Tumor load i.e. neoplastic plasma cells (NPCs) as % of total PCs (A) & of total bone marrow cells (B) in samples evaluated for minimal residual disease. The NPCs constituted ≤50% of the total PCs in protein electrophoresis (PE) & immunofixation negative samples and >60% of the total PCs in PE+ samples (B). Arrow indicates two cases which were PE- but positive on immunofixation and had relatively low numbers of neoplastic PCs (B) <>