Concordance and discordance in myeloma bone marrow studies.

Abstract

e19508 Background: Multiple myeloma (MM) diagnostic costs, including bone marrow (BM) studies: (flow (F), aspirate (manual differential) (A) and biopsy (Bx)) are increasing. BM studies already have underlying discordance issues that may lead to repetitive studies. Thus, elucidation of characteristics associated with concordant/discordant BM studies in identifying plasma cell percentage (PC%) of ≥10, a key MM diagnostic criteria, arises. Methods: A retrospective chart review (total of152 patients diagnosed with MM and managed at UTMB through 1/2016-1/2018) was completed. 56 subjects met inclusion, PC ≥10% in any BM study, and exclusion criteria. Subjects were grouped into BMA vs BMBx and BMF vs BMBx groups and subdivided into MM subtypes for exploratory review. Two-sample Independent t-test (CI 95%) and descriptive statistics were used for comparison of variables. Two-sided p value ≤ 0.05 was considered significant. Results: Sensitivities in identifying BM PC≥10% were as follows: BMA (66.1%), BMF (39.3%) and BMBx (96.4%) (Gold standard: BMA+BMF+BMBx (100%)). Concordance rates were at 60.7% between BMA and BMBx and 35.7% between BMF and BMBx. Larger BMBx spicule size (mean(cm) = 1.3(1.1-1.48) x 0.27(0.22- 0.31) x 0.21(0.19-0.22), p = 0.037) and higher B2 microglobulin (B2m) levels (mean(mcg/mL) = 11.92 (8.04- 15.79), p = 0.003) were associated with BMA and BMBx concordance in typical/secretory MM types but not in oligo-secretory and non-secretory subtypes of MM, nor is associated with BMF and BMB concordance or discordance. Meanwhile, # of BM acquisition attempts, tool types (hand trochar vs drill) for BM acquisition, LDH and CRP levels had no significant associations with concordance or discordance in any BM study groups. Conclusions: BMF is the least sensitive in identifying PC≥10% likely due to PC damage during flow cytometry, and it may be prudent to just perform BMA with BMBx to save on costs. The associations between larger spicule sizes and higher B2m levels to BMA and BMBx concordance are likely due to an increase in the chance of identifying monoclonal PCs in bigger samples, and greater monoclonal PC tumor burden, respectively, and may have predictability benefits.