Standardizing Clinical Workflow for Assessing Minimal Residual Disease by Flow Cytometry in Multiple Myeloma

Minimal residual disease (MRD) status is an established prognostic biomarker for patients with multiple myeloma. Commonly used MRD testing techniques such as next generation sequencing or next generation flow cytometry can detect as little as one or two multiple myeloma plasma cells in 10⁶ normal bone marrow cells. Early pull of bone marrow aspirates (BMA), necessary to achieve such level of sensitivity, can be difficult to secure in routine clinical practice due to the competing need for early pull samples for clinical response assessment, therefore introducing the risk of analytical interference during MRD testing.

To overcome this challenge, we standardized our workflow for collecting specimens by using a technical first pull after needle repositioning for MRD testing. To capture a comprehensive picture of MRD assay performance and specimen adequacy, we tested for MRD on 556 technical first pull bone marrow aspirates by next generation flow cytometry. Among the specimens, several key multiple myeloma treatment milestones were represented: end of induction therapy, two to three months post-autologous stem cell transplant, early and late stages of maintenance therapy.

By using the technical first pull bone marrow aspirate, we achieved an analytical assay input of 10 million nucleated cells for 97.5% of specimens. Our analytical sensitivity reached 10^-6; (i.e., 10 multiple myeloma plasma cells in 10 × 10⁶ bone marrow cells). Twenty-four percent of specimens were significantly hemodiluted. Low assay input or hemodilution quantifiably lowered the assay sensitivity.

Specimen adequacy is, therefore, an important metric to incorporate into MRD status reporting.