Correlation between Hematopoietic Stem Cell Engraftment Assay Results and Bone Marrow Biopsy, Flow Cytometry, and Cytogenetics Findings.

Hematopoietic stem cell transplantation following induction chemotherapy is an increasingly successful therapeutic option for patients with leukemia or lymphoma. The use of molecular assays in post-transplant patients has become the standard in evaluating these patients for evidence of engraftment or early recurrence of disease. The detection of residual host cells in the bone marrow (BM) or peripheral blood (PB) following stem cell transplantation often influences subsequent clinical management. The aim of our study is to determine the extent of correlation between the results of PCR-based stem cell engraftment (SCE) assays and BM biopsy (BMBx), multiparameter flow cytometry (FC) and cytogenetics findings in patients who have undergone stem cell transplantation as therapy for hematolymphoid malignancies. We retrospectively reviewed the results of 1103 serial SCE assays performed at The Johns Hopkins Hospital, and 596 of these had temporally corresponding BMBx, FC and/or cytogenetic analysis. Concordance between the results of SCE analysis and those of the latter assays was defined as the detection of similar host/donor compositions. While some cases demonstrated clear discordance between the results, a subset showed an equivocal correlation due to the unclear significance of <5% host DNA by SCE analysis. Of 318 SCE assays with concurrent BMBx, 167(52%) showed concordant results, 104(33%) showed discordant results, and 47(15%) demonstrated an equivocal correlation. Of 221 SCE assays with concurrent FC, 111(50%) showed concordant results, 73(33%) showed discordant results, and 37(17%) demonstrated an equivocal correlation. Additionally, SCE assays were performed on concurrent, paired BM and PB specimens in 168 patients. Concordant results were identified in 141(84%) pairs. Of the remaining 27 pairs, host DNA was detected in the PB of 16 cases in which the BM showed either donor only DNA (6 cases) or <5% host DNA (10 cases). Four cases showed <5% host DNA in the PB and chimeric DNA in the BM. However, donor only DNA was detected in the PB in 7 cases that demonstrated a chimeric BM. Lastly, concurrent SCE analysis and XY FISH analysis was identified in 28 cases. Concordance between these two assays was observed in 24 (86%) cases, whereas one (3%) case was discordant and 3 (11%) cases showed an equivocal correlation. In conclusion, both BMBx and FC show similar but weak correlations to SCE analysis. In contrast, XY FISH analysis demonstrates a strong correlation to SCE analysis. Furthermore, SCE analyses performed on paired PB and BM specimens show an overall good correlation. However, our data suggest that in a subset of cases, SCE analysis performed on PB may detect residual host DNA that is not detectable by SCE analysis of BM, possibly due to the heterogeneity of the marrow composition.