Familial Aggregation of Multiple Myeloma and Its Precursor Monoclonal Gammopathy of Undetermined Significance (MGUS): A Population-Based Study in Sweden.

Background: Evidence from multiply affected families, case-control and population-based registry studies implicate a role for genetic factors in multiple myeloma (MM). The aim of this large population-based familial case-control study was to quantify risks of MM, monoclonal gammopathy of undetermined significance (MGUS), and other lymphoproliferative disorders among first-degree relatives of MM patients.

Methods: We identified 13,963 MM patients diagnosed in Swedish hospitals 1958–2005, with linkable relatives. Using the population-based central Population- and Multigenerational registries, we obtained 54,610 matched controls and first-degree relatives of MM patients (n=37,838) and controls (n=151,068). Relatives of MM patients and controls were linked with hospital-based outpatient registries and the central Swedish Cancer Registry to define occurrence of MGUS and lymphoproliferative malignancies. Measures of familial aggregation were calculated by a marginal survival model using relatives as the cohort.

Results: First-degree relatives of MM patients had a significantly increased risk of developing MM [relative risk (RR)=2.1; (95% confidence interval (CI), 1.6–2.9)] and MGUS [2.1 (1.5–3.1)]. The risk estimates were very similar when we conducted analyses by gender of proband, by type of first-degree relative (parent, sibling, offspring), and by age at MM diagnosis (below/above 65 yrs) for probands. Among relatives of MM patients, we found no excess risk of chronic lymphocytic leukemia, non-Hodgkin lymphoma, Hodgkin lymphoma, or lymphoplasmacytic lymphoma/Waldenström’s macroglobulinemia.

Conclusions: In this large population-based study, we found relatives of MM patients to have a 2-fold excess risk of developing MM and MGUS compared with relatives of controls. Our findings support the theory that there are common, shared susceptibility genes that predispose to MM and MGUS. Better characterization of early genetic lesions mediating monoclonal plasma-cell proliferation, survival, and migration in the bone marrow microenvironment will potentially provide clues to pathogenesis and allow identification of novel molecular targets.