Minimal residual disease detection provides critical prognostic predictor of treatment outcome and is the standard of care for B lymphoblastic leukemia. Flow cytometry–based minimal residual disease detection is the most common test modality and has high sensitivity (0.01%) and a rapid turnaround time (24 hours). This article details the leukemia associated immunophenotype analysis approach for flow cytometry–based minimal residual disease detection used at St. Jude Children’s Research Hospital and importance of using guide gates and back-gating.
Minimal residual disease detection provides critical prognostic predictor of treatment outcome and is the standard of care for B lymphoblastic leukemia.
Flow cytometry–based minimal residual disease detection is the most common test modality and has high sensitivity (0.01%) and rapid turnaround time (24 hours).
Flow cytometry–based minimal residual disease detection is complicated by variabilities on the antigens examined, combination of antibodies, criteria for the blast numerator, criteria for the cells that defines the denominator, and the approach to flow cytometry data analysis.
Despite these differences, the final minimal residual disease values show similar clinical outcomes.
Leukemia-associated immunophenotype analysis is simplified by guide gates that define normal B-cell populations and is more accurate using back-gating to include all B-lymphoblastic leukemia cells and exclude contaminating events.
Detection of minimal residual disease (MRD) is a critical prognostic predictor and has become the standard of care for B-lymphoblastic leukemia (B-ALL) in response to up front chemotherapy and success in bone marrow (BM) transplantation for relapsed and high-risk ALL. First shown in the pediatric population, similar usefulness has been shown for the adult population. Over time and with the introduction of even more sensitive assays, the threshold for minimal is changing and MRD is being redefined as measurable residual disease.
MRD is often defined as disease below the level of reliable detection by morphology or 5% blasts of the total marrow cellularity. Flow cytometry studies have shown that this 5% value is not very sensitive and values as low at 0.01% residual disease during treatment are predictive of relapse. In addition, high percentages (>5%) of normal precursor B cells or lymphoblasts can be seen in normal or regenerating marrow without residual leukemia, and can complicate disease status determination when using morphology alone or even standard immunophenotyping by flow cytometry. Currently, there is no consensus for the exact MRD percentage for relapse after patient achieve negative MRD. Some institutions use 1% to define relapse, but others such as St. Jude Children’s Research Hospital (SJCRH) still use 5%.