Myeloma. Flow cytometry. Staining pattern of marrow cells with surface staining for CD45 (LCA, leukocyte common antigen) and CD138 (syndecan-1). Upper panel shows the presence of a CD45-/CD138+ population. Gating for this population (R1) with evaluation for cytoplasmic kappa and lambda light chains indicates that plasma cells express monoclonal kappa light chains.