Effect of CYP2B6*6 on reported AEs. Within each treatment arm, *6 and *1/*1 patients were compared for the reported frequency of 9 specific AEs selected to represent the main toxicities of alkylating agents and purine analogs. Other AEs were grouped together into a tenth category. Collective analysis of all 10 AE categories using the paired Student t test showed a highly significant association between CYP2B6*6 and reduced toxicity after treatment with FC (P = .002). In contrast, no such association was seen in patients treated with Chl or F alone.