Patterns of hematologic malignancies and solid tumors among 37,838 first-degree relatives of 13,896 patients with multiple myeloma in Sweden

There are emerging data to suggest a role for genetic factors in the pathogenesis of multiple myeloma (MM). Based on small numbers, certain solid tumors have been reported to occur more frequently among blood relatives of patients with MM. Using population-based data, we assessed risks for hematologic malignancies, monoclonal gammopathy of undetermined significance (MGUS), and solid tumors among first-degree relatives of patients with MM. We included 13,896 patients with MM and 54,365 matched controls. Also we identified first-degree relatives of patients with MM (n = 37,838) and controls (n = 151,068). Using a marginal survival model, we estimated relative risks (RRs) and 95% confidence intervals (CIs) for hematologic and solid tumors among family members of patients with MM and controls as measures of familial aggregation. Compared with relatives of controls, relatives of patients with MM had an increased risk of developing MM (RR = 2.1; 95% CI 1.6-2.9), MGUS (2.1; 1.5-3.1), acute lymphoblastic leukemia (ALL) (2.1; 1.0-4.2), any solid tumor (1.1; 1.0-1.1) and bladder cancer (1.3; 1.0-1.5). No significantly increased risk was found for other hematologic or solid malignancies. Our findings support a role for a shared susceptibility (genetic, environmental or both) that predisposes to MM, MGUS, ALL and bladder cancer.