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Hepato-Biliary-Pancreatic Surgery Division, Department of Surgery, Graduate School of Medicine, University of Tokyo, Tokyo 113-0033, Japan
ABSTRACT
This study was designed to test the hypothesis that cyclin D1 overexpression is involved in the multistep process of gallbladder carcinogenesis and can be used to predict poor prognosis for patients with gallbladder carcinoma (GBC). Cyclin D1 expression was examined immunohistochemically in a series of specimens, including 8 normal epithelia, 8 benign adenomyoma lesions, 6 precancerous adenomas, and 37 carcinomas of the gallbladder. Four of the 6 (67%) adenomas and 15 of the 37 (41%) adenocarcinomas demonstrated cyclin D1 overexpression (>5% nuclear staining), whereas all normal epithelia and adenomyoma lesions were negative for cyclin D1. Kaplan-Meier curves showed that cyclin D1 overexpression was significantly related to decreased overall survival (P < 0.05) in patients with GBCs. The Cox proportional hazards model identified cyclin D1 overexpression as an independent prognostic marker for death (P = 0.024; risk ratio, 4.2; 95% confidence interval, 1.214.7). To test whether cyclin D1 overexpression is a critical event in gallbladder neoplasms, cyclin-dependent kinase inhibitor p27Kip1 was introduced to ascertain how cyclin D1 affects clinical outcomes. Subsequently, neoplasms were divided into three groups on the basis of the combination of cyclin D1 expression and p27Kip1 status, which had been determined previously. Group 1 showed no abnormality in either cyclin D1 or p27Kip1 expression. Group 2 showed aberrant expression of one of the two proteins, whereas group 3 showed concurrent abnormalities in both proteins. Results indicated that overall survival was greatest in group 1, followed by a significant decrease in group 2 and a more precipitous decrease in group 3. In conclusion, cyclin D1 overexpression is an early event in gallbladder carcinogenesis and independently predicts decreased survival for patients with GBC.
INTRODUCTION
Multiple genetic or epigenetic changes contribute to the multistep process of human carcinogenesis, and some of these changes help with the monitoring of this multistep process. It is important to understand the carcinogenic process and its corresponding molecular basis for each type of cancer. For gallbladder carcinogenesis, the dysplasia to carcinoma and adenoma to carcinoma conventional progressions have been generally ascertained (1 , 2) . However, the molecular mechanism underlying the development and progression of GBC3 is not fully understood. This is possibly because of the relative rarity of GBC, which accounts for only 3% of gastrointestinal cancers and 0.5% of all human malignancies, limiting the number of tumor samples available for study. GBC is one of the most biologically virulent cancers and is difficult to cure by conventional procedures. Elucidation of its molecular basis may be helpful in developing and identifying prognostic biomarkers.
Escaping from normal cell cycle controls is critical for the various processes of carcinogenesis (3, 4, 5, 6) . Cell cycle regulators more often altered in cancers are those controlling G1-S-phase progression. G1-S transition is controlled through interaction of several types of molecules, including CDKs, their positive regulators, cyclins (cyclins D1, D2, D3, and E), and their negative regulators, CDK inhibitors and retinoblastoma protein. CDK inhibitors fall into two classes on the basis of their sequence homology: (a) the INK family, which includes p16INK4, p15INK4B, p18INK6A, and p19INK6B; and (b) the Cip/Kip family, which includes p21WAF1/Cip1, p27Kip1, and p57Kip2. Among these proteins controlling the G1-S transition, cyclin D1 is one of the most strongly implicated in tumorigenesis. Cyclin D1 exerts its effects on cell cycle progression via two mechanisms: (a) cyclin D1-CDK complexes inactivate retinoblastoma protein by phosphorylation; and (b) these complexes bind and sequester Cip/Kip proteins stoichiometrically (7) . Evidence for the oncogenic potential of cyclin D1 is provided by studies with numerous models, in which elevated expression of cyclin D1 shortens the G1 phase of the cell cycle and enhances malignant transformation (8, 9, 10, 11, 12) .
Cyclin D1 overexpression, either with or without gene amplification, has been shown in a variety of human malignancies, including breast (13, 14, 15, 16, 17, 18) , colon (19) , lung (20) , esophageal (21, 22, 23) , liver (24, 25, 26) , pancreatic (27) , tongue (28) , oral verrucous (29) , pharyngeal (30) , and laryngeal (31) cancers and has been identified as a prognostic biomarker for breast (16) , lung (20) , esophageal (22 , 23) , pancreatic (27) , tongue (28) , pharyngeal (30) , and laryngeal (31) cancers. The role of cyclin D1 in GBC has not been extensively studied. Recently, we showed that cyclin D1 overexpression is significantly associated with poor clinical outcomes for patients with extrahepatic bile duct cancer (32) , another type of biliary tract malignancy. Moreover, cyclin D1 overexpression has been suggested to be an early event in human breast (18) , lung (33) , and colon (34 , 35) carcinogenesis and in mouse skin carcinogenesis (36) . On the basis of this background, we postulated that cyclin D1 overexpression may be involved in the multistep process of gallbladder carcinogenesis and may be useful as a prognostic marker for GBC. To test this hypothesis, we attempted to study cyclin D1 expression using immunohistochemistry in a series of surgically resected specimens, including normal epithelium, benign lesion adenomyoma, adenoma, and adenocarcinoma of gallbladder from patients treated surgically who had been in a postoperative follow-up phase.
MATERIALS AND METHODS
Patients.
Thirty-seven GBC lesions surgically resected from 36 patients (one
patient had two cancers) between January 1990 and April 1999 in
our department were studied. There were 17 males and 19 females, with a
median age of 65 years (age range, 4584 years). The
clinicopathological variables were evaluated following the General
Rules for Surgical and Pathological Studies on Cancer of Biliary Tract
of the Japanese Society of Biliary Surgery (37)
. Cancers
were staged following the TNM system of the International Union against
Cancer (38)
. The clinicopathological features are
described in Table 1
. Surgical procedures
included 23 cholecystectomies (single cholecystectomy or
cholecystectomy with resection of <2 cm depth of the liver bed) and 13
extended operations (resection of adjacent organs in addition to the
gallbladder). Four patients who underwent palliative surgery were
excluded from survival analysis.
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50% of tumor cells
showing nuclear p27Kip1 immunoreactivity). Six surgically resected specimens of gallbladder adenomas were studied. None of the adenomas had foci of carcinoma in situ. Eight specimens of adenomyoma, as well as eight specimens of normal gallbladder epithelia obtained from healthy persons who had undergone cholecystectomy when donating partial livers for transplantation, were also included in this study.
Immunohistochemistry.
Five-µm-thick sections were cut from formalin-fixed paraffin-embedded
tissue blocks and mounted on gelatin-coated glass slides. The sections
were dewaxed in xylene, rehydrated through graded concentrations of
ethanol, and then treated with 0.5% hydrogen peroxide at room
temperature for 30 min to block endogenous peroxidase activity. The
sections were immersed in 10 mM citrate buffer (pH 6.0) and
processed in an autoclave for 10 min at 120°C for antigen retrieval
(32
, 40)
. Anti-cyclin D1 antibody (Clone DCS-6;
NeoMarkers, Union City, CA; dilution, 1:50) was applied, and
incubations were performed overnight at 4°C. Immunohistochemistry was
performed by the avidin-biotin complex technique using the Vectastain
ABC Elite kit (Vector Laboratories, Burlingame, CA) with
3,3'-diaminobenzidine tetrahydrochloride development and hematoxylin
counterstaining. Negative controls were sections stained without the
primary antibody. Nuclear staining was considered to indicate specific
cyclin D1 immunoreactivity.
For each case, one section having the greatest area of tumor and one section containing noncancerous gallbladder epithelium were selected for immunohistochemical staining from the tissue blocks on the basis of observation of H&E-stained sections. The scoring of cyclin D1 immunoreactivity was based on examination of 10 high-power (x400) microscopic fields or total tumor (when tumor was smaller than 10 fields) for each case. According to a widely accepted criterion (17 , 18 , 23 , 26 , 30, 31, 32) , tumors that expressed strong immunoreactivity in >5% of the cells were considered cyclin D1 positive (overexpression). All slides were interpreted independently by two investigators (A-M. H. and X. L.) without knowledge of the patients clinical courses.
Statistical Analysis.
The associations between cyclin D1 expression and clinicopathological
variables were assessed using the
2
test.
Survival curves were plotted using the Kaplan-Meier method and compared
using the log-rank test (41)
. The significance of various
parameters for survival was analyzed by the Cox proportional hazards
model (42)
. P < 0.05 was considered
statistically significant.
RESULTS
Normal gallbladder epithelia from either healthy persons or GBC
patients were consistently negative with regard to cyclin D1 nuclear
immunoreactivity (Fig. 1
A),
demonstrating <1% positive cells. All eight adenomyoma lesions were
also cyclin D1 negative (Fig. 1
B). For seven of these
specimens, the percentage of positive epithelial cells was <1%, and
in the eighth specimen cyclin D1 immunoreactivity was observed in 3%
of the epithelial cells. Four of the six (67%) adenomas showed cyclin
D1 overexpression (>5% positive cells; Fig. 1
C) with the
percentage of positive cells ranging from 8% to 90%.
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The duration of follow-up of the patients ranged from 3101 months
(median follow-up, 28 months). The Kaplan-Meier method and log-rank
test were used to evaluate the effect of cyclin D1 expression on
postoperative survival in 32 patients with GBCs, excluding four
patients who underwent nonradical surgery. The 3-year and 5-year
overall survival rates were 68% and 53% for all of the 32 patients.
The corresponding figures were 80% and 71% for the cyclin D1-negative
group and 50% and 30% for the cyclin D1-positive group, respectively.
Cyclin D1 overexpression significantly predicted reduced overall
survival (Fig. 2
; P <
0.05). Multivariate analysis by the Cox proportional hazards model
identified cyclin D1 overexpression (P = 0.024; risk
ratio, 4.2; 95% confidence interval, 1.214.7), decreased
p27Kip1 expression (P = 0.024;
risk ratio, 4.2; 95% confidence interval, 1.313.7), and TNM stage
III/IV (P = 0.001; risk ratio, 5.9; 95% confidence
interval, 1.523.0) as independent predictors of death. The 3-year and
5-year overall survival rates were 84% and 71% for the patients who
underwent cholecystectomy and 40% and 0% for those treated by
extended operations. There was a significant difference between the
survival curves (P = 0.007, log-rank test); however,
the surgical procedure had no significance as an independent prognostic
factor in the Cox proportional hazards model analysis. The effect of
surgical procedure on survival probably resulted from the influence of
disease stage; indeed, 9 of the 13 patients who underwent extended
operations had stage III or stage IV tumors.
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5% cyclin D1 and
50%
p27Kip1); (b) group 2, altered
expression of one of the two proteins (>5% cyclin D1 and
50%
p27Kip1 or
5% cyclin D1 and <50%
p27Kip1); and (c) group 3, concurrent
abnormalities in both proteins (>5% cyclin D1 and <50%
p27Kip1). Kaplan-Meier curves showed that
overall survival was significantly shorter in group 2
(n = 14) than in group 1 (n = 12) and
was even shorter in group 3 [n = 6; Fig. 3
|
The involvement of cyclin D1 overexpression has been reported previously in a wide range of human cancers. To determine the potential oncogenic role of cyclin D1 in human gallbladder carcinogenesis, we designed the present study to evaluate the levels of cyclin D1 expression in a series of surgically resected specimens including normal epithelia, adenomyoma lesions, precancerous adenomas, and adenocarcinomas of the gallbladder. Cyclin D1 overexpression was frequently observed in adenocarcinomas and even in adenomas, but not in any specimen of normal epithelium or adenomyoma. This strongly suggests that increased cyclin D1 expression is an early event in gallbladder carcinogenesis, probably playing a critical role in the transformation of gallbladder epithelial cells. Recently, cyclin D1 overexpression has also been observed in precursor lesions for other types of cancers, including breast hyperplasia (18) , atypical adenomatous hyperplasia of the lung (33) , and adenomatous polyps of the colon (34 , 35) .
It is interesting to note that, in this study, the frequency of cyclin D1 overexpression was higher in adenomas (67%) than in cancers (41%). There are two possible interpretations for this novel phenomenon: (a) in the process of gallbladder carcinogenesis, cyclin D1 overexpression may only be needed for establishment of the transformed phenotype, and in some cases it may no longer be needed for maintenance of the transformed phenotype once the lesions have become malignant; and (b) the dysplasia to carcinoma sequence, as well as the adenoma to carcinoma progression, and other routes also contribute to the development of GBCs. Overexpression of cyclin D1 may be involved only in the adenoma to carcinoma route of gallbladder carcinogenesis and may not be involved in other pathways.
The most important finding in this study is that accumulation of cyclin
D1 adversely affects clinical outcome and serves as an independent
marker predicting decreased survival for patients with GBC. This is
easy to understand, because cyclin D1 shortens the
G1 phase and accelerates the cell cycle
(8)
. We have recently found that deregulation of
p27Kip1, another key protein in
G1-S transition control, significantly correlates
with poor prognosis for GBC patients (39)
. To ascertain
how cyclin D1 affects clinical outcome, p27Kip1
was introduced into this study. The postoperative survival rate was
greatest in patients with no abnormality in either cyclin D1 or
p27Kip1 expression, followed by a significant
decrease in those with aberrant expression of one of the two proteins,
and was even lower in those with concurrent abnormalities in both
proteins (Fig. 3)
. These data suggest that cyclin D1 overexpression,
together with reduced p27Kip1 expression, affects
the clinical course of GBC.
In conclusion, cyclin D1 overexpression is an early event in gallbladder carcinogenesis and independently predicts poor prognosis for patients with resectable GBC.
FOOTNOTES
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.
1 Supported in part by Grant 12671207 for
scientific research from the Ministry of Education, Science, Sports and
Culture of Japan, by a grant from the Japan-China Medical Association
of Japan, and by a grant from the Fujida Memorial Fund for Medical
Research (a fund within the Japan Society for the Promotion of Science)
of Japan (all to A-M. H.). ![]()
2 To whom requests for reprints should be
addressed, at Hepato-Biliary-Pancreatic Surgery Division, Department of
Surgery, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-0033, Japan. Phone: 81-3-3815-5411, ext. 33321;
Fax: 81-3-5684-3989; E-mail: amhui-tky{at}umin.ac.jp ![]()
3 The abbreviations used are: GBC, gallbladder
carcinoma; CDK, cyclin-dependent kinase; TNM, tumor-node-metastasis. ![]()
Received 5/11/00; revised 7/28/00; accepted 8/22/00.
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