Focal adhesion kinase as a marker of malignant phenotype in breast and cervical carcinomas.
Integrins mediate cell adhesion to extracellular matrix and stimulate signals involved in cell proliferation, survival, and migration. Focal adhesion kinase (FAK) is considered the central molecule in integrin-mediated signaling. Previously, FAK has been implicated in invasive tumor behavior based on Northern or Western blot (immunoblot) using total tumor tissue homogenates. We used immunohistochemistry to demonstrate FAK expression in benign cervical epithelium, dysplasia, carcinoma in situ (CIS), and invasive cervical squamous cell carcinomas (SCCs), as well as in benign breast tissue, atypical ductal hyperplasia, and ductal carcinoma in situ (DCIS) and invasive carcinomas of the breast. We also used polymerase chain reaction to analyze whether infection with the high-risk human papillomavirus (HPV) subtypes correlated with FAK overexpression in CIS of the cervix. We found minimal FAK expression in benign cervical and breast epithelium and in low-grade squamous dysplasia (CIN I and CIN I-II) of the cervix, and variable FAK expression in CIS lesions of the cervix (10 of 14 cases). Most of the invasive SCCs of the cervix (13 of 16 cases) and DCIS of the breast (6 of 8 cases) were positive for FAK. Surprisingly, all DCIS of the breast were also strongly positive (7 of 7). Only 3 of 13 cases of atypical ductal hyperplasia were focally positive for FAK. Regardless of the intensity of FAK staining, all CIS of the cervix were positive for either HPV 16 or 18. We conclude that FAK overexpression is not restricted to invasive phenotype, but rather appears to be a marker for malignant transformation.