Background: Identification of a novel biomarker of subclinical lymph node metastasis (SLNM) in papillary thyroid microcarcinoma (PTMC) could provide important clues regarding SLNM in PTMC. We evaluated the significance of HGF and c-Met expression in surgically removed tumor tissue from PTMC patients as a predictive marker of SLNM.
Methods: We analyzed the immunohistochemical relationship between HGF and c-Met expression and SLNM in 113 surgically treated PTMC patients with clinically negative nodes presurgery. In addition, we explored whether HGF/c-Met pathway activation enhanced the in vitro migration and invasion of PTC cells.
Results: Positive immunohistochemical HGF and c-Met staining was found in 107 (95 %) and 103 (91 %) cases, respectively. The HGF staining distribution was as follows: no staining in 6 cases, weak staining in 43, moderate staining in 55, and strong staining in 9. Of the nine cases with strong HGF staining, eight (89 %) had SLNM. The c-Met staining distribution was as follows: no staining in 10 cases, weak staining in 39, moderate staining in 59, and strong staining in 5. Of the five cases with strong c-Met staining, three (60 %) had SLNM. The presence of SLNM was strongly correlated with HGF and c-Met expression in PTMC in a univariate analysis (P < 0.05). HGF overexpression was also associated with SLNM in a multivariate analysis (P < 0.05). Stimulation with exogenous HGF and constitutive activation of c-Met enhanced the migration and invasion of PTC cells in vitro by enhancing VEGF-A expression.
Conclusions: HGF/c-Met pathway activation is associated with SLNM of the central neck in PTMC.