PB2077: COMPARISON OF PLASMA CELL PERCENTAGE BY BONE MARROW ASPIRATE MORPHOLOGY AND CD138-STAINED BONE MARROW BIOPSY IN SMOLDERING MYELOMA TO PREDICT TRANSFORMATION TO SYMPTOMATIC MYELOMA

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: Smoldering myeloma (SM) can progress to symptomatic plasma cell myeloma (PCM) and usually requires a bone marrow (BM) plasma cell percentage (PC%) over 10% for diagnosis. PC quantification on BM examination includes PC% from the bone marrow aspirate (BMA) or the percentage of positive PCs on a CD138-stained bone marrow biopsy (BMB) specimen. It is not known which method of plasma cell enumeration at diagnosis correlates best with risk of progression of SM to PCM. Aims: We aimed to assess the BM PC% based on review of BMA and CD138-stained BMB in SM patients to determine if one method is more predictive of progression to PCM. Methods: Bone marrow examination records over a ten year period of patients diagnosed with smoldering myeloma were retrospectively reviewed. PC% based on BMA and BMB was determined and patients classified into Group 1 [both BMA and BMB PC%>10%] or Group 2 [BMA PC%<10% and BMB PC%>10%]. Patient records were reviewed to determine if patients progressed to PCM. Exclusion criteria included cases where the aspirate was aparticulate or the trephine biopsy sample inadequate or of poor quality. Results: 78 SM patients were included in the analysis. 23 patients had a PC% on both BMA examination and BMB of >=10% (Group 1). 55 patients had a PC% of 10% or greater on CD138-stained BMB but <10% on BMA examination (Group 2). No patients had PCs 10% or over on the aspirate smear alone. 24% of patients (19/78) progressed to PCM during the follow up period. 52% of patients in Group 1 transformed to PCM (12/23) compared to 13% patients in Group 2 (7/55 patients). Rate of progression was 20.5 and 3.9 per 100 person-years in Group 1 and Group 2 respectively. Median time to progression was 26 months in Group 1 and 31 months in Group 2. Median transformation-free survival (TFS) was shorter in Group 1; 45 months in Group 1 and not reached in Group 2 (p<0.0003). Median follow up was 25 months in Group 1 (range 5 – 96) and 29 months in Group 2 (range 4 – 96) Summary/Conclusion: Our findings suggest that BMA-PC% is more predictive of transformation to PCM than BMB-PC% in SM patients. BMB morphological assessment retains significance where BMA sample quality is insufficient for analysis.Figure: Keywords: Plasma cells, Bone marrow biopsy, Multiple myeloma, Myeloma