Development of a risk index based on CNAs. The copy-number status of 8 genes/regions was assessed in a cohort of 864 patients treated on ALL97/99 by MLPA using the P335 kit. Patients were classified according to the copy-number status (deleted/not deleted) of all 8 genes/regions. A total of 67 unique combinations were observed (see supplemental Table 2, available on the Blood Web site). Patients with each unique combination were classified into risk groups according to the algorithm shown below (A). For combinations observed in ≥10 patients, a Cox regression model was used to estimate the risk of an event and patients were assigned to risk groups (good-risk [GR], PR, intermediate risk [IR] 1 [INT-1], or IR 2 [INT-2]) based on the magnitude of the hazard ratio (HR) and the size of the P value (p). All combinations observed in <10 patients were assigned to the indeterminate (IND) risk group. The event-free survival (EFS) of the 5 risk groups is shown in the Kaplan-Meier graph (B).