Combining with our observation, it indicates CSK, the SRC family kinases negative regulator, functionally linked with PTEN in regulating PI3K signaling in lapatinib resistance, which explained the similar resistance phenotype of CSK and PTEN null GC cells and stable PTEN protein level in CSK null cells in our study (Fig. 2 and Fig. 3e-h). The gene discussed is PIK3CD; the disease is gastric cancer.