 cases) and aggressive NK cell lymphoma/leukemia (ANKL, 43 cases), and relative indolent chronic lymphoproliferative disorder of NK cell (CLPD-NK, 17 cases). The former exhibited stronger CD56-expressing, larger forward scatter (FSC) and more usually CD7- and CD16-missing. FCI of CLPD-NK was similar to normal NK cells, but CD56-expressing was abnormal, which was negative in five cases and partially or dimly expressed in eight cases. Cytomorphologic abnormal cells were found on bone marrow slides of 4 cases of ENKL and 30 cases of ANKL. Eight cases of ENKL were positive in bone marrow biopsies, and other three cases were negative. In 32 cases of ANKL which bone marrow biopsies were applied, 21 cases were positive in the first biopsies. Lymphocytosis was found only in six cases of CLPD-NK by cytomorphology, and biopsy pathology was not much useful for diagnosing CLPD-NK. These results suggest that FCM analysis of bone marrow and peripheral blood was superior to cytomorphology, bone marrow biopsy, and immunohistochemistry in sensitivity and early diagnosis for ANKL, stage III/IV ENKL and CLPD-NK. FCI could not only define abnormal NK cells but also determine the malignant classification. It is beneficial for clinical management and further study of NK cell neoplasms.