Development of Myelodysplastic Syndrome and Acute Leukemias in Patients with Monoclonal Gammopathy of Undetermined Significance (MGUS): A Population-Based Study of 17,315 Patients

An increased risk of developing myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) has been observed for over 40 years in patients with multiple myeloma (MM). While treatment for MM has been implicated as the cause of excess MDS/AML, the risk may also be related to the underlying plasma cell proliferative disease process or an inherent predisposition to other hematologic malignancies in patients with plasma cell disorders. A recent study found an increased risk of AML/MDS for patients with monoclonal gammopathy of undetermined significance (MGUS) where there is no confounding chemotherapy effect to consider (Mailankody S, Blood2011; 118:4086-92). However, that report is subject to detection bias (i.e. association is related to reason for electrophoretic testing rather than the result of the test) since the population was not uniformly screened for MGUS. The purpose of this study was to determine if there was an increased risk of AML/MDS and other acute leukemias in persons with MGUS in a large population-based cohort systematically screened for the presence or absence of MGUS.

The study utilized the population-based cohort established to estimate the prevalence of MGUS in the general population (N Engl J Med 2006; 354:1362-9). Serum samples were collected from 21,463 of the 28,038 residents of Olmsted County, Minnesota age 50 years or older as of 1/1/1995. Serum electrophoresis and immunofixation were used to determine MGUS status by testing all serum samples for the presence of a monoclonal protein. MGUS status was then linked to diagnoses entered in the Mayo Clinic Medical Index from 1/1/1975 to last follow up or 5/31/2006. For any patient in whom the diagnosis of AML/MDS or acute lymphoblastic leukemia (ALL) was in doubt, the diagnosis was verified by medical record review. For MGUS patients who progressed to MM or related disorder, only diagnosis of leukemia made prior to progression was considered.

17,315 patients who consented to serum analysis were included in this study; blinded patients included in the original cohort could not be evaluated. The final study cohort represents 435,021 person-years of follow-up. Mean follow up for patients with MGUS (n=605) was 24.64 years (range 0.11–30.57); controls (n=16,710) had a mean follow up of 25.14 years (range 0.01–31.40). MGUS patients had a significantly higher risk of developing acute leukemia (AML/ALL) or MDS compared to controls, risk ratio 2.20 (95% CI 1.23–3.92), p=0.008 (see Table). There was a higher risk of developing AML/MDS compared to controls, risk ratio 1.80 (95% CI .09-3.59), p=0.09. The risk of developing MDS was statistically significant (RR=2.10, p=0.049). MGUS patients had a 4.18-fold increased risk of developing ALL (p=0.010) and a 2.35-fold increased risk of developing any acute leukemia (p=0.050) over the general population. In subset analysis, patients with IgA/IgG MGUS had a 1.99-fold increased risk of developing MDS (p=0.108), while patients with an IgM M spike had a 2.81-fold increased risk of developing MDS over controls (p=0.152). Though MDS was observed in patients with IgA, IgG, and IgM M-spikes, AML was only observed only in patients with IgA or IgG isotypes (n=2/484).

Our population-based study suggests MGUS is associated with a 1.8-fold increased risk of developing MDS/AML over the general population. The risk of AML/MDS is more modest than the 8-fold increased risk suggested in a previous report (Mailankody S, Blood2011; 118:4086-92). The smaller risk ratios in our study are likely related to our population-based cohort design that uniformly screened for the presence or absence of MGUS, and thereby minimized any amplification of risk that can occur in the presence of ascertainment bias. We also found a significant increase in the risk of ALL in persons with MGUS that requires further study. Our study supports the hypothesis that there may be an inherent increased risk of acute leukemia and MDS in patients with plasma cell disorders that is independent of myeloma therapy.

No relevant conflicts of interest to declare.