A recently completed clinical trial examining the use of genetic testing to direct cancer treatment was able to exceed its enrollment goal of 600 participants in less than 2 years instead of the expected 5 years. Patients were willing to participate even though they had to undergo an additional biopsy, revealing considerable interest in personalized treatment based on genetic tests. The trial confirmed that erlotinib (Tarceva) is highly effective in non-small cell lung cancer (NSCLC) patients with a mutation in the EGFR gene. It also found that NSCLC patients with mutations in the KRAS gene did not benefit from the novel cancer drug selumetinib. In contrast, not enough small cell lung cancer (SCLC) patients had any of the investigated mutations to properly test how they responded to treatments. Such mutations will require trials involving thousands of patients to draw reliable conclusions.