Rituximab exposure is influenced by tumor burden and influences response to treatment and survival. (A) Mice without tumor had significantly higher rituximab concentrations than mice with tumor (▼). Mice with low tumor burden (< 0.15 × 10⁶ AU) ( □ ) had significantly higher rituximab concentrations than those with intermediate (from 0.15 × 10⁶ to 3 × 10⁶ AU) (△) or high (> 3 × 10⁶ AU) tumor burden (●) (*P < .05, **P < .01, ***P < .001). (B) Mice in CR (○) had significantly higher rituximab concentrations compared with mice in PR (■) or in PD (△). *P < .05, **P < .01, ***P < .001.