A. Mouse TBP-3868 thyroid cancer cells growing in 3D collagen were treated with JQ1 (1 μM) and co-treated with CGP57380 (CGP, 2 μM) for 72 hours and the effect on cell proliferation was determined using the WST-1 assay. ****, p<0.0001 relative to the combination treatment group. B-D. Mouse 3868 thyroid cancer cells were subcutaneous injected in the flanks of syngeneic B6129SF1/J mice and allowed to form tumors for 1 week. Mice with established tumors were randomized and treated with DMSO, JQ1 (12.5 mg/kg), CGP57380 (25 mg/kg), or the combination of JQ1 (12.5 mg/kg) and CGP57380 (25 mg/kg) daily Mon-Fri for 2 weeks. Tumor growth was assessed daily, and tumor volume calculated and normalized to tumor volume at the start of treatment (B). Tumors were collected at the end of treatment and photographed (C). Mice were weighed daily and the effect of inhibitors on mouse weight at the end of treatment was compared to weight at the start of treatment (D).