Abstract
Introduction/Objective
Myeloma diagnosis by a pathologist requires 10% plasma cells (PC) or a biopsy proven plasmacytoma in addition to myeloma defining events. PC% > 60% is a biomarker of malignancy under this definition. WHO allows for assesment of plasma cell percentage either by aspirate count or by CD138 immunohistochemistry (IHC). There is lack of consensus on aspirate smear adequacy for PC% estimation. Uneven distribution of plasma cells, hemodilution and/or patchy infiltration can lead to gross underestimation. We compared PC% by aspirate count and CD138 IHC and established corelation with serum protein electrophoresis (SPEP) values.
Methods
67 myeloma cases were included after excluding cases with suboptimal or inadequate aspirate smears. Two hematopathologists evaluated the diagnostic marrow (therapy naive) for PC% by aspirate count and CD138 IHC on biopsy/clot section. Corresponding SPEP and Free light chain (FLC) values were obtained. Correlation coefficent was calculated using Pearson correlation coefficient (GraphPad Prism).
Results
The Ig subtypes included IgG (41/67) and IgA (17/67). 12 cases had available FLC values. Both average and median PC% by CD138 IHC was considerably higher (50%, 52%) compared to aspirate count (29%, 21%). However, PC% by aspirate smear count and CD138 IHC demonstrated a significant linear correlation (r=0.71, p60% by CD138 (and not by aspirate count).
Conclusion
CD138 IHC based PC% is consistently higher, nevertheless, statistically significant linear corelation is observed between aspirate count PC% and CD138 IHC. A significant linear correlation is observed between CD138 IHC and SPEP (IgG and IgA), however, no such correlation is observed with aspirate count. More cases were diagnosed as myeloma (11%) and higher propotion of cases (35%) had biomarker of malignancy i.e. PC% >60% by CD138 IHC. Based on these findings, we propose estimation of PC% by CD138 immunostain be a recommended standard practice for better clinicopathologic and biologic correlation.
Plasma Cell Neoplasms in US Solid Organ Transplant Recipients
