Approximately 70% of patients with unresectable non-small cell lung cancer (NSCLC) who receive and progress through frontline chemotherapy will be eligible for second line treatments. Any of the agents which are available for frontline therapy can be used in the salvage setting, though only erlotinib, docetaxel, and pemetrexed (in non-squamous cell carcinoma) are FDA-approved in the salvage setting based upon their demonstrated survival benefit in randomized phase III trials. All three appear to be roughly equivalent in terms of clinical benefit, which is admittedly modest, with response rates <10%, clinical benefit rates of approximately 50%, and overall survivals of approximately 6 months. Still, a substantial number of patients may not benefit from the agents in the salvage treatment setting, thus it is critical to identify those patients who stand to benefit the most.