OS probability of the 4 risk groups identified by the additive risk model. Whereas the favorable-risk group (3-year OS, 39.5%) and the high-risk group (3-year OS, 3.3%) are defined solely by cytogenetic aberrations, the intermediate-risk group can be subdivided into good intermediate (≤ 3 adverse risk points; 3-year OS, 30.0%) and adverse intermediate (> 3 adverse risk points; 3-year OS, 10.6%). According to log-rank tests, the differences between survival curves are highly significant (P < .001), except between favorable and good intermediate risk (P = .138).