Flow cytometry as an accurate tool to complement fine needle aspiration cytology in the diagnosis of low grade malignant lymphomas.

OBJECTIVE Diagnosis of low grade non-Hodgkin B-cell lymphomas on cytological material may be problematic and in the past frequently required lymph node excision. We analysed our experience of the value of flow cytometry (FC) as an additional tool for the diagnosis of lymphoproliferative processes in the setting of a university cytology division with a busy fine needle cytology service. METHODS Consecutive cytological specimens with FC over a period of 3 years were retrospectively analysed and correlated with histology and follow-up if available. FC was performed with the following antibodies: CD3, CD4, CD8, CD2, CD7, CD19, CD5, CD10, CD23, lambda and kappa chains. RESULTS Of 299 probes (273 fine needle aspirations and 26 fluids from 285 patients), 179 cases (60%) were diagnosed as reactive, 91 cases (30%) as malignant or suspicious and 29 cases (10%) as inconclusive. The results of histological examination of the lymph nodes were available in 41 of 91 (45%) malignant or suspicious cases and in 13 of 179 (7%) reactive cytological diagnoses. Cytologically diagnosed malignancy was confirmed in all histologically examined cases. In 12 of 13 reactive cytological cases (92%), a benign process was diagnosed histologically. In 34 of 299 cases (11%) additional molecular investigations of B-cell clonality or specific translocations were performed. The lymphomas most frequently diagnosed were follicular lymphoma and lymphocytic lymphoma, followed by mantle cell and marginal zone lymphomas. Correlation with histology showed a sensitivity of 98% and a specificity of 100% for cytology in our series. CONCLUSIONS FC is an important additional tool in the cytological diagnosis of lymphoproliferative disorders. The combined approach has a high diagnostic value that allows a reliable subclassification of low grade B-cell non-Hodgkin lymphomas.