Loss of expression of protein tyrosine kinase 7 in invasive ductal breast cancers.

: Protein tyrosine kinase 7 (PTK7) is a catalytically inactive receptor tyrosine kinase that is involved in development and tumorigenesis. PTK7 expression and its functional roles have been investigated in several human cancers, although controversial results have been obtained. In this study, we investigated the expression of PTK7 protein in invasive ductal breast cancer tissues, and analyzed its relationship with clinicopathologic parameters. Seventy-nine consecutive invasive breast cancer tissues were included in the study, and PTK7 protein was detected in invasive ductal breast cancers and normal breast epithelial cells by immunohistochemistry. Positive staining was noted in all normal breast epithelial cells and differential expression was observed in breast carcinomas. Thirty-eight of 79 samples (48.1%) were negative or stained weakly for PTK7 (-), 19 (24.1%) showed moderate staining (+), and 22 (27.8%) were strongly stained (++). PTK7 expression was negatively associated with tumor grade (P=0.025, r=-0.251), tumor-node-metastasis stage (P=0.004, r=-0.317), lymph node metastasis (P=0.002, r=-0.351), human epidermal growth factor receptor 2 expression (P=0.029, r=-0.245), and Ki67 expression (P=0.004, r=-0.317), and positively associated with estrogen receptor (ER) expression (P=0.037, r=0.235). No significant relationship was found between PTK7 expression and patient age or progesterone receptor (PR) expression. Our data indicated that PTK7 protein was down-regulated in breast cancer cells compared with healthy epithelial cells, and that PTK7 may be a tumor suppressor gene in breast cancer. Future studies should explore the molecular mechanisms underlying the down-regulation and functional roles of PTK7 in breast cancer.