PTK7 and triple-negative breast carcinoma: Initial studies demonstrated that PTK7 is enriched on tumour-initiating cells in triple-negative breast cancer, ovarian cancer, and non-small cell lung cancer, and a humanised anti-PTK7 monoclonal antibody and auristatin microtubule inhibitor conjugate (PF-06647020; cofetuzumab pelidotin) induces sustained tumour regression in vivo [7].