Background: Progression of hepatocellular carcinoma (HCC) often leads to vascular invasion and intrahepatic metastasis, which correlate with recurrence after surgical treatment and poor prognosis. HCC may be an unusual cancer affected by continuous inflammation that can lead to consistent upregulation of transforming growth factor-beta (TGF-beta). Chronic inflammation shifts hepatocytic TGF-beta signaling from the tumor-suppressive pSmad3C pathway to the oncogenic pSmad3L pathway. In this study, we investigated the functional roles of Smad3 and its phosphoisoforms in the progression of HCC.
Methods: Tumor tissue microarrays of samples from 272 HCC patients who underwent curative surgical resection were used to detect the expression of Smad3, Smad4, pSmad3C (S423/425), pSmad3L (T179), pSmad3L (S204), and pSmad3L (S213). Disease-specific death was defined as 1) tumor occupying more than 80% of the liver, 2) portal venous tumor thrombus (PVTT) proximal to the second bifurcation, 3) obstructive jaundice due to tumor, 4) distant metastases, or 5) variceal hemorrhage with PVTT proximal to the first bifurcation. At the time of analysis, tumor recurrence was detected in 184 (67.6%) patients, and 96 (35.3%) had died of HCC.
Results: Nuclear and cytoplasmic localization of Smad3, and nuclear localization of Smad4 were observed in 18.0%, 9.9%, and 9.2% of HCCs, respectively. The rates of Smad3 phosphoisoform-immunoreactive HCC varied according to the location of phosphorylation: pSmad3C (S423/425) 8.1%, pSmad3L (T179) 2.6%, pSmad3L (S204) 2.2%, and pSmad3L (S213) 10.3%. Multivariate analyses revealed that pSmad3C (S423/425) (P=0.022) was an independent predictor of longer recurrence-free survival. pSmad3L (S213) (P=0.006), intrahepatic metastasis, multicentric occurrence, and liver cirrhosis were independent predictors of shorter recurrence-free survival. Cytoplasmic Smad3 (P=0.006), larger tumor size, and intrahepatic metastasis were independent predictors of shorter disease-specific survival. Only pSmad3L (S213) did not show an unfavorable influence on recurrence-free survival (P=0.331) on univariate analysis.
Conclusions: pSmad3C (S423/425), pSmad3L (S213), and Smad3 may be predictors of prognosis in HCC patients after curative hepatectomy. pSmad3C (S423/425) and pSmad3L (S213) may be used as immunohistochemical biomarkers to identify patients with a high risk of recurrence.