As amplification of the MCL1 locus is frequently observed in a range of cancer types we investigated the frequency of elevated MCL1 in breast cancer. 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. a The Cancer Genome Atlas (TCGA) Breast data and METABRIC data (not shown)).