For example, quantitative proteomics has been applied to characterize drug response and detect potential therapeutic escape mechanisms in melanoma cell lines treated with novel inhibitors to heat shock protein 90 (HSP90) and mitogen-activated protein kinase kinase (MEK).69 Clinically, a multivariate serum protein test that assesses the intensity of eight serum mass spectra regions has been developed that can stratify patients according to whether they are likely to have a good or poor outcome with epidermal growth factor receptor (EGFR) tyrosine-kinase inhibitors, such as erlotinib. The gene discussed is EGFR; the disease is melanoma.