The advantage of Flow Cytometry to rapidly screen samples for rare events is illustrated here. In the first example, clonal plasma cells (Kappa chain) were detected in a leukapheresis preparation from a patient with Multiple Myeloma . In this case the cells were simultaneously permeabilised and stained with fluorescent antibodies to a surface antigen, CD 38 and polyclonal light chains. Plasma cells can be characterized by their intense staining with CD38 (PE) and high concentration of intracellular light chains (FITC). In the second example, cytokeratin positive tumor cells were detected in the peripheral blood of a patient with breast cancer. In a fairly rapid test, a small aliquot of whole blood is treated with a permeabilizing agent which also lyses the RBC’s, and is stained with a FITC conjugated antibody to cytokeratins, Cam 5.2. In both cases, 50,000 to 60,000 relevant events are stored as listmode files in order to graphically display and enumerate rare events, less than 0.1% in frequency.

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