Overexpression of c-Met protein in human thyroid tumors correlated with lymph node metastasis and clinicopathologic stage.

To examine the expression of c-Met protein in thyroid tumors and the correlation of c-MET protein expression with lymph node metastasis (LNM) and pathological stage, 111 papillary thyroid carcinomas (PTC), including 44 with synchronous LNM, and 117 follicular adenomas (FA) were immunohistochemically examined using dewaxed sections of formalin-fixed, paraffin-embedded tissues. Immunohistochemical results were confirmed by Western blot analysis. For PTC, positive immunostaining was observed in 107 of 111 (96.4%) cases and was diffusely present in either cytoplasm and nucleus, or only cytoplasm or only nucleus of cancer cells at varying intensities. Staining tended to be stronger in the periphery of cancer cell nests. Positive reaction was also found in 44 of 117 (37.6%) cases of FA. However, the extent and intensity of c-Met immunostaining in FA were far less than those in PTC (p < 0.0001). Forty-four PTC cases (39.6%) exhibited LNM, and the extent and intensity of c-Met expression were significantly correlated with both LNM (p < 0.0001) and pathological stage (p < 0.0001). No significant correlation of c-Met expression with age, sex or tumor size was found. Our findings suggest that PTC expresses c-Met protein much more strongly and intensively than does FA, and that strong and intense overexpression of c-Met protein may be an indicator of the presence of lymph node metastasis and advanced pathological stage of papillary thyroid carcinoma.