Protein Tyrosine Kinase 7 (PTK7) in Breast Cancer: A Retrospective Analysis of Tumour Expression and Association with Clinical Outcome

Protein tyrosine kinase 7 (PTK7), originally known as colon carcinoma kinase (CCK4), is an evolutionary conserved, catalytically defective transmembrane receptor involved in Wnt signalling. PTK7 has been identified as a potential therapeutic target, and a PTK7 antibody drug conjugate (PF-06647020; cofetuzumab pelidotin) has been investigated in phase I clinical trials for triple-negative breast cancer, ovarian cancer, and non-small cell lung cancer. PTK7 protein expression was evaluated in 1136 early-stage invasive breast tumours by immunohistochemistry. In addition, <i>PTK7</i> mRNA expression in the METABRIC (n = 1980) and the TCGA breast cancer cohorts (n = 1082) was evaluated. Associations between PTK7 expression and clinicopathological criteria and patient outcome were determined. No association between PTK7 protein expression and breast cancer-specific survival was observed; however, <i>PTK7</i> mRNA expression in the METABRIC cohort was associated with breast cancer-specific survival (<i>p</i> < 0.001). PTK7 protein and mRNA expression were associated with breast cancer-specific survival of patients with a poor prognostic Nottingham Prognostic Index (NPI) and a moderate prognostic NPI, respectively. Taken together, these data indicate that PTK7 expression is associated with patient outcome in subgroups of breast cancer patients.