IgG and IgA Monoclonal Gammopathies of Undetermined Significance (MGUS) at Low Risk of Evolution: Proposal and Validation of a Prognostic Scoring System

PURPOSE: The presenting clinico-hematologic features of 1283 patients with IgG and IgA class monoclonal gammopathies of undetermined significance (MGUS) were correlated with the frequency of malignant transformation to evaluate the most important variables prognostically associated with its evolution into multiple myeloma (MM).

PATIENTS AND METHODS: Two IgG MGUS patient populations were evaluated: a study sample (553 pts) and a test sample (378 pts). The IgA MGUS population included 352 cases.

RESULTS: Considering IgG cases the median follow-up was 6.7 yrs in the study group vs 3.6 yrs in test group; in the first 47/553 pts developed MM vs 22/378 in the latter. At multivariate analysis serum monoclonal component (MC) £1.5 g/dl, absence of BJ proteinuria, normal serum polyclonal Ig levels and age less than 70 defined a prognostically favourable subset of patients. On the basis of these four variables, pts could be stratified into 3 different 10 yrs-evolution risk groups (HR 1.0, 4.28, 11.6; P<0.001). This scoring system was validated in the test sample. Considering IgA cases, thirty out of 352 patients developed MM after a median follow-up of 4.8 yrs. At multivariate analysis, Hb < 12.5 g/dl and serum polyclonal Ig reduction resulted related with neoplastic progression.

CONCLUSIONS: using simple variables, whose prognostic role we have previously described, we could validate a prognostic model useful to identify situations with different evolution risk in IgG MGUS. Considering IgA cases a possible prognostic role of Hb level emerged, while the negative one of monoclonal component class or serum levels was not confirmed.