Cancer risk in patients with monoclonal gammopathy of undetermined significance

To assess the cancer risk of monoclonal gammopathy of undetermined signific ance (MGUS) we identified 1229 cases of MGUS in the period 1978 to 1993. Da ta on cancer occurrence in the MGUS cohort were obtained from the Danish Ca ncer Registry. The expected numbers of cancer cases were calculated from ag e-, sex-, county-, and period-specific cancer incidence rates, In the MGUS cohort 64 new cancers with a known association with M-components were diagn osed versus 5.0 expected giving a standardized incidence ratio (SIR) of 12. 9 (95% confidence interval, 9.9-16.5), The relative risks of developing mul tiple myeloma (SIR 34.3), Waldenstrom's macroglobulinemia (SIR 63.8), and n on-Hodgkin's lymphoma (SIR 5.9) were significantly increased and independen t of time passed from detection of the M-component. The relative risk of ch ronic lymphocytic leukemia was not significantly increased, SIR 2.7 (0.5-7. 7). Among cancer sites without known association with M-components 141 case s were observed versus 94.6 expected giving a SIR of 1.5 (1.3-1.8). This en hanced risk was seen for several non-hematological cancer sites but for mos t cancer sites the risk was dependent on time passed from detection of the M-component, indicating a bias rather than a causal role of MGUS, (C) 2000 Wiley-Liss, Inc.