Breast tumor kinase (Brk aka protein tyrosine kinase 6 (PTK6); EC 2.7.10.2) belongs to the non-receptor tyrosine kinases, distantly related to the c-Src family kinases, with occurrence in the cytoplasma. Brk is activated downstream of multiple growth factor receptors, including MET, EGF receptor, and ErbB2, and confers aggressive breast cancer phenotypes such as growth factor–induced cell migration, anchorage-independent growth, modulation of EMT markers, metastasis, and resistance to targeted therapies[1]. As Brk is aberrantly expressed in both luminal and triple negative breast cancers (TNBC) subtypes, but is not found in the normal mammary tissue, it is an attractive candidate for selective targeting of invasive breast cancer cells[2].