Feasibility of HER2 molecular imaging of gastric cancer (GC) at probed-based confocal laser endomicroscopy (pCLE)

Background: Immunohistochemical staining of endoscopic biopsy is the main method for evaluating HER2-positive advanced/recurrent GC, but taking at least five biopsy specimens is recommended because of its highly heterogeneous expression. pCLE enables in vivo real-time microscopic observation with fluorescein. We aimed to determine the feasibility of molecular imaging of HER2 expression with a FITC-labeled HER2 monoclonal antibody at pCLE.
Methods: Two human gastric cancer cell lines (MKN7; HER2 2+, MKN28; HER2-), one breast cancer cell line (SK-BR-3-Luc; HER2 3+), and biopsy specimens taken from GC and surrounding noncancerous mucosa of patients (n=4) with HER2-positive GC were used in this study. The cultured cell lines or biopsy specimen were incubated with FITC-labeled HER2 antibody. After washing, the cell lines and biopsy specimens were directly observed at pCLE. To validate these findings, fluorescent stereomicroscopic observation and immunohistochemical staining of formalin-fixed tissue were performed.
Results: The cell membrane was stained with strong intensity in SK-BR-3-luc, and moderate intensity in MKN-7. No fluorescence signal was detected in MKN28. Network-like staining was observed on the cell surface of biopsy specimens from HER2-positive GC at pCLE, but not on the noncancerous mucosa. These findings were consistent with fluorescent stereomicroscopic imaging and immunohistochemical staining.
Conclusions: Real-time molecular imaging of HER2 at pCLE is expected to contribute to minimally invasive and highly accurate diagnosis for HER2-positive GC.