Analysis of comprehensive, publically available data reveals that MCL1 gene amplification and/or mRNA upregulation in breast cancers is at a frequency of up to 20% across different studies, in contrast to much lower frequency alteration of other pro-apoptotic Bcl-2 relatives (Fig. 1a The Cancer Genome Atlas (TCGA) Breast data25–27 and METABRIC data28 (not shown)). This evidence concerns the gene BCL2 and breast cancer.