Author reply

Abstract

We appreciate the comments and recommendations of Dr. Auer and Ms. Luider. Although Ficoll-Paque centrifugation may lead to occasional loss of neoplastic lymphoid cells, erythrocyte lysis also may result in the loss of neoplastic populations. Fc receptor binding is less of a problem with Ficoll-Paque-purified cells. However we also use serum to block Fc receptors. The second, fourth, and fifth paragraphs all speak to potential advantages of three or four color flow cytometry over two color flow cytometry. We agree that five parameter analysis accompanied by three color analysis appears to be more sensitive. However, this method was not the standard of care at the time these specimens were analyzed, and still has not been adopted universally. There were no consensus recommendations before 1997. We believe our published results of the utility of two color flow cytometry for evaluating bone marrow aspirates in non-Hodgkin's lymphoma (NHL) specimens provides useful information for clinicians. Because the incidence of surface immunoglobulin negative low grade lymphomas is very low, difficulties in differentiating neoplastic and nonneoplastic cells are rare. Although the comparison of charges for flow cytometric analysis at a U. S. versus a Canadian institution is interesting, the “true cost” of pathologic and immunophenotypic staging is difficult to assess, particularly when comparing health care systems financed through completely different mechanisms. In the U. S., reimbursement through third-party payers generally is only a fraction of the charges. The charges were included only to point out that this is a relatively expensive test, which in our hands added nothing to routine morphologic examination. Dr. Auer and Ms. Luider's suggestion that “flow cytometric analysis may indeed replace the traditional method of staging NHL patients” is not well supported by our study, nor by the results of Coad et al.,1 who found highly sensitive polymerase chain reaction (PCR) was negative in 43% of pathologically positive cases. As with PCR, the sensitivity of flow cytometry, regardless of the number of colors, will be limited by the failure to aspirate sufficient lymphoma cells. This particularly is true of follicular center cells, which often are embedded in reticulin fibers adjacent to bone trabeculae. To our knowledge, there are no published reports of the 100% sensitivity of flow cytometry for bone marrow staging in NHL, which Dr. Auer and Ms. Luider quote from their laboratory. This is an important issue and we would be interested in the results of a study similar to ours applying three color flow cytometry to bone marrow staging for NHL. Dramatically more sensitive results would provide an impetus for adopting the U. S./Canadian recommendations. Michael J. Naughton M.D.*, Jay L. Hess M.D., Ph.D. , Mary M. Zutter M.D. , Nancy L. Bartlett M.D. , * Division of Medical Oncology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, Lauren V. Ackerman Laboratory of Surgical Pathology, Department of Pathology, Washington University School of Medicine, St. Louis, Missouri, Division of Medical Oncology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri