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Imaging, Diagnosis, Prognosis |
Authors' Affiliations: 1 School of Surgery and Pathology, University of Western Australia, Nedlands, Western Australia, Australia and 2 Colorectal Unit, St John of God Hospital, Subiaco, Western Australia, Australia
Requests for reprints: Barry Iacopetta, School of Surgery and Pathology M507, University of Western Australia, 35 Stirling Highway, Nedlands, Western Australia 6009, Australia. Phone: 61-8-9346-2085; E-mail: barry.iacopetta{at}uwa.edu.au.
| Abstract |
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Experimental Design: Pathologic markers, disease-specific survival, and the use of adjuvant chemotherapy were recorded in a retrospective, population-based series of 1,156 stage III colon cancer patients with a median follow-up time of 52 months.
Results: In patients treated by surgery alone (n = 851), markers with significant prognostic value included poor histologic grade, T4 stage, N2 nodal status, vascular invasion, and perforation, but not the presence of TILs. In patients treated with 5-fluorouracil–based chemotherapy (n = 305), TILs were associated with significantly improved survival [hazard ratio (HR), 0.52; 95% confidence interval, 0.30-0.91; P = 0.02] and perforation with a trend for improved survival (HR, 0.67; 95% confidence interval, 0.27-1.05; P = 0.16). Patients with TILs or perforation seemed to gain more survival benefit from chemotherapy (HR, 0.22 and 0.21, respectively) than patients without these features (HR, 0.84 and 0.82, respectively).
Conclusion: The apparent survival advantage from 5-fluorouracil associated with TILs and perforation requires confirmation in prospective studies. Because the presence of TILs reflects an adaptive immune response and perforation is associated with inflammatory response, these results suggest that there may be interactions between the immune system and chemotherapy leading to improved survival of colon cancer patients.
The above studies support the notion that immune surveillance plays a significant role in determining CRC prognosis. CD8+ cells and other activated T lymphocytes might suppress the metastasis rather than the growth of these tumors. High levels of infiltrating memory CD45RO+ cells were shown recently in CRC that showed no signs of early metastatic invasion (8). A follow-up study by the same group found that quantitative analysis of the adaptive immune response (CD3+, CD8+, and CD45RO+) could provide prognostic information that was superior to and independent of the International Union Against Cancer tumor-node-metastasis classification system (9). High densities of adaptive immune cells correlated with a highly favorable prognosis regardless of the extent of tumor invasion through the bowel wall or the involvement of regional lymph nodes.
Robust prognostic markers would be especially useful for the management of stage II CRC due to the uncertainty surrounding the overall benefit of chemotherapy for patients with this stage of disease (10). The ability to identify stage II CRC patients with very good prognosis would allow them to be spared the toxicity and inconvenience of adjuvant treatments. Established tumor markers for poor prognosis are extramural vascular invasion, peritoneal involvement, extent of extramural spread, incomplete resection, and perforation (10). It remains to be determined whether the presence of TILs provides prognostic information that is independent of these established markers in the routine clinical setting. Whether the adaptive immune response has value in the prediction of survival benefit from chemotherapy is also unknown.
In the present study, we investigated the prognostic value of routinely reported clinicopathologic features in a large, population-based series of stage III colon cancer with long patient follow-up and known adjuvant treatment status. In contrast to most of the studies published to date, these features were analyzed separately for patients treated by surgery alone and for those who received 5-fluorouracil (5-FU)-based chemotherapy. This has allowed us to evaluate the prognostic significance of various markers, including TILs and perforation, in the absence of possible confounding effects of chemotherapy on survival.
| Materials and Methods |
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Ethics approval for the project was obtained from the Human Research Ethics Committees of the University of Western Australia, the Confidentiality of Health Information, and the four major hospitals.
Adjuvant chemotherapy and survival information. Procedure codes from the morbidity database of the Data Linkage Unit, Health Department of Western Australia, were used to identify patients who began chemotherapy within 120 days of surgery. The hospital records of each case were individually reviewed and only those patients who completed at least four to six cycles with the Mayo regimen of 5-FU/leucovorin were included in the study (n = 305). Patients who initiated chemotherapy but did not complete at least four cycles were excluded (n = 156) because this was considered to represent subtherapeutic management (11, 12). A total of 851 patients were treated by surgery alone. Mortality data were obtained from the Death Registry of the Health Department of Western Australia. Death reports were reviewed individually and classified as death due to colon cancer or from other causes. At the end of the study period, 159 (12.0%) patients died from unrelated causes and 662 (49.8%) from recurrence of colonic cancer. The perioperative mortality rate defined as death within 30 days of operative resection was 4.7% (n = 63). The mean follow-up time for patients was 52 months (median, 37 months).
Statistical analysis. Survival analysis was conducted using Kaplan-Meier analysis and Cox proportional hazards regression. The log-rank test was used to determine significance for Kaplan-Meier analysis. A Cox proportional hazards regression model was developed for survival in which each variable was adjusted for all others. The prognostic and predictive significance of each clinicopathologic variable was examined by multivariate analysis of patient groups treated by surgery alone or with chemotherapy. Statistical significance was deemed as P < 0.05.
| Results |
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The same variables were evaluated for prognostic significance in patients treated with 5-FU (Table 1). Only N2 remained as a significant marker of worse prognosis. Interestingly, female gender and the presence of TILs were associated with significantly better survival in patients treated with 5-FU. This contrasts with their lack of prognostic value in patients treated by surgery alone. Perforation was associated with worse outcome in patients treated by surgery alone (HR, 1.30) but was prognostic for improved survival in patients treated with 5-FU (HR, 0.67).
Predictive significance for response to chemotherapy. One explanation for the observation that TILs and perforation are associated with improved survival in patients treated with 5-FU but not those treated by surgery alone is because these markers are predictive for response to chemotherapy. To test this possibility, we compared the survival of patient subgroups treated with or without 5-FU in a multivariate analysis (Table 2 ). The survival advantage associated with 5-FU chemotherapy in the overall cohort of stage III colon cancer patients was 24%. The features of older age, female gender, T4 stage, mucinous phenotype, and vascular invasion were each associated with a relatively greater survival benefit from chemotherapy. However, the greatest apparent survival benefit from chemotherapy was observed in patients with TILs (Fig. 1 ) or patients who had a perforation (Fig. 2 ). The HRs associated with the use of chemotherapy in these patients were 0.22 and 0.21, respectively (Table 2). Patients with TILs or perforation showed considerably more survival benefit compared with all other clinical or pathologic subgroups, with the exception of T4 stage (HR, 0.46). However, almost half (28 of 62, 45%) of the patients with T4 stage tumors and who were treated with 5-FU also showed evidence of perforation.
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| Discussion |
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The ability to predict which colon cancer patients will gain a survival benefit from 5-FU–based adjuvant chemotherapy regimens has proven much more difficult than finding reliable and robust prognostic markers. Several candidate molecular predictive markers have been proposed, including TP53 mutation, microsatellite instability, CpG island methylation, and thymidylate synthase expression. To date, however, none of these molecular-based markers has been validated in prospective trials with an appropriately powered study design. Current American Society of Clinical Oncology (14) and European (15) guidelines for the treatment of colon cancer state that there is insufficient evidence to recommend any molecular marker to guide routine clinical practice in the use of 5-FU.
Evaluation of the prognostic significance of pathologic markers in stage III colon cancer patients treated with 5-FU in the present study (Table 1) suggested that TILs and perforation may be predictive factors for good response to 5-FU. Both features were associated with better survival in patients treated by 5-FU (HR, 0.52 and 0.67, respectively) but not in patients treated by surgery alone (HR, 0.98 and 1.30, respectively). These findings show the importance of studying patient cohorts that have the same adjuvant treatment status when evaluating the prognostic significance of pathologic and molecular markers. The most obvious explanation for the above results is that TILs and perforation are predictive factors for response to 5-FU.
To investigate this possibility further, we compared the survival of patients treated with or without chemotherapy (Table 2). In the overall patient cohort, 5-FU reduced the HR by 24% compared with patients treated by surgery alone. This compares with reductions of 27% (16) and 34% (17) reported in previous observational studies of elderly stage III colon cancer patients. For the subgroup of older (>65 years) patients, the improved survival with 5-FU (32%) was comparable with these earlier studies (Table 2). The largest reductions in HR associated with 5-FU were observed for patients with TILs or perforation (Table 2; Figs. 1 and 2). These patients gained
4-fold more survival benefit from 5-FU than patients without TILs or perforation.
The results of this work suggest that TILs and perforation have predictive value for positive response to 5-FU in stage III colon cancer. Although requiring confirmation in prospective studies, it is interesting to note that both of these features involve the immune response. Several previous studies have shown that TILs are associated with better prognosis in CRC (2–9). This was also observed here for stage III colon cancer patients treated with 5-FU but not for those treated by surgery alone (Table 1). We have recently shown that TILs had no prognostic significance in a large cohort of 1,306 stage II colon cancers treated by surgery alone (13). TILs might therefore be predictive for a good response to 5-FU rather than being a marker of a less aggressive phenotype in colon cancer. Unfortunately, none of the earlier studies (2–9) reported separate analyses for the prognostic value of TILs in stage-specific patient cohorts treated by surgery alone or with 5-FU. In agreement with the present results, Prall et al. (7) found that stage III CRC patients with high tumor densities of CD8+ cells showed excellent survival when treated with 5-FU compared with those with low densities. Although these authors did not examine the prognostic value of CD8+ densities in patients treated by surgery alone, they did suggest that CD8+ cell density could serve as a predictive factor for benefit from 5-FU chemotherapy.
One of the major limitations of the present retrospective study was that tumors with TILs were identified from pathology reports. Although a proforma reporting system was used for the majority of the study cohort, significant variation among pathologists might still be expected for the reporting of TILs. Further work is required to determine both the prognostic and predictive values of lymphocyte type, density, and distribution in CRC.
Tumor perforation is often characterized by a systemic inflammatory response culminating in septic shock. In contrast to TILs, perforation has generally been associated with poor outcome in CRC (10, 13, 18). The adjusted HR associated with this feature was estimated to be as high as 2.93 in a study of 39 curatively resected colon cancers diagnosed before the widespread introduction of 5-FU chemotherapy (18). Our group previously reported a HR for perforation of 1.21 in stage II colon cancer treated by surgery alone (13). In the present study, the HR for perforation in stage III colon cancer patients treated by surgery alone was 1.30 (Table 1). An unexpected and novel finding of this study was the excellent survival of 28 patients with perforation who subsequently received 5-FU (Table 1; Fig. 2). Similar to TILs, we propose that perforation may be a predictive marker for good response to 5-FU chemotherapy.
The significance of clinical and subclinical perforations remains to be explored further. All such perforations will expose the tumor cells to a relatively new immune environment in the peritoneal cavity that is primed to react aggressively to any breach in gut integrity (19). This is in stark contrast to the immune mechanisms in the gut that are far more tolerant to the presence of bacteria. The initiation of an intense peritoneal inflammatory response may enhance the immune capacity of the body to respond to malignant cells. Similarly, this priming may improve responsiveness to adjuvant chemotherapy.
We hypothesize that postoperative administration of 5-FU chemotherapy to colon cancer patients with TILs or perforation preferentially activates the immune system against micrometastases compared with patients without these features, thus leading to improved survival. Conventional cytotoxic chemotherapy is a potent activator of antitumor immune responses (20, 21). The effects of chemotherapy in this process are thought to be multifactorial and could include the creation of a wave of dead or dying tumor cells that enters the antigen presentation pathway. Chemotherapy could also create a milieu during the recovery phase, particularly from lymphopenia, in which the immune system is receptive to the breaking of tolerance and thereby allows tumor cells to be recognized and eliminated. Finally, chemotherapy might transiently reduce the number and functional activity of T regulatory cells with suppressive properties. Whatever the underlying mechanism(s), the present results suggest that 5-FU chemotherapy is more effective at destroying micrometastatic tumor deposits in patients with TILs or perforation compared with patients without these features.
The current observations made in a retrospective, population-based cohort require confirmation in independent clinical data sets that include both quantitative and qualitative assessment of TILs. Comparison of the immune status between colon cancer patients with or without TILs and with or without perforation is also warranted, particularly at times before, during, and after the administration of 5-FU chemotherapy. Ultimately, such studies may lead to more effective combinations of chemotherapy and immunotherapy for the treatment of colon cancer.
| Acknowledgments |
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| 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 8/13/07; revised 11/29/07; accepted 12/ 5/07.
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