With new clinical trials of APR-246 commencing in multiple tumour streams2, our discovery of SLC7A11 expression as a robust companion biomarker, in addition to mut-p53 status, for APR-246, may facilitate selection and enrichment of patients with mut-p53 tumours who are most likely to respond to APR-246 therapy. The gene discussed is SLC7A11; the disease is neoplasm.