For RNA extraction, PDX tumor tissues were processed and homogenized in 300 mL of QIAzol as described earlier (12 (link)). Illumina TruSeq RNA Sample Preparation v2 Guide was used to construct libraries from 1 μg total RNA. The cDNA library was validated on the Agilent 2100 Bioanalyzer DNA-1000 chip. Sequencing was performed as described previously (12 (link)). The bioinformatics strategy outlined in the Keysar and colleagues was used (12 (link)).