Familiality of benign and malignant paraproteinemias. A population-based cancer-registry study of multiple myeloma families.

BACKGROUND AND OBJECTIVES The occurrence of two or more cases of multiple myeloma (MM) in the same family has been reported from time to time. The current study is the first population- and cancer-registry-based survey to investigate familiality of premalignant or malignant B-cell proliferation. DESIGN AND METHODS A family registry of 218 multiple myeloma cases was compared with the records of the Icelandic Cancer Registry in order to analyze the pedigrees for the occurrence of families with multiple cases of paraproteinemia and hematologic malignancies. RESULTS The relative risk of developing monoclonal gammopathies of unknown significance (MGUS) was not increased among first-degree relatives of MM patients, but there was a significantly increased risk of developing MM for females separately (RR = 3.23, CI 1.17-7.01) and for males and females combined (RR = 2.33, CI 1.12-4.26). Analysis for all hematologic malignancies showed an increased risk for female relatives of MM patients (RR = 1.95, CI 1.10-3.20). Eight families were identified in which the propositus with MM had > 1 relatives with MGUS and > 1 with another hematologic malignancy, including 4 families with another relative with MM. In three families both myeloid and lymphoid malignancies occurred. INTERPRETATION AND CONCLUSIONS Although inheritance does not appear to be a major risk factor for the development of paraproteinemias a significant risk of developing MM was found for female relatives. The occurrence of multiple cases of benign and malignant paraproteinemias in a few families does suggest a hereditary contribution. Further studies of such families might reveal clues on pathogenesis.