Tissue stroma consists of a variety of matrix substances such as interstitial collagen, fibronectin, elastin, and glycoaminoglycans and a variety of cell types including inflammatory cells, immune cells, fibroblasts, muscle, and vascular cells (Dvorak, 1986
). Stromal microenvironment in tumour has a crucial role in tumour progression. It provides an interface between malignant cells and host tissues (Bissell and Radisky, 2001
). Cumulative evidence suggests that the balance of host–tumour interdependency could modulate the phenotype of a tumour, and thus influence the outcome of the disease. However, appropriate markers to quantify the stromal reaction have yet to be determined.
Vimentin is ubiquitously expressed by cells of mesenchymal origin including fibroblasts, endothelial cells, smooth muscle cells, leucocytes, and some other cells (Dulbecco et al, 1983
; Mor-Vaknin et al, 2003
). In certain carcinomas such as breast cancer or melanoma, vimentin was upregulated in aggressive phenotypes in a phenomenon known as epithelial–mesenchymal transition (Brabletz et al, 2005
). However, this phenomenon was not observed in CRC. In fact, in CRC, vimentin was specifically expressed in the stroma, but not in the tumour cells (Altmannsberger et al, 1982
; von Bassewitz et al, 1982
; Sordat et al, 2000
). Thus, in this study we attempted to quantitate the expression of vimentin to verify the clinical value of the stromal response in CRC.
We found that vimentin expression in the tumour stroma was useful in identifying CRC patients with a poor prognosis. Increased stromal vimentin expression indicated a dynamic change in the tumour stroma during tumour progression. Previous attempts to evaluate the stromal response were based mostly on histological changes of the fibrous tissue in the stroma, including an evaluation of the relative amount of fibrous tissue or the pattern of stroma (Jass et al, 1986
; Ueno et al, 2004
). Results have been controversial with regard to prognosis. Some suggested a positive correlation, but others have suggested otherwise (Jass et al, 1986
; Halvorsen and Seim, 1989
; Harrison et al, 1994
; Ueno et al, 2004
). Nevertheless, these studies indicated that significant histological changes could be observed in the tumour stroma.
A significant part of the change could be attributed to fibroblastic changes, as suggested by other studies, as fibroblasts are the main cell population in tissue stroma. Our data suggest the possibility that stromal fibroblasts may indeed facilitate tumour progression, possibly invasion, and metastasis, leading to a higher rate of disease recurrence. Fibroblasts, being both activated by cytokines and at the same time producing cytokines or other soluble factors, were reported to modulate various aspects of tumour progression including proliferation or invasion (Vogetseder et al, 1989
; Nakamura et al, 1997
), angiogenesis (Orimo et al, 2001
), or inhibition of cell death (Olumi et al, 1998
). Vimentin expression is reportedly universally found in all types of fibroblasts (Skalli et al, 1989
; Sappino et al, 1990
). In comparing the extent of stromal reaction and vimentin expression in this study, however, our data suggest that fibrous tissue itself may not be sufficient to promote tumour progression. Collaboration with other factors in the stroma, including the cellular compartment consisting of lymphocytes and endothelial cells may be necessary to create a microenvironment favourable for tumour progression.
Other histological changes often observed in the tumour stroma are the appearance of lymphocytes. These infiltrating lymphocytes are known as tumour-infiltrating lymphocytes (TIL). Vimentin expression is also found in this group of cells. Thus, increased vimentin expression could also indicate increased numbers of TIL. Whether this group of cells protects the host against the tumour cells, or prevents a tumour-specific immune response, remains a controversial topic. A gradual increase in TIL was observed during melanoma tumorigenesis (Hussein et al, 2006
). However, increased immune cells in CRC are reportedly associated with better survival (Pages et al, 2005
). If indeed the increased vimentin is caused by this group of cells, our results would advocate that TIL suppress the immune response against the tumour. However, we note that recent studies have indicated that different subsets of TIL might have distinct roles in the tumour microenvironment (Yu and Fu, 2006
As vimentin also stains endothelial cells, increased microvessels in these regions also caused an increase in overall vimentin expression in the stroma. As tumours grow, development of blood vessels becomes necessary to provide needed oxygen and nutrients. In CRC, the correlation between microvessel density and prognosis has been variable, with studies indicating both positive and negative correlations (Neal et al, 2006
). In this series, we showed that although the single factor change of microvessel density did not provide any prognostic significance, the overall evaluation with vimentin had useful prognostic value to differentiate between high-risk and low-risk groups.
Furthermore, we found that the prognostic power of vimentin expression was better than that of lymph node metastasis. These data support the notion of vimentin as a novel tumour stromal prognostic marker in CRC. We also found that the prognostic power of vimentin was independent of lymph node status, as well as the stage of histological differentiation. These results support the proposal that stromal therapy may be a viable approach to CRC. Stromal therapy was proposed to be more flexible and applicable to a wider range of disease stages, as its target is dynamic (Liotta and Kohn, 2001
). In hepatocarcinoma, chemotherapy was demonstrated to be more effective, if therapies against the underlying fibrosis were also employed (Friedman et al, 2000
; Bilimora et al, 2001
). It is also of interest that stromal markers, such as vimentin in this study, may be useful in monitoring stromal therapies. Targeting the tumour as an organ would be more effective than targeting the tumour alone.
Here, we provide clinical evidence of stromal response, as evaluated by vimentin expression, as a prognostic indicator for poor prognosis in CRC patients irrespective of lymph node status. Vimentin staining allows an evaluation of overall stromal changes that include fibroblastic changes, microvessel density, infiltrating lymphocytes, and possibly other stromal changes yet to be identified. We note, however, that although the results presented here may be useful as a biological marker, they might not specifically reflect the biological nature of cancer (Nishio et al, 2001
). Further assessment of other stromal reaction markers should allow a better understanding of more specific interactions between tumour cells and the microenvironment. A larger scale prospective study will be necessary to verify the prognostic significance of this stromal marker.