A variety of different kinds of alterations can be detected for a single sample, and each of these alteration types may contribute to a change in the drug response; for example, T790M point mutation in EGFR can lead to the resistance of first- and second-generation EGFR-TKIs in NSCLC cancer patients, BCR-ABL fusion is a predictive effect of imatinib in both acute lymphocytic leukemia and chronic myeloid leukemia patients, and MLH1 methylation is associated with resistance to treatment with oxaliplatin in patients with stomach cancer [23]. This evidence concerns the gene MLH1 and gastric cancer.