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Molecular Oncology, Markers, Clinical Correlates |
First Department of Surgery, School of Medicine, Kagoshima University, Kagoshima 890-8520, Japan
| ABSTRACT |
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Experimental Design: Immunohistochemistry was used to investigate the expression of Smad4 and TGF-ß1 proteins in 258 patients with squamous cell carcinoma of the esophagus. The relationship between expression of these proteins and clinicopathological factors was analyzed, and the usefulness of Smad4 in disease prognosis was evaluated in relation to TGF-ß1 expression.
Results: Smad4 expression was preserved in 32.2% of tumors, and TGF-ß1 expression was identified in 42.6% of tumors. Patients with preserved expression of Smad4 had a higher rate of early-stage carcinoma (P < 0.01) and fewer lymph node metastases (P < 0.01) than those with reduced Smad4 expression. The expression of TGF-ß1 was not associated with any of the clinicopathological factors. Postoperative survival analysis indicated that patients with a tumor in which Smad4 expression was reduced had worse clinical outcomes than those with preserved expression (P = 0.01). In patients with TGF-ß1-negative tumors, the survival rate was significantly higher in patients with a preserved level of Smad4 expression than in those with reduced Smad4 expression (P = 0.02). However, according to multivariate analysis, Smad4 expression could not be used as an independent prognostic factor.
Conclusions: Although Smad4 expression could not be used as a prognostic factor, its expression reflected tumor progression such as tumor depth and lymph node metastasis.
| INTRODUCTION |
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Smad4 is apparently common to all of the ligand-specific Smad pathways and appears to play a role as a central mediator in TGF superfamily signaling (6 , 7) . Smad4 appears to mediate the actions of other Smad proteins. In vitro and in vivo studies have indicated that a mutation in the Smad4 gene, on chromosome 18q21, plays a significant role in the tumorigenesis and progression of carcinoma of the pancreas, colorectum, stomach, and other solid tumors (8, 9, 10, 11, 12, 13, 14, 15) . Although mutation of the Smad4 gene is a rare event in esophageal carcinoma (16) , any relationship between Smad4 protein expression and clinicopathological features remains unclear.
The overexpression of TGF-ß1 has been reported in tissues from various types of carcinomas (17, 18, 19) . TGF-ß1 expression appears to correlate with clinicopathological findings, especially with the prognosis of cancer patients (20, 21, 22, 23) . However, the role of Smad4 remains unclear in squamous cell carcinoma of the esophagus. The purpose of this study was to elucidate the clinical significance of Smad4 and its correlation with TGF-ß1 expression in esophageal squamous cell carcinoma.
| MATERIALS AND METHODS |
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On the basis of the tumor-node-metastasis (TNM) classification of the International Union against Cancer (24) , 45 of the 258 patients had T1 tumors, 34 patients had T2 tumors, 119 patients had T3 tumors, and 60 patients had T4 tumors. With regard to location, 33 tumors were located in the upper third of the esophagus, 134 tumors were located in the middle third of the esophagus, and 91 tumors were located in the lower third of the esophagus. Pathologically, all of the tumors were squamous cell carcinoma (101 tumors were well differentiated, 113 tumors were moderately differentiated, and 44 tumors were poorly differentiated). Lymph node metastases were present in 165 of 258 patients (64.0%). All of the M1 tumors were attributable to distant lymph node metastases.
Immunohistochemical Staining and Evaluation.
The specimens were cut into 3-µm-thick sections and mounted on glass slides. Immunohistochemical staining was performed using avidin-biotin peroxidase method as described previously (22
, 23
, 25)
. Briefly, after deparaffinizing in xylene and rehydrating in ethanol, the sections were heated in a citrate buffer (0.01 M, pH 6.5) at 120°C for 10 min to reveal the antigen. Next, sections were incubated with either the primary anti-Smad4 monoclonal antibody (1:300; Smad4: B-8; Santa Cruz Biotechnology, Inc., Santa Cruz, CA) or anti-TGF-ß1 antibody (1:100; TGF-ß1: V; Santa Cruz Biotechnology, Inc.) and left overnight at 4°C. The sections were incubated with biotinylated antimouse IgG and avidin-biotin peroxidase (Vector Laboratories, Burlingame, CA) and visualized using diaminobenzidine tetrahydrochloride. In the negative control group, 1% BSA was used in place of the primary antibody.
The expression of Smad4 by malignant cells was compared with that of normal epithelial cells located away from the tumor. Tumor cells that stained as strongly as normal epithelial cells were considered positive (+), whereas those that showed weaker staining patterns than normal epithelial cells or did not stain at all were considered weak (±) or negative (-), respectively. The tumors were then classified based on their Smad4 expression after overview of the section and were considered to have preserved Smad4 expression if >50% of the tumor cells were Smad4 positive. The tumors classified as having reduced expression were those that did not fit into the above categories.
TGF-ß1-positive expression was determined by counting the number of tumor cells in which the cytoplasm was stained with the anti-TGF-ß1 antibody. To evaluate this, 10 fields (within the tumor and at the invasive front) were selected, and expression in 1000 tumor cells (100 cells/field) was evaluated using high power (x200) microscopy. The average labeling index of TGF-ß1 was assessed according to the proportion of positive cells in each field. TGF-ß1 expression was graded as negative (-) if
10% of cancer cells were stained or positive (+) if >10% of cancer cells were stained (21
, 22) .
Statistical Analysis.
A statistical analysis of group differences was performed using
2 and t tests. The Kaplan-Meier method was used for survival analysis and evaluated by the Wilcoxon test. The prognostic factors were examined by univariate and multivariate analyses (proportional hazards regression model). P < 0.05 was considered statistically significant.
| RESULTS |
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Smad4 or TGF-ß1 Expression and Clinicopathological Features.
The number of cells with reduced Smad4 expression increased as the tumors invaded deeper layers (P < 0.01). The percentage of lymph node metastasis was significantly different in patients with preserved Smad4 expression compared with patients with reduced Smad4 expression (P < 0.01). Further analysis revealed that the patients with preserved Smad4 expression had early-stage esophageal carcinoma. The expression of TGF-ß1 was not associated with any of the clinicopathological factors (Table 1)
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| DISCUSSION |
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50% of patients with esophageal squamous cell carcinoma have an abnormality in the TGF-ß1 protein level, irrespective of the stage of tumor progression. The present study indicates that the 5-year survival rate is significantly higher in patients with preserved Smad4 expression than in those with reduced Smad4 expression because patients with preserved expression belong to a group of patients with relatively early-stage carcinoma. To better understand the role of Smad4 and its relationship to the TGF-ß1 superfamily, we also studied TGF-ß1 expression. Our results suggest that the 5-year survival rate does not differ significantly according to TGF-ß1 expression between patients whose tumors express TGF-ß1 and patients whose tumors do not express TGF-ß1. Several studies suggest that there is a relationship between TGF-ß1 expression and the prognosis of patients with various types of carcinomas (20, 21, 22, 23 , 26) . However, few reports have been published on the relationship between TGF-ß1 expression and prognosis of patients with esophageal squamous cell carcinoma. The results obtained from our study suggest that there is a relationship between TGF-ß1 expression and tumor carcinogenesis, but not tumor progression, in esophageal squamous cell carcinoma.
Because TGF-ß1 acts as a cell cycle inhibitor, which has a biphasic effect on tumor growth, some factor in turn must influence TGF-ß1 activity. In the present study, we therefore analyzed the presence of both TGF-ß1 and Smad4 in tumor cells. The results indicate that patients with TGF-ß1-negative tumors have significantly higher postoperative survival rates when Smad4 expression is preserved. This reflects both the effects of TGF-ß1 on carcinogenesis of esophageal squamous cell carcinoma and the relationship between TGF-ß1 and its signaling transducer, Smad4. The correlation between TGF-ß1 and Smad4 has an influence on the prognosis of esophageal cancer patients. However, multivariate analysis suggests that Smad4 expression is not an independent prognostic factor but is closely related to tumor depth or lymph node metastasis.
In conclusion, Smad4 expression is related to the stage of tumor progression such as depth of invasion and lymph node metastasis. Although Smad4 is not an independent prognostic factor, the examination of Smad4 expression, especially its relationship to the TGF-ß superfamily signaling pathway, is useful for gaining a better understanding of the malignant property of esophageal squamous cell carcinoma.
| FOOTNOTES |
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1 Supported in part by a Grant-in-Aid for scientific and cancer research from the Ministry of Education, Science and Culture of Japan. ![]()
2 To whom requests for reprints should be addressed, at First Department of Surgery, School of Medicine, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan. Phone: 81-99-275-5361; Fax: 81-99-265-7426; E-mail: natsugoe{at}m2.kufm.kagoshima-u.ac.jp ![]()
3 The abbreviation used is: TGF, transforming growth factor. ![]()
Received 11/28/01; revised 2/12/02; accepted 2/20/02.
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