As accumulating evidence showed that the strikingly increased intracellular reactive oxygen species (ROS) caused by detachment from extracellular matrix (ECM) greatly contributed to the anoikis of metastatic cancer cell [18–20], we proceeded to determine the intracellular ROS level of GC cells with ARHGAP15 overexpression or knock-down under monolayer or suspension culture conditions by flow cytometry. The gene discussed is ARHGAP15; the disease is metastatic malignant neoplasm.