The identification of an epithelial growth factor receptor (EGFR) mutation as a cancer driver gene in nonsmall cell lung cancers, and the development of high-sensitivity mutation test systems have dramatically changed the procedures to treat nonsmall cell lung cancers. Currently, almost all patients with advanced nonsmall cell lung cancer are tested for the presence of EGFR mutation in Japan, and if positive, treating patients with regimens containing EGFR-tyrosine kinase inhibtors (EGFR-TKIs) are considered mandatory. The EGFR mutation test should detect mutant EGFR genes from clinical specimens in which cancer cell content is only 1%. Recently, anaplastic lymphoma kinase fusion genes, rearranged during transfection (RET) fusion genes, and c-ros1 proto-oncogene (ROS1) fusion genes have been reported: all of these genes have drugs that suppress activities and thus can be used for treatment. Genetic tests that are capable of investigating all these mutant genes are required. Moreover, the test system should be equipped with the practical sample isolation procedures, should report the result within a week, should detect mutation from a clinical specimen in which cancer cell content is only 1%, and should be inexpensive and allow all patients with nonsmall cell lung cancer to be tested. The most practical approach constructing such a system is to employ a high-speed sequencer. Systems using them are now being constructed and will soon be introduced to clinical practice.