Advances in Monitoring and Prognostication for Lymphoma by Flow Cytometry

Flow cytometry (FC) is a well-established method important in the diagnosis and subclassification of lymphoma. In this article, the role of FC in lymphoma prognostication will be explored, and the clinical role for FC minimal/measurable residual disease testing as a monitoring tool for mature lymphoma will be introduced. Potential pitfalls of monitoring for residual/recurrent disease following immunotherapy will be presented. Key points • Flow cytometry (FC) is a well-established diagnostic tool in the workup of lymphoma. • Many prognostic immunophenotypic markers by FC have been explored in chronic lymphocytic leukemia (CLL); fewer exist for other mature lymphomas. • Robust FC minimal/measurable residual disease assays exist for CLL but not for other mature lymphomas. • T-cell receptor β constant region 1 evaluation by FC has the potential benefit for diagnosis and monitoring in T cell lymphomas. • Targeted therapies introduce the potential for loss or downregulation of antigen expression; test interference from therapeutic monoclonal antibodies has been reported. Introduction Lymphomas comprise a heterogeneous group of diseases with variable clinical presentations, pathological features, and prognoses. In lymphoma diagnosis, flow cytometry (FC) can provide a detailed immunophenotypic profile of the lesional material and can provide a surrogate of clonality. Advantages of FC include a rapid turn-around time (within hours) and the ability to provide detailed data on subpopulations of cells. In certain lymphomas that may not have a tissue counterpart, for example, chronic lymphocytic leukemia (CLL), FC may constitute the primary diagnostic method. Minimal/measurable residual disease (MRD) can be defined as persistent disease present posttherapy using methods more sensitive and specific than morphologic evaluation. Sensitivity levels in MRD can reach between 0.01% and 0.001% abnormal cells depending on the method utilized. 1 In FC, the quality of MRD testing is influenced by a number of factors including the amount and quality of the specimen, the staining process (including reagent combinations used), the number of cells evaluated, and the approach to data analysis. 2 Recent advances in lymphoma treatment, namely targeted therapies such as therapeutic monoclonal antibodies and chimeric antigen receptor (CAR) T-cells, have practical implications for clinical FC. This article addresses select concepts in monitoring and prognostication by FC in mature lymphomas, with information presented by lymphoma subtype.