Six-color FC reveals the presence of both abnormal, λ light chain-restricted PCs, and normal, polytypic PCs. Gating on the PCs brightly positive for CD38 and CD138 (upper middle, black arrow) reveals the presence of 2 distinct PC populations as determined by differential expression of CD45 (lower middle). Selective analysis of the PCs with diminished CD45 expression (lower middle, red arrow) reveals that they have abnormal loss of CD19 expression (upper left, red arrow) and have a monotypic staining pattern for λ cytoplasmic immunoglobulin light chains (lower left, red arrow). In contrast, the PCs with relatively brighter CD45 expression (lower middle, blue arrow) express CD19 (upper right, blue arrow) and show polytypic cytoplasmic immunoglobulin light chain expression (lower right, blue arrows).