Drugs known as EGFR inhibitors—like erlotinib (Tarceva) and gefitinib (Iressa)—are used to treat non-small cell lung cancer (NSCLC) with so-called ‘activating mutations’ in the EGFR gene. Unfortunately, drug resistance develops relatively quickly in most patients. Resistance is often due to additional EGFR mutations, so-called ‘resistance mutations,’ such as EGFR T790M. Researcher have developed a new EGFR inhibitor, AZD9291, which targets both activating and resistance mutant forms of EGFR. AZD9291 inhibited the growth of EGFR-mutant NSCLC cell cultures and eradicated lung cancer tumors with either activating or resistance mutations in mice. Because AZD9291 is less active against normal, non-mutant EGFR, it may have fewer side effects than other EGFR inhibitors. Initial tests of AZD9291 in patients have been promising.