Given the potential relevance of MASTL-PP2A/B55 pathway in breast cancer, we first analyzed MASTL expression and the consequences of its depletion in a panel of breast tumor cell lines, including both hormone-positive/luminal (T47D, MCF-7, BT-483, EVSA-T, MDA-MB-415) and triple-negative/basal-like (MDA-MB-231, BT-549, MDA-MB-468, HCC1143) subtypes. This evidence concerns the gene MASTL and breast carcinoma.