The role of thymidylate synthase (TS) is essential as a key rate-limiting enzyme in DNA synthesis. It is the primary target of fluorouracil and its derivates in colorectal cancer. In this study, TS mRNA expression was examined in primary tumor and normal tissues from 76 patients with high- risk stage II/III colorectal cancer by laser capture microdissection and polymerase chain reaction. Thirty (39.47%) patients were found to have higher TS expression in primary tumors with earlier stage (P = 0.018), lower histological grades (P = 0.001) and high frequency microsatellite instability (P = 0.000). Multivariate analysis showed that microsatellite instability, histological grade and number of lymph nodes examined are independent prognostic markers.
The online version of this article (doi:10.1186/1756-8722-4-33) contains supplementary material, which is available to authorized users.
Yanyan Liu, Qingxin Xia, Yanzhao Jia contributed equally to this work.
Authors' contributions
YL and SY designed the study, interpreted data; YL wrote the manuscript; QX and BW reviewed diagnoses of pathology; YJ performed the experiment; HG performed the statistical analysis; YH collected patient data and samples.
All authors have read and approved the final manuscript.
Abkürzungen
CRC
Colorectal cancer
TS
thymidylate synthase
LCM
Laser capture microdissection
MSI
Microsatellite instability.
To the editor
Adjuvant chemotherapy can prolong survival of patients with high-risk, stage II/III colorectal cancer (CRC) after curative surgical resection [1‐3]. Thymidylate synthase (TS) plays a major role as a key rate-limiting enzyme in DNA synthesis and serves as the primary target of fluorouracil and its derivates in CRC. It appears to have predictive and prognostic values [4, 5]. Although the differences in TS expression among primary tumors, lymph nodes and other metastases have been reported [6], the pattern of TS expression in normal and tumor tissues has not been well characterized.
In this study, Laser capture microdissection (LCM) combined with polymerase chain reaction was used to examine TS gene expression in 76 patients with high risk II/III stage CRC (Table 1). Microsatellite instability (MSI, a panel of five loci recommended by National Cancer Institute) and clinicopathological features were analyzed at the same time.
Table 1
Clinicopathological Features
Features
Value
Number
76
Median age, year
58 (30-65)
Male sex, %
55.26
Histological grades (%)
Low (G1 and G2)
75.00
High (G3 and G4)
25.00
Tumor Site(%)
46.8
Colon
27.63
Rectum
72.37
Staging (%)
High-risk II
65.79
III
34.21
Number of lymph node involved (%)
0
64.47
1-3
25.00
More than 3
11.00
Median number of lymph node examined
11 (6-38)
Adjuvant regimen (%)
5-fluorouracil/leucovorin
86.84
5-fluorouracil/leucovorin/oxaliplatin
13.16
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There were 32 (42.11%) patients with differential expression of TS gene between normal mucosa and primary tumor cells. Thirty of them (39.49%) have showed higher level of TS in primary tumors than in normal tissues.
To study the significance of the differential expression of TS in primary tumors, clinicopathological features, including age, gender, stage, histological grade, tumor site, and the number of lymph nodes examined, were analyzed and compared. The results showed that higher TS gene expression in primary tumors correlated to earlier stage (stage II, P = 0.018), and lower histological grades (G1 and G2, P = 0.001), but not to the other parameters defined above.
MSI was also examined in these patients. High frequency of MSI was found in 32.89% (25/76) of the patients in this study. The frequency of MSI was found to be significantly higher in patients with higher TS gene expression than those with lower TS expression (76.67% versus 4.35%, P = 0.000).
When the median time of relapse-free (RFS) and overall survival (OS) was compared, there was significant improvement of RFS (62.80 vs 40.67 months, p = 0.030) and OS (66.80 vs 51.67 months, p = 0.029) in patients with higher TS expression (Figure 1). Multivariate analysis was performed using a Cox regression model. MSI (P = 0.034), histological grade (P = 0.001) and the number of lymph nodes examined (P = 0.014) were identified as independent prognostic markers in this study.
Figure 1
Patients with higher TS gene expression in primary tumor cells had longer median relapse-free and overall survival (P = 0.030 and P = 0.029).
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In summary, patients with higher TS expression in the primary tumors, high frequency MSI, lower histological grades and more than 10 lymph nodes examined had better outcome after adjuvant chemotherapy.
Conflict of interests
The authors declare that they have no competing interests.
Acknowledgements
This work was supported by the grant from Science and Technology Agency of Henan Province government (05230303002).
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Authors' contributions
YL and SY designed the study, interpreted data; YL wrote the manuscript; QX and BW reviewed diagnoses of pathology; YJ performed the experiment; HG performed the statistical analysis; YH collected patient data and samples.
All authors have read and approved the final manuscript.
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