Inhibition of Syk activity by R788 reduces tumor burden and increases survival in mouse models of NHL. Cohorts of mice were adoptively transferred with primary tumors or tumor cell lines. At the first external sign of tumors, mice were treated with either 80 mg/kg per day of R788 or control vehicle for 7 days. One day after treatment, 3 or more mice were harvested from R788 or control groups to determine tumor burden relative to wild-type mice. Representative plots of tumor burden as assessed by total number of live cells in the lymph nodes of mice are shown for (A) primary Eμ-MYC/BCR^HEL tumors, (B) Eμ-MYC/BCR^HEL/sHEL (TBL-1) tumors, or (C) primary Eμ-MYC tumors (n = 2). The remaining mice were left in the vivarium to determine whether R788 treatment affected survival. Representative plots of tumor survival are shown for (D) primary Eμ-MYC/BCR^HEL tumors, (E) Eμ-MYC/BCR^HEL/sHEL (TBL-1) tumors, or (F) primary Eμ-MYC tumors. No AT and no treatment (○), AT tumor and treatment with control vehicle (□), or AT tumor and treatment with 80 mg/kg per day R788 (▲) are shown (n = 3). P values for vehicle versus R788 are less than .002 for Eμ-MYC/BCR^HEL and Eμ-MYC/BCR^HEL/sHEL tumors.