Biological properties of bone marrow plasma cells influence their recovery in aspirate specimens: impact on classification of plasma cell disorders and potential bias to evaluation of treatment response

Abstract

Methods to estimate bone marrow plasma cells (BMPC) basically include histopathology, cytomorphology, and flow cytometry. The present study compares the outcomes of these methods with special focus on the impact of BMPC-specific characteristics on their recovery by either method. Laboratory reports of diagnostic samples from 238 consecutive patients with suspected or known plasma cell disease were retrospectively analyzed. The median (IQR) proportion of BMPC was 30.0% (15.0–70.0%) by histological review (hBMPC), 7.0% (2.0–16.0%) by smear review (sBMPC), and 3.0% (0.8–10.0%) by flow cytometry (fBMPC). The disparity of results between core biopsy and aspirate smear was enhanced in case of poor quality of the smear, increased BM fiber content, higher grade cell atypia, expression of CD56 (all P < 0.0001), the number of cytogenetic aberrations (P = 0.0002), and abnormalities of the MYC gene (P = 0.0002). Conversely, expression of CD19 and a non-clonal plasma cell phenotype were associated with a lower difference between hBMPC and sBMPC (both P < 0.0001). The disparity between the percentages of sBMPC and fBMPC was associated with the quality of the smear (P = 0.0007) and expression of CD56 (P < 0.0001). Our results suggest that the recovery of BMPC in aspirate specimens not only is a matter of sampling quality but also depends on biological cell properties. Aspiration failure due to malignant type features of BMPC may lead to misclassification of plasma cell disorders and represent a bias for the detection of minimal residual disease after therapy.

Effect of the sequence of pull of bone marrow aspirates on plasma cell quantification in plasma cell proliferative disorders

“…Many studies (Supplement Table 4) have shown similar results where PC recovery on flow cytometry is affected by the quality of specimen, but a proportion of PC recovery has also been attributed to processing and biological properties of the disease 5,6,7,11,19–21 . Our results demonstrate that the recovery of PCs on flow cytometry was significantly reduced with increasing PC% on second pull smear ( p < 0.001) and in NDMM ( p < 0.001) than in FCMI (Table 3).…”

“…BMPC% plays a key role not only in disease classification of MM, but also aids in assessing response to therapy. BMPC% assessed on different samples are known to be different and, hence it is recommended to use higher PC value (wherever available) for assigning diagnosis and assessing treatment response in cases of MM 11 . In our study, we demonstrated that the aspirate sample obtained from two different pulls if used to determine BMPC%, will yield divergent results.…”

“…PC enumeration by conventional morphology on BMA smears is a simple technique with no prior processing requirements (like decalcification in a biopsy) and has a rapid turnaround time. However, PC quantification by conventional morphology is complicated by the procedural haemodilution as well as site aspirated leading to underrepresentation of the PCs on morphology smears 11,15 …”

“…Histopathological examination of bone marrow biopsy seems a more realistic approach as it has the propensity to assess the definite in situ status of the BM along with architectural anomalies. However, the long turnaround time (1–4 days) and subjective variation in enumerating PCs on biopsy are few pitfalls which demands the importance of alternative methods to quantify BMPC% 11,15 . Nonetheless, patchy distribution of plasma cells can result in markedly discrepant counts of PCs between BM aspirate and biopsy.…”

“…The smears were evaluated for cellularity, percentage of erythroid precursor cells, percentage of myeloid precursor cells, presence or absence of megakaryocytes and percentage of mature neutrophils. Based on literature review, BMA smears were considered cellular when cells from all the three lineages were present and neutrophils constituted <30% of total nucleated cells 11,12 . We defined presence of ≥10% erythroid precursor cells, ≥10% myeloid precursor cells, <30% neutrophils and presence of ≥1 megakaryocytes as adequate for the respective lineage.…”