In this work, we identified the Ring Finger Protein 40 (RNF40) E3 ligase responsible for histone 2B monoubiquitination at lysine 120 (H2Bub1) as strongly involved in the stem cell properties of normal breast tissue and basal-like BC (BLBC), a BC subtype that largely overlaps with TNBC [13]. This evidence concerns the gene RNF40 and breast cancer.