Methods for evaluating a patient’s disease status have not kept pace with the expanding profile of therapeutic options. Since we cannot measure the diameter of a specific tumor in patients with multiple myeloma, we measure changes in the secreted product of the tumor cells (ie, M protein and/or light chain), which is helpful but imperfect. First, some patients have nonsecretory disease, in which case the M protein and serum free light chain cannot be used to assess their disease. We currently follow patients with nonsecretory disease using positron emission tomography (PET)/computed tomography (CT) and bone marrow biopsy because we have no way to track disease response with the usual multiple myeloma blood and urine protein markers. However, following multiple myeloma with bone marrow is not always useful, and some patients who initially demonstrate strong conventional M-protein and serum free light chain markers lose those markers over time. Additionally, for patients who do have paraprotein, we still face some limitations with our conventional multiple myeloma monitoring. Immunoglobulins have a long serum half-life; therefore, test results may reflect changes that actually occurred several weeks prior to the patient’s presentation, not real-time conditions.

We are now testing B-cell maturation antigen (BCMA), an investigational serum marker that has a quick turnover and may allow for a more current indication of tumor load. It has not yet gained widespread acceptance in the general oncology community, but we hope that it will within the next year or so. The newer markers, including both serum BCMA and the free light chain marker, have much more rapid turnover. Serum BCMA may allow us to dial down therapy in some cases, thereby reducing the side effects of unnecessary treatment in our patients. It may also help to lower the need for PET/CT and bone marrow testing, thereby reducing costs. Nonsecretory disease can be assessed with the measurement of serum BCMA. Routine monitoring also includes testing for blood counts, chemistries and renal function, liver function, albumin, and calcium and electrolytes. These tests are generally performed monthly, but we perform them weekly, at a minimum, after treatment initiation to see how a patient is responding to therapy. We usually see patients with smoldering multiple myeloma every month if they require antiresorptive therapy with pamidronate, zoledronic acid, or denosumab. If not, we generally see patients every 2 to 3 months, with monitoring that includes blood and/or urine paraprotein levels.