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Molecular Oncology, Markers, Clinical Correlates |
1 Department of Pathology and 2 Biostatistics Unit of Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, Alabama
| ABSTRACT |
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Experimental Design: We evaluated 206 (85 African Americans and 121 Caucasians) archival tissue specimens of first primary CRCs for immunohistochemical expression of p27kip-1, and its prognostic significance was analyzed using univariate Kaplan-Meier and multivariate Cox regression survival methods.
Results: Although, similar proportion of CRCs with decreased p27kip-1 expression was observed in all stages (range, 2636%), the decreased p27kip-1 expression has been shown as a marker of poor prognosis only for patients with stage III tumors both in univariate (log-rank test, P = 0.014) and multivariate (hazard ratio = 3.2, 95% confidence interval = 1.37.7; P = 0.01) survival analyses. The decreased expression of p27kip-1 was associated with a high histologic grade (P = 0.016) in stage II CRCs, and with distal tumors (P = 0.001), tumor invasion (P = 0.044), and with local recurrence (P = 0.008) in stage III CRCs.
Conclusions: No prognostic significance was found for p27kip-1 expression in stages I, II, or IV CRCs, and its prognostic value was not associated with either ethnicity or tumor location. These studies suggest that decreased expression of p27kip-1 is an indicator of poor prognosis and aids in identifying a subset of patients with aggressive forms of stage III CRCs.
| INTRODUCTION |
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Aberrations in the molecular components of cell cycle checkpoints are a common feature of many human malignancies, and several of these molecules are known to have prognostic significance in CRC. Of these, p27kip-1, a cyclin-dependent kinase inhibitor that regulates progression of cells from G1 into S phase in a cell cycle is being increasingly recognized as an important factor for determining the biological behavior of invasive tumors. Decreased expression of p27kip-1 has been correlated with advanced tumor stage and short patient survival in several human cancers, including CRC (9, 10, 11)
. Both biochemical and immunohistochemical evaluation of p27kip-1 expression in human CRCs have shown diverse results in relation to its prognostic value (Table 1)
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In this study, we evaluated a large CRC patient population [total = 206 (85 African Americans and 121 Caucasians)] for phenotypic expression of p27kip-1 to assess its prognostic significance based on tumor stage, anatomical location, and patient ethnicity.
| MATERIALS AND METHODS |
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During our initial process of selection, patients with multiple primaries, with multiple malignancies, or with family or personal histories of cancer were excluded; therefore, our study population consists only patients with sporadic first primary CRCs. We included patients who have undergone surgery alone as a therapeutic intervention, but we excluded patients who received pre- or postsurgical chemo- or radiation therapy in our study to control for treatment bias.
Immunohistochemical Staining.
Paraffin sections (5-µm thickness) of blocks representative of both tumor and benign tissues of each case were mounted on Superfrost/Plus slides (Fisher Scientific, Pittsburgh, PA). The immunohistochemical staining procedure was carried out as described earlier (2, 3, 4)
. Specifically, the tissues were incubated for 1 h at room temperature with monoclonal antibody to p27kip-1 (clone 1B4; Novacostra, Newcastle upon Tyne, United Kingdom) after antigen recovery by microwave boiling in citrate buffer (pH 7.4) for 10 min. The remainder of the staining procedure and the protocol for the antigen retrieval were described in detail elsewhere (2, 3, 4)
. Hematoxylin was used as a counterstain. A multitissue control block with colonic lymph nodes and benign colonic epithelium was used as the positive control.
Assessment of p27kip-1 Staining.
The staining assessment was performed by two authors (U. M. and N. J.) independently but together to ensure consistency in evaluation. The proportion of p27kip-1-expressing cells varied from 0 to 100%, and the intensity of nuclear staining also varied from weak to strong. Therefore, the percentage of cells at each intensity of staining were recorded on a scale of 0 (no staining) to +4 (strongest staining) by two authors independently. If there was a disagreement in their assessment, they resolved before combining the individual scores. The immunostaining scores of the two authors were combined to obtain an average percent positive score as well as staining intensity for each case. Using this method of staining assessment, we evaluated expression of p27kip-1 in benign colonic epithelium away and adjacent to invasive malignant lesion. A cutoff value of immunostaining staining score of
0.7 plus at least 50% of malignant cells immunostaining was used to classify tumors with increased expression (
50% cells positive plus
0.7 staining intensity score) or with decreased expression (<50% positivity or <0.7 intensity score) of p27kip-1 antigen. This cutoff value was the median value of p27kip-1 staining in the benign epithelium (average of away and adjacent to invasive lesion). Staining in lymphocytes and uninvolved colonic epithelium within the tissue sections served as internal positive controls for the expression of p27kip-1.
Statistical Analyses.
The association between p27kip-1 and clinicopathological or biological characteristics was analyzed using the
2 test (20)
. Ps were calculated, and significance was assessed at an
level of 0.05. The median follow-up period of the complete study population of 206 patients was 4.7 years (range, <118 years). The period from the date of resection to the date of death or last contact (if alive) was used for survival analyses. Outcome analyses were based on patients who were alive or had died of CRC as described previously (2, 3, 4, 5, 6)
. Univariate overall survival was obtained using Kaplan-Meier estimates (21)
. The log-rank test was used to compare Kaplan-Meier survival curves based on the status of p27kip-1 expression. Separate multivariate Cox regression models (22)
were built for patients with stages I, II, III, and IV CRCs, and the survival of patients was compared with and without p27kip-1 expression after adjustments for confounding variables. The clinical confounding variables of CRC used in these analyses were pT, pN, and M components of Tumor-Node-Metastasis stage, age, sex, ethnicity, tumor location, tumor size, and differentiation. A stepwise model-building procedure was used to determine the significant factors in predicting survival related to CRC. The interactions between p27kip-1 expression with other significant variables were tested for significance. Hazard ratios and 95% confidence intervals were calculated to identify the risk factors.
| RESULTS |
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20%) in a tumor tissue section p27kip-1 was localized in the cytoplasm. For this study, we considered only distinct nuclear expression of p27kip-1. Increased phenotypic expression of p27kip-1 was detected in 70% (145 of 206) of CRCs (Table 2)
The analysis of correlation between the proportions of CRCs with increased expression of p27kip-1 with different clinicopathological parameters in each tumor stage group was shown in Table 3
. The incidence of CRCs with decreased p27kip-1 expression was 36, 28, 30, and 26% in stages I, II, III, and IV, respectively. There was a significant association between p27kip-1 expression and the degree of histological tumor differentiation in patients with stage II CRCs, which is that its expression was gradually decreased from well to poorly differentiated CRCs (
2, P = 0.016; Table 3
). In stage III patient group, the expression of p27kip-1 was significantly associated with the anatomical location of CRCs, the increased p27kip-1 was observed in CRCs located in the proximal colon (91%), and in the rectum (77%) as compared with the distal colon CRCs (39%;
2, P = 0.001). In this patient group, the extent of expression of p27kip-1 decreased as the extent of invasion of tumor into the bowel increased (pT1 to pT4,
2, P = 0.044). Also in the stage III cases, the decreased expression of p27kip-1 was significantly associated with an increasing incidence of recurrence (
2 P = 0.008) and with clinical outcome; specifically, a higher proportion of patients with increased p27kip-1 expression were alive at the time of last follow-up (
2, P = 0.018; Table 3
).
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Survival Analyses.
Kaplan-Meier univariate survival analysis on the complete patient population (n = 206) demonstrated no significant differences in their overall survival between the patient groups with decreased or increased levels of phenotypic p27kip-1 expression (log rank, P = 0.152; data not shown). Because, this study population has a considerable number of African American patients, we also conducted survival analyses to assess the significance of p27kip-1 expression based on patient race; the analyses of clinical outcome demonstrated that in either of the racial groups, the cumulative survival curves of low and increased levels of p27kip-1 expression did not show statistically significant differences (log rank, P = 0.273 and P = 0.183, for African Americans or Caucasians, respectively; data not shown). Univariate survival analyses based on p27kip-1 expression and on tumor location also did not show significant differences for all three anatomical sites (log rank, P = 0.377, P = 0.248 and P = 0.631, for proximal, distal, and rectal tumors, respectively; data not shown).
We also analyzed the significance of p27kip-1 expression in the complete study population based on the tumor stage and found that patients with tumors exhibiting decreased p27kip-1 expression had significantly shorter overall survival only in the stage III patient-group (log rank, P = 0.014; Fig. 1C
). Similar analyses in stage I, stage II, and stage IV groups did not show statistically significant differences between patients with decreased or increased levels of p27kip-1 expression (Fig. 1A, B, and D)
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| DISCUSSION |
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Several abnormalities in the molecular features of cell cycle checkpoints have been implicated in several human malignancies, including CRC; however, the prognostic values of many of these cell cycle antigens are controversial in CRC. For example, wild-type p53 eliminates genetically unstable cells that enter the cell cycle, and a mutant p53 will allow these cells to progress to a malignant phenotype. The role of p53 in colorectal neoplasia has been well studied; however, its value in predicting the clinical outcome has been controversial. Nevertheless, some recent studies from others and our laboratories evaluated its prognostic value based on tumor location and ethnicity and have demonstrated that nuclear accumulation of p53 is an independent prognostic indicator of patients with proximal tumors (23, 24, 25) , specifically, for Caucasian patients (3 , 7 , 8) . These novel strategies of assessing the predictive value of a molecular marker of colorectal neoplasia would yield valuable information, which will be useful in identifying aggressive phenotypes.
Increased expression of p27kip-1in mammalian cells induces a G1 block of the cell cycle (26 , 27) and high levels of p27kip-1 found in quiescent cells suggest that expression of p27kip-1 also plays a role in maintaining cells in G0 (28 , 29) . As with other Kip proteins, p27kip-1 has a nuclear localization signal in its -COOH terminus. Loss of p27kip-1 expression may result in the development and/or progression of tumors; however, this loss of expression does not appear to result from gene mutation (30, 31, 32) . p27kip-1 is posttranslationally regulated by an ubiquitin-proteasome-dependent degradation pathway, and p27kip-1 also is regulated by cell-cell contacts (33) . p27kip-1 expression can also be regulated by transcriptional mechanism. In CRCs, reduced expression of p27kip-1 in the metachronous metastases compared with the corresponding primary tumor suggests that the down-regulation of p27kip-1 in circulating malignant cells may accentuate the ability of these cells to metastasize to liver (34) . Also, accumulation of p27kip-1 has been implicated in the differentiation of different varieties of cells (35 , 36) . In CRCs, Loda et al. (9) demonstrated that absent or low levels of p27kip-1 are caused by increased protease-mediated degradation rather than from altered gene expression.
Variable levels of p27kip-1 expression have been observed in benign and malignant epithelial components of the colorectum (9)
. The role of this molecular marker in assessing the aggressiveness of CRCs and in predicting the clinical outcome of patients with colorectal neoplasia has been examined by several investigators and the majority of these studies, which are cited in the Medline or PubMed (until the end of July 2003) are listed in Table 1
. This review table clearly indicates discrepancy of prognostic significance of p27kip-1 expression in colorectal neoplasia. Several studies reported that the lack of p27kip-1 expression was associated with short patient survival (9
, 11
, 13
, 14
, 37, 38, 39, 40)
; however, such an association was not found in some other studies (41, 42, 43, 44, 45)
. In some studies, it was suggested that p27kip-1 was an independent predictor of patients specifically with early stage CRCs (stages I and II; Refs. 9
, 13
, 39
), whereas, studies by Tenjo et al. (11)
observed that p27kip-1 expression as an independent prognostic marker for patients with stage III CRCs.
In our study, all patients have received a uniform treatment of surgical resection either with curative or palliative intents and none of them were treated with chemotherapeutic agents such as 5-fluorouracil or with any other neoadjuvant or adjuvant therapies. Adjuvant chemotherapies were not common practices at the beginning of our study in 1981, but use of adjuvant therapy for CRC increased in 1988. Although, the Food and Drug Administration has approved leucovorin for use in combination with 5-fluorouracil to prolong survival in the palliative treatment of patients only with advanced CRC (stage IV) in 1952, the adjuvant treatment in combination with 5-fluorouracil after surgical resection in patients with Dukes Stage C colon cancer was approved only in 1990.3 Therefore, we did not identify many patients who received chemotherapy during our study period and as stated in methods section, we excluded patients who received pre- or postsurgical treatment. Thus, using our study population, we evaluated the prognostic value of p27kip-1 expression without treatment biases. Also, we assessed its prognostic value based on race, the tumor stage, and tumor site.
In this study, similar proportions of CRCs with the decreased levels of p27kip-1 expression were noted in all stages (2636%). Similar to studies by Palmqvist et al. (14) , we also did not see a significant association between p27kip-1 expression and the tumor differentiation; however, when stratified by tumor stage, our study found that in stage II CRCs, the decreased expression of p27kip-1 was associated with poorer histological differentiation. This association, however, did not impact overall survival of patients with stage II CRCs. In stage III CRCs, p27kip-1 expression was significantly correlated with tumor location, i.e., distal tumors exhibited decreased levels of p27kip-1 expression and the extent of p27kip-1 expression decreased as the invasion of tumor into the lower layers of the bowel wall increased (pT1 to pT4). Similar to our findings, Ciaparrone et al. (46) also found a significant correlation between p27kip-1 expression and tumor grade with well and moderately differentiated CRCs expressing higher p27kip-1, whereas the poorly differentiated CRCs had significantly lower p27kip-1 expression. Furthermore, we observed that tumors, which exhibited decreased expression of p27kip-1, had higher incidence of local recurrence in patients with stage III CRCs, and such an association also was reported in prostatic carcinoma (47) .
Our study demonstrated in both univariate and multivariate analyses that the increased expression of p27kip-1 was associated with improved survival of patients with stage III CRCs but not with stages I, II, or IV tumors. These results are in contrast to some of the previously published studies where it was shown that decreased p27kip-1 expression was associated with poor prognosis of patients with stage II tumors (9
, 13)
tumors without nodal involvement (stage I plus II; Ref. 39
). However, similar to our findings, studies by Tenjo et al. (11)
observed that p27kip-1 is an independent prognostic marker for patients with stage III CRCs. Although, the exact reasons for these contradictory results are not known, the admixture of our patient population for race and for the tumor site may be affecting these findings. Also, it is possible that in our study, we used monoclonal antibody clone 1B4 and established rigorous standards of evaluation as well as cutoff values (
50% cells with immunostaining score value
0.7), and only nuclear p27kip-1 expression was considered in staining evaluation. Whereas, studies by Zhang et al. (13)
used a different antibody clone (SX53G8), different cutoff values for categorizing tumors as high expressors of p27kip-1 (>10%), considered only cytoplasmic p27kip-1 staining for survival analyses and suggested that decreased expression of p27kip-1 was associated with poor survival of patients with Dukes B tumors in univariate analysis. Unlike studies of Zhang et al. (13)
and Kobayashi et al. (42)
, ours as well as several other studies (Table 1)
have used nuclear p27kip-1 staining for survival analyses. The higher cutoff values used in our study to categorize CRCs into high and low expressors are similar to other investigators; additionally, we used more rigorous standards of staining evaluation that included two independent observers to reduce individual bias. Besides these technical variations, other confounders of patient survival, including the adjuvant treatment therapies received and racial admixture specifically in studies of the United States, were not clearly described in the majority of earlier studies. Moreover, these contradictory findings also suggest that the future larger studies should consider the tumor stage and the anatomical location of tumor in the colorectum, race, and ethnicity in evaluating the prognostic value of p27kip-1 expression in colorectal neoplasia. This has led us to propose that molecular and demographic features should be added to the staging of colorectal tumors (7
, 8)
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It is well established in the literature that patients with higher tumor stage (stages III and IV) have a poorer prognosis than stage I or II and staging is used in clinical practice for therapeutic decision making. To add to this concept, multivariate survival analyses of our study also noted significant differences in patient outcome based on age (
65 years), tumor differentiation (poor differentiation), and ethnicity (African Americans) even after controlling for pathological stage of the tumor (Table 4)
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In this study, we have shown both in univariate as well as in multivariate analyses that decreased expression of p27kip-1 is a significant predictor of poor clinical outcome of stage III patients who received surgery alone as a treatment regimen. Our findings also suggest that in stage III tumors, p27kip-1 expression will determine local recurrence. Also, these higher stage tumors exhibit underlying molecular heterogeneity that might determine the behavior of selected tumors. In our studies, the prognostic value of p27kip-1 expression was not associated with race or the anatomical location of the tumor. As demonstrated in our prior studies (2, 3, 4, 5, 6, 7, 8) , the use of multiple molecular markers, including p27kip-1 expression, may help in identifying more aggressive tumors and in predicting the clinical outcome, thus, might help clinical oncologists in designing or selecting more aggressive therapies for subgroups of patients with colorectal 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.
Requests for reprints: Upender Manne, Assistant Professor, Department of Pathology, University of Alabama at Birmingham, 565-LHRB, Building 701, 19th Street South, Birmingham, AL, 35294-0007. Phone: (205) 934-4276; Fax: (205) 975-9927; E-mail: manne{at}path.uab.edu
3 Internet address: http://www.fda.gov/cder/cancer/druglistframe.htm. ![]()
Received 8/13/03; revised 11/14/03; accepted 11/21/03.
| REFERENCES |
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This article has been cited by other articles:
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M. S. Lyall, S. R. Dundas, S. Curran, and G. I. Murray Profiling Markers of Prognosis in Colorectal Cancer Clin. Cancer Res., February 15, 2006; 12(4): 1184 - 1191. [Abstract] [Full Text] [PDF] |
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