Although the use of isogenic cell lines clearly identified APC synthetic lethality with MSC2504877 (Fig. 2A), the varied responses in the panel of CRC tumour cell lines suggested that APC mutation alone might not be a fully penetrant biomarker of single agent tankyrase inhibitor response; we also did not find that the position of truncating mutations in APC correlated with MSC2504877, as has been suggested for other tankyrase inhibitors4. The gene discussed is APC; the disease is colorectal carcinoma.