Significance of Bone Marrow Plasma Cell Percentage in Patients with Monoclonal Gammopathy of Unknown Significance Developing Multiple Myeloma

Introduction: Monoclonal gammopathies are characterized by the detection of a monoclonal immunoglobulin in the serum or urine and underlying proliferation of a plasma cell/B lymphoid clone. (1) Patients with monoclonal gammopathy of undetermined significance (MGUS) have a clonal plasma cell population in the marrow (<10%) and secrete a monoclonal protein in the serum (<3g/dL) and/or urine. However, they lack clinical features of overt Multiple Myeloma (MM) (lytic bone lesions, anemia, renal impairment and hypercalcemia). In a study from the Mayo Clinic, 59 of 241 patients with MGUS (24%) developed MM over a period of 22 years. (2) The interval from recognition of monoclonal protein to diagnosis of MM ranged from 2-29 years, indicating that patients with MGUS need to be followed indefinitely. Many risk factors have been looked at to identify those with MGUS who are at the highest risk to progress into MM. We hypothesize that a higher number of plasma cells would correlate with a greater risk of progression to MM and sought to find out if this could be documented by arbitrarily dividing patients between < or ≥5% plasma cells seen on initial bone marrow biopsy.

Methods: We retrospectively reviewed patients diagnosed with MGUS at Henry Ford Hospital between 1999-2013 who underwent a bone marrow biopsy for documenting plasma cell percentage. In addition to this, we also recorded serum hemoglobin, calcium, creatinine, monoclonal protein type and amount, serum free light chains, beta-2 microglobulin and urine for monoclonal protein at the time of diagnosis of MGUS as well as last completed values. For patients that had skeletal surveys we noted if lytic lesions were present at diagnosis, as well as cytogenetics and karyotype evaluations on bone marrow biopsy samples, if completed.

Results: 120 patients with bone marrow biopsies were reviewed. Out of this 17 patients were noted from initial bone marrow biopsy to have ≥10% plasma cells. The remaining 103 patients were categorized as having MGUS. While we were not able to complete full statistical analyses, we did note that 14 of these 103 (13.6%) patients went on to develop overt MM. Further evaluation of these patients revealed that 8 of 14 (57%) had bone marrow biopsies showing ≥5% plasma cells. Interestingly the average time to progression into MM in this subgroup was 1,879 days whereas in the 6 of 14 (43%) with bone marrow biopsy showing <5% plasma cells had average time to progression into MM of 1,965 days. Abnormal cytogenetics and karyotypes of the bone marrow biopsy were also seen in 37.5% of the subgroup of patients with ≥5% plasma cells whereas it was only seen in 16.7% of the subgroup of patients with <5% plasma cells. With statistical data analyses we hope to prove significance in the above collected data as well as make further correlations in regards to risk factors in patients with MGUS.

Conclusion: While we have not been able to complete full statistical analyses of the collected data yet, basic review of the above patients with MGUS and ≥5% plasma cells in the bone marrow biopsy showed a trend to develop MM faster by an average of 86 days than those that had <5% plasma cells. These same patients also were more likely to have abnormal cytogenetics and karyotypes of their bone marrow biopsies. There is a need for further investigations to be done in patients with MGUS and higher risk features. It is important that hematologists be able to recognize a high risk MGUS patient as this would lead to closer monitoring and consideration for earlier aggressive treatment to potentially delay progression into overt MM.