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Imaging, Diagnosis, Prognosis |
Authors' Affiliations: 1 Department of Surgery, Gastroenterological Surgery, Graduate School of Medicine and 2 Department of Pathology, School of Allied Health Science, Faculty of Medicine, Osaka University, Osaka, Japan
Requests for reprints: Hirofumi Yamamoto, Department of Surgery, Gastroenterological Surgery, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita-City, Osaka 565-0871, Japan. Phone: 81-6-6879-3251; Fax: 81-6-6879-3259; E-mail: kobunyam{at}surg2.med.osaka-u.ac.jp.
| Abstract |
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Experimental Design: Using computer-assisted image analysis, we quantified myofibroblasts in the cancer-associated stroma of 192 colorectal cancers using
-smooth muscle actin as a marker.
Results: The cancer-associated stroma contained various numbers of myofibroblasts (0.35-19.0%; mean, 5.55 ± 3.85%). Tumors with abundant myofibroblasts were associated with shorter disease-free survival rate (P = 0.001) for stage II and III colorectal cancer. Multivariate analysis indicated that
-smooth muscle actin was a significant prognostic factor comparable with lymph node metastasis and superior to other tumor and stromal components, including histology of the tumor invasive front, peritumoral lymphocytic infiltration, and Crohn's-like lymphoid reaction. Moreover, colorectal cancers with synchronous liver metastasis generally displayed an active desmoplastic reaction, which was retained in the metastatic lesion to a similar extent.
Conclusions: The results suggest that the abundance of myofibroblasts in cancer-associated stroma may be a useful indicator of disease recurrence after curative colorectal cancer surgery.
The desmoplastic reaction is thought to be supported mainly by the activation of host fibroblasts referred to as "myofibroblasts" (57). Myofibroblasts are differentiated host fibroblasts that express
-smooth muscle actin (
-SMA) as cytoplasmic microfilaments, and desmin to a limited extent, whereas quiescence host resident fibroblasts express vimentin as intermediate filament proteins (8). Myofibroblasts produce an extracellular matrix enriched in type III and V collagen, which is considered to be responsible for the hard consistency of many carcinomas (9).
Several fundamental studies on myofibroblasts have been conducted to clarify the role of cancer-associated desmoplastic reactions. Although a few studies showed that myofibroblasts might have a protective role against a subset of tumor cells (10, 11), other experiments suggested that myofibroblasts might have a supportive or facilitating role in tumorigenesis and progression of carcinomas of the prostate, breast, and keratinocytes (1214). Thus, the clinical value of myofibroblasts has been flagged as a potentially important marker with respect to diagnosis, treatment, and prognosis of cancer (15). However, to date, a quantitative study of the value of myofibroblasts has not been undertaken.
To elucidate the clinical and biological relevance of the presence of myofibroblasts in cancer-associated stroma, we quantified myofibroblasts in the tumors from 192 patients with colorectal cancer using computer-assisted image analysis with
-SMA as a marker for myofibroblasts. Comparative analyses with collagen deposits in the cancer-associated stroma suggest a specific role for myofibroblasts in tumor progression. For assessment of the prognostic power of the presence of myofibroblasts, we also evaluated other stromal constituents, host protective immune systems, such as Crohn's-like lymphoid reaction (CLR), peritumoral lymphocytic infiltration (PLI), and the histology of the invasive tumor front, as well as conventional clinical pathologic variables.
| Materials and Methods |
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H&E staining and immunohistochemistry. Tissue sections (4 µm thick) were prepared from formalin-fixed paraffin-embedded blocks and stained with H&E solution. Immunostaining was done using the Vectastain avidin-biotin complex method peroxidase kit (Vector Laboratories, Burlingame, CA) as described previously by our laboratories (17, 18). The dilutions of monoclonal antibodies used were as follows: (a) anti-human
-SMA (clone 1A4; DAKO, Carpinteria, CA), 1:50; (b) antiproliferating cell nuclear antigen (PCNA; PC10; Novocastra, Newcastle upon Tyne, United Kingdom), 1:50. Nonimmunized mouse IgG (Vector Laboratories) was used as a substitute for the primary antibody in negative controls.
Computer-assisted image analysis. After staining for
-SMA in colorectal cancer tissue, the sections were viewed under a microscope equipped with a charge-coupled device color camera (Olympus Corp., Tokyo, Japan). A random selection of five fields each in the shallow, middle, and deep layers of the cancer body (a total of 15 fields per specimen) was assessed for
-SMA expression at high-power magnification. In assessment of deep layers, stroma area facing to the tumor frontier was mainly taken. The
-SMA expression in cancer-associated stroma was quantified as the relative percentage of the
-SMA area to the selected field area with an imaging processor, MacSCOPE software (Mitani Corp., Fukui, Japan), as described previously (19). The muscle layer was avoided for this assessment because muscle fibers exclusively express
-SMA. The
-SMA staining was also done in the tumors and liver metastases of stage IV patients who were eligible for liver metastectomies to compare levels of
-SMA expression in metastatic lesions with that in the tumor.
Collagen staining. Collagen staining was done using a collagen staining kit (Collagen Research Center, Tokyo, Japan) as described previously (18). Briefly, paraffin-embedded tissue sections were prepared in 4-µm thickness, deparaffinized in xylene, and rehydrated. After washing twice with PBS for 10 min each, the slides were incubated for 1 h at room temperature with staining solution A, which specifically reacts with collagen. The slides were then washed thrice with PBS and once with distilled water for 5 min each. The tissue fraction containing collagen is stained red. The quantification of collagen deposits in the cancer-associated stroma was executed by computer-assisted image analysis as well.
Assessment of CLR, PLI, and tumor growth characteristics. The density of the CLR, defined as lymphoid aggregates surrounding the periphery of the invasive carcinoma, was assessed as described previously (20). PLI was regarded as "conspicuous" when lymphocytes were scattered in a distinctive connective tissue mantle or cap at the invasive margin of the growth (21). Tumor growth characteristics were classified as expanding or infiltrating according to Jass et al. (21).
Statistical analysis. Statistical analysis was done using the StatView J-5.0 program (Abacus Concepts, Inc., Berkeley, CA). The Kaplan-Meier method was used to estimate tumor recurrence or death from colorectal cancer, and the log-rank test was used to determine the statistical significance. A Cox proportional hazards model was used to assess the risk ratio under simultaneous contributions from several covariates. Associations between discrete variables were assessed using the
2 test. Mean values were compared using the Student's t test. All data were expressed as the mean ± SD. P values of <0.05 were accepted as statistically significant.
| Results |
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-SMA and the corresponding photo image treated with an imaging processor are shown in Fig. 1B and C, respectively (22). The
-SMA expression was found mostly in myofibroblasts, with a little in vascular pericytes. Tumor cells were negative for staining. When five random fields from the upper, middle, and lower layers of the cancer body were assessed for
-SMA expression (a total of 15 fields was measured), the
-SMA scores in all layers varied widely from 0.35% to 19.0% (mean, 5.55 ± 3.85%; Fig. 2A
). However, overall, no significant difference was found between the averages of the three layers (Fig. 2B). The above evaluation of
-SMA was executed separately by two of the investigators (I.S. and C.Y.N.) with similar results. When the colorectal cancer cases were divided into two groups, a high
-SMA group (n = 66) and a low
-SMA group (n = 126) according to
-SMA expression at a cutoff point at the mean value of 5.55%, the patients with high
-SMA expression had a significantly poorer overall survival rate (P < 0.0001; Fig. 2C). When the colorectal cancers were divided according to the median value (4.36%), which equally divided colorectal cancer cases, a similar significant difference was obtained with regard to overall survival (data not shown). When
-SMA expression was compared with the various clinical and pathologic variables listed in Table 1
, no significant associations were found.
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-SMA for predicting disease recurrence of stage II and III colorectal cancers. We then analyzed 145 stage II and III colorectal cancer cases because these intermediate stages display a relatively variable prognosis, which is in contrast to the generally good or extremely poor prognosis for patients with stage I or IV cancers, respectively. Disease-free survival reflects the nature of cancer more specifically than does overall survival because the latter does not distinguish patients with recurrent disease from those without recurrence (23). Moreover, disease recurrence is a practical concern after curative surgery; therefore, further analyses were done based on disease recurrence. As shown in Fig. 3A
, the patients with stage II and III cancers with high
-SMA expression had a shorter disease-free survival rate (P = 0.0004). The relationship between high
-SMA and shorter disease-free survival was maintained when analyzed separately in stage II (without lymph node metastasis) colorectal cancer alone (P = 0.0009), and marginal insignificance was noted in stage III (with lymph node metastasis) alone (P = 0.058). With regard to histologic grade in stage II and III colorectal cancers, high
-SMA expression was associated with poor prognosis within the categories of well-differentiated or moderately differentiated adenocarcinoma (P = 0.0095 and P < 0.0001, respectively; Fig. 3B).
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-SMA expression, a significant correlation was noted between
-SMA expression and infiltrating type (P = 0.046) but not others (data not shown). We then assessed the relationships between the clinicopathologic characteristics listed in Table 1. An inverse association was found between PLI and lymph node metastasis (P = 0.007). In addition, a strong association was noted between PLI and CLR (P < 0.0001). Associations were also found between infiltrating tumor margin and lymphatic invasion (P = 0.005).
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-SMA expression, multivariate analysis showed that
-SMA expression and lymph node metastasis were retained as independent indicators of disease recurrence. The relative risk of recurrence in the high
-SMA group was 2.6-fold that of the low
-SMA group (P = 0.004), similar to that of lymph node metastasis (2.7-fold; P = 0.005; Table 3
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-SMA score in each colorectal cancer case, ranging widely from 3.08% to 52.7% (mean, 19.7 ± 9.17%). No significant relationship was noted between collagen deposits and
-SMA expression (Fig. 5). In contrast to the clear predictive value of
-SMA for disease recurrence (P = 0.0047), collagen deposits did not exhibit such a feature (Fig. 5C). A clinical and pathologic survey indicated that collagen deposits correlated with deeper invasion (P = 0.013) and high-grade differentiation (P = 0.045) but not with the other variables (data not shown).
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-SMA expression in liver metastasis. To explore whether myofibroblast production could occur through a cancer-stroma interaction, we measured
-SMA levels in the primary colorectal cancers and synchronous liver metastasis from 14 stage IV patients. Hepatocytes did not express
-SMA, whereas liver metastasis produced cancer-associated stroma and expressed
-SMA (Fig. 6A and B
). All the colorectal cancer samples except one expressed rather high levels of
-SMA, and a comparative analysis between each primary tumor and a corresponding metastatic lesion showed that both displayed similar
-SMA values (Fig. 6C).
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| Discussion |
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We found that
-SMA expression was a universal indicator of poor prognosis in the entire series of colorectal cancers, as well as in stage II colorectal cancer alone, and that it identified patients at high-risk for disease recurrence within the categories of well-differentiated or moderately differentiated adenocarcinomas. Taken together, these findings suggest that stromal myofibroblasts may have certain features that facilitate cancer progression irrespective of cancer spread to lymph nodes or tumor differentiation. In 2004, American Society of Clinical Oncology concluded that direct evidence did not support the routine use of adjuvant chemotherapy for patients with stage II colon cancer, although they acknowledged that the relative benefit in stage III disease might serve as an indirect evidence of benefit for stage II disease in considering the use of adjuvant chemotherapy for those patients with high-risk stage II disease (29). In this regard, the ability to predict for disease recurrence in stage II disease is of particular clinical relevance because definitive markers, such as lymph node metastasis in stage III, have not been identified thus far.
The precise mechanism for why myofibroblast could be an independent prognostic factor is not clear at present. However, there is evidence that myofibroblasts modulate various aspect of tumor progression (24). For example, they are activated by cytokines, such as transforming growth factor ß produced by tumor cells, and in turn produce cytokines or growth factors that stimulate tumor cells leading to tumor cell proliferation or tumor invasion (30, 31). In addition, myofibroblasts express various cytokines and growth factors, such as vascular endothelial growth factor and its receptors, suggesting a role in tumor angiogenesis (32). A coculture system also revealed that tumor-derived fibroblasts might inhibit tumor cell death (33). It was also suggested that fibroblasts might produce proteinases, which are implicated in tumor invasion (34). Considered together, these findings suggest that the presence of myofibroblasts reflects an increased malignant behavior of the tumor.
To estimate the relative power of
-SMA as a prognostic factor, we evaluated several stromal and tumor-associated factors reported to be of prognostic value (20, 21). We also assessed host protective immune systems, including PLI and CLR. Notably, PLI and CLR displayed a positive relationship, and PLI was negatively associated with lymph node metastasis. The finding that both PLI and CLR displayed prognostic value in the univariate survival analysis suggested that the host immune system may, at least in part, play a protective role against colorectal cancer. However, the prognostic value of PLI and CLR disappeared in the multivariate analysis. In the multivariate analysis,
-SMA expression and lymph node metastasis were retained as significant prognostic factors. Although lymph node metastasis reflects cancer expansion, and thus serves as a powerful prognostic factor for colorectal cancer (16, 35, 36), our results identified the presence of stromal myofibroblast as a strong independent prognostic factor similar to lymph node metastasis.
The character of an individual cancer is thought to reflect the accumulation of numerous gene alterations. Recent DNA microarray analyses provide a great deal of information revealing "cancer personalities." It is postulated that cancers may produce the optimal microenvironment that favors its survival by evolving the surrounding stroma (4), possibly in large part through paracrine signaling between tumor cells and stromal fibroblasts (37). Our results showing a high concordance of
-SMA scores in pairs of primary tumors and their corresponding liver metastasis (Fig. 6) may support the hypothesis that individual cancers produce their own optimal microenvironment. In the context of a highly significant prognostic factor, myofibroblasts may reflect the malignant personality of cancer cells.
In conclusion, despite the retrospective nature of the study, it is apparent from the results that myofibroblasts may be a useful diagnostic tool in clinical practice and our data warrant a large-scale prospective study to establish the clinical utility of stromal myofibroblasts as prognostic indicators.
| Footnotes |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 9/ 1/06; revised 11/17/06; accepted 12/12/06.
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smooth muscle actin and desmin expression in perisinusoidal cells of normal and diseased human livers. Am J Pathol 1991;138:123342.[Abstract]This article has been cited by other articles:
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