Depiction of the protein expression (DAB MOD value) of EGFR, pEGFR, pAkt, pERK and ERCC1 for the first and last passages of each PDX (DAB MOD: 3,3′-diaminobenzidine mean optical density). The mean difference and 95% confidence intervals (CI) are presented for the comparisons between the first and last passages of each PDX by biomarker (**P<0.01). Tissue data was used for all biomarkers except ERCC1, where the nuclear fraction was solely utilized (nuclear DAB MOD values).