Here, we discuss our novel findings, describing a complex and intriguing action of EPHB6 in controlling the initiation, growth and drug resistance of triple-negative breast cancer (TNBC) tumours that lack the oestrogen receptor (ER), progesterone receptor (PR), do not overexpress the HER2 receptor, and represent the most aggressive breast cancer type [16]. This evidence concerns the gene PGR and breast carcinoma.