To our surprise, the dramatic impact of loss or inhibition of MCL-1 in MMTV-PyMT tumours that we observed in vivo was not recapitulated in vitro with acute deletion of MCL-1 in cell lines derived from MMTV-PyMT primary tumours (hereafter referred to as tumour cell lines) (Fig. 4A, B and Supplementary Fig. 4A). The gene discussed is MCL1; the disease is neoplasm.