Immunoflow cytometry and cell block immunohistochemistry in the FNA diagnosis of lymphoma: a review of 73 consecutive cases.

AIMS To review the results of 73 consecutive fine needle aspirations (FNAs) that were collected by a pathologist and analysed by immunoflow cytometry. Material for a cell block was also collected from some of these lesions. METHODS The setting was a large general hospital in rural New Zealand. The FNAs were performed by a pathologist, or a radiologist for image guided localisations. Material for immunoflow cytometry was collected into RPMI and, when required, material for a cell block was collected into formalin. RESULTS Of the 73 samples collected by FNA nine were inadequate. Light chain restriction could be demonstrated in most FNA samples from B cell lymphomas (28 of 30 adequate samples). The exceptions were two cases of T cell rich B cell lymphoma. Artefactual light chain restriction was seen occasionally in T cell lymphomas, presumably as a result of autoantibodies binding to the cell surfaces. It was possible to subtype most (18 of 30 adequate samples) B cell lymphomas as chronic lymphocytic leukaemia (CLL), follicle centre cell lymphoma (FCCL), or mantle cell lymphoma. The CD4 to CD8 ratio was not usually restricted in T cell lymphomas and coexpression of CD4 and CD8 was not usually found. Loss of pan-T cell antigens was seen in some T cell lymphomas. Four of the six T cell lymphomas and three of the four non-lymphoid malignacies were diagnosed with the aid of cell block immunohistochemistry. Only one of the four cases of Hodgkin's lymphoma showed Reed-Sternberg cells in the FNA smears. CONCLUSIONS It is not always possible to characterise lymphomas as fully with FNA and immunoflow cytometry as is possible with biopsy histology and a full battery of modern investigations. Nevertheless, in the setting of a large rural general hospital immunoflow cytometry on FNA samples is a highly effective method of diagnosing and typing B cell lymphomas. Immunoflow cytometry is of little use for T cell lymphomas or Hodgkin's lymphomas. We advocate the use of cell block immunohistochemistry in preference to immunoflow cytometry for cases in which the cytological appearance of the specimen is overtly malignant but the differential diagnosis includes non-lymphoid malignancy.