a–c, Quantitative RT–PCR was used to determine the expression levels of SLC7A11 in paired normal and cancer tissues from colon (a), kidney (b) and liver (c); average expression levels from normal tissues were normalized to 1 in each type of cancer. Mean ± s.d. from two technical replicates are shown. d, Representative heamotoxylin and eosin (H&E) and immunofluorescence staining of SLC7A11 on frozen sections of paired patient cancer and adjacent normal tissues. Magnifcation, ×20. N, normal tissue; C, cancer tissue. Blue, DAPI; green, anti-ATP1A1; red, anti-SLC7A11. e, DNA sequencing was performed on colon cancer samples and specific mutations were identified. Independent experiments were repeated three times and representative data are shown.