EFS of 196 patients classified into SS, IS, and RR groups by sensitivity to four-drug combination. Patients were classified into three categories (SS, IS, and RR) by sensitivity to the combination of four drugs (dexamethasone, prednisolone, asparaginase, and vincristine). SS was defined as sensitive to all four drugs, IS as sensitive to two or three drugs, and RR as sensitive to no drugs or to one drug. Three-year EFS (95% confidence intervals) of SS group (n = 42) was 0.833 (0.690 to 0.976), that of IS (n = 80) was 0.735 (0.608 to 0.863), and that of RR (n = 74) was 0.541 (0.411 to 0.670) (P = .0008).