Lack of Association between an XRCC1 Gene Polymorphism and Colorectal Cancer Survival in Thailand

Background: Colorectal cancer (CRC) is one of the most common causes of death worldwide and in Thailand. The X-ray repair cross-complementary protein 1 ( XRCC1 ) is required for efficient DNA repair. The effects of this gene on survival in colorectal cancer remain controversial and have not been reported in Thailand. The aim of this study was to investigate the association of the XRCC1 gene with survival of colorectal cancer patients in a Thai population. Materials and Methods: Data and blood samples were collected from 255 newly diagnosed and pathologically confirmed CRC patients who were recruited during the period 2002 to 2006 and whose vital status was followed up until 31 October, 2014. Real-time PCR-HRM was used for genotype identification. The Kaplan-Meier method, the log-rank test, and Cox proportional hazard regression were used to estimate cumulative survival curves and compare various survival distributions and adjusted hazard ratios. Results: Most of the cases were males, and the median age was 55 years. The median survival time was 2.43 years. The cumulative 1-, 3-, 5-, 7-, and 10 year survival rates were 76.70%, 39.25%, 26.50%, 16.60% and 3.56%, respectively. After adjustment, female gender, ages 50-59 and ≥ 60 years, tumour stage III+IV, a signet-ring cell carcinoma, and poor differentiation had significant associations with increased risk of CRC death. While the XRCC1 Arg/Arg homozygote appeared to be a risk factor for CRC death, the association was not significant. Conclusions: The genetic variant in the XRCC1 may not be associated with the survival of CRC patients in Thailand. Further studies are needed to verify our findings.


Introduction
Colorectal cancer (CRC) is the third-most common cancer in the world, and in 2012 there were estimated to have been more than 746,298 newly diagnosed cases and more than 373,639 deaths due to the disease globally (Ferlay et al., 2015). In Europe and the United States of America the colorectal incidence rates are trending down (Rahib et al., 2014;Malvezzi et al., 2015), but in Asia the rates are trending up (Pourhoseingholi, 2012). This is also the case in Thailand where CRC is the fifth most common of all malignant tumors, and the age-standardized incidence rates (ASR) are estimated to be 15.2 per 100,000 for males and 10.1 per 100,000 for females (Khuhaprema drinking alcohol, smoking and lack of physical activity are risk factors, particularly when there is a defective DNA repair gene. The X-ray repair cross-complementary protein 1 (XRCC1) is a single nucleotide polymorphism (SNP) which was initially discovered through its role in the repair of DNA damage caused by ionizing radiation (Brem and Hall, 2005). However, SNPs in XRCC1 may impair the efficiency of XRCC1 in DNA repair activity, especially in base excision repair (BER) and singlestrand break repair processes. The presence of a SNP in XRCC1 is also relevant to cancer (Shen et al., 2011). The polymorphisms of the XRCC1 gene in humans consist of Arg 194Trp, Arg280His and Arg399Gln. Many studies have suggested that XRCC1Arg399Gln is associated with either increased or decreased risk for several types of cancers (Goode et al., 2002;Zhou et al., 2003;Yi et al., 2013), and XRCC1 Arg399Gln has been shown to increase the risk for CRC (Yeh et al., 2007;Kabziski et al., 2010;Yin et al., 2012;Zeng et al., 2012;Tian et al., 2013;Poomphakwaen et al., 2014;Dai et al., 2015). Differences in survival rates in CRC depend on factors called clinicopathological characteristics; these comprise tumor site, stage of the disease (TNM, Dukes' staging system), histological type, histological grading, type of treatment and sites of any metastases site (Elsaleh et al., 2000;Laohavinij, Maneechavakajorn & Techatanol, 2010;Zhang et al., 2010).
While the potential association of XRCC1 polymorphisms with survival has been studied in a variety of cancers (Yoon et al., 2005;Bewick et al., 2006;Liu et al., 2007;Miao et al., 2012;Putthanachote et al., 2014), only a few studies have investigated the association between XRCC1 Arg399Gln and survival in colorectal cancer, and the results of these remain controversial. In addition, no study has been published about the role of XRCC1 polymorphisms in CRC survival among Thai people.
The purpose of this study was to investigate the association between XRCC1 Gene polymorphisms and colorectal cancer survival in a Thai population.

Subjects and data collection
This is a retrospective cohort study in which the subjects were a consecutive series of newly diagnosed CRC patients admitted during the period from October, 2002, to October, 2006, to Srinagarind Hospital, the main teaching facility of the Faculty of Medicine, Khon Kaen University, and to Khon Kaen Regional Hospital. All had been diagnosed in accordance with the International Classification of Diseases for Oncology (ICD-O, 3 rd edition, 1st revision), and all diagnoses were histologically confirmed.
When CRC cases with multiple primary malignant tumors were excluded, 255 patients were recruited, and all were followed up until death or the end of the study (31 October, 2014). Survival time was defined as the time elapsing between diagnosis and either death or the end the study. Information about prognostic factors known from previous studies to be related to the CRC patients was retrieved from medical records; these prognostic factors were age at diagnosis, gender, tumor site, stage of the disease (TNM, Dukes' staging system), histological type, histological grading, and type of treatment. The XRCC1 genotypes were retrieved from laboratory records (laboratory procedures described below).
The vital status of each patient was monitored from medical records and by linkage with the death registry of the Thai national statistics database.

Laboratory methods
Whole blood samples (3-5ml) were taken from all the recruited CRC patients, and these were centrifuged at 3,000 rpm for 15 minutes to separate plasma, buffy coat and red blood cells. All specimens were kept at -20 o C at the Cancer Unit in the Faculty of Medicine, Khon Kaen University. The genomic DNA was extracted from the buffy coat at Nagoya City University Medical School, Japan.

PCR amplification and detection of genetic polymorphisms
A real-time polymerase chain reaction with high resolution melting technique (Real-time PCR-HRM) was performed in order to identify the XRCC1 polymorphisms. DNA amplification was performed in a 96-well plate in a LightCycler® 480 Real-Time PCR System. The amplification of XRCC1 Gln399Arg gene used two primers, forward: 5 ́-AGT GGG TGC TGG ACT GTC-3 ́ and reverse:5 ́-TTG CCC AGC ACA GGA TAA-3 ́. The HRM data were analyzed using the LightCycler® 480 Gene Scanning software version 1.5 (Roche) in the Department of Microbiology, Faculty of Medicine, Khon Kaen University. To assess and validate genotyping quality, a PCR-restriction fragment length polymorphism analysis (PCR-RFLP) was performed in approximately 10% of random samples.

Statistical analysis
Categorical data were reported as numbers and percentages, and continuous data were summarised in the form of means with standard deviations or medians with ranges (minimum : maximum). Observed survival rates were calculated from a Kaplan-Meier survival curve, and the rates were presented as percentages of patients who were alive after a certain period of time with 95% confidence intervals (95% CIs).
The log-rank test was used to compare the survival distributions in two or more groups. The associations between survival and the various prognostic factors were analysed using Cox proportional hazard regression models with the results reported in terms of crude and adjusted hazard ratios (HRadj) and their 95%CIs. Factors reaching a p<0.25 level of significance in the univariate analysis in the initial model and other factors found to have significant association with CRC survival in previous studies were included as candidate variables a multivariate analysis using backward elimination.
All analyses were conducted using Stata version 10.0 (Stata Corp LP, 2007). Except for the process of selecting variables to be included in the multivariate analysis, statistical significance was set as p<0.05.

Ethical Consideration
The study was approved by the Khon Kaen University Ethics Committee for Human Research (reference number: HE581400).

Characteristics of CRC patients
The general and pathological characteristics of the 255 CRC patients are summarised in Table 1. Most of the cases were males, and the median age was 55 years. The most common tumor site, stage and treatments were the colon (NOS), stage III, and surgery, respectively. By far the most frequently reported histological type of malignancy was adenocarcinoma, and for most patients the tumor cells were graded as well-differentiated. Regarding the prevalence of XRCC1 polymorphisms, Arg/Arg were found slightly more often than Gln/Arg. Asian Pacific Journal of Cancer Prevention, Vol 17, 2016 2057 DOI:http://dx.doi.org/10.7314/APJCP.2016.17.4.2055 Lack of Association between XRCC1 Gene Polymorphism andColorectal Cancer Survival in Thailand Survival rate of CRC patients For the 255 CRC cases, the overall follow-up persontime was 570 person-years, and the overall mortality rate was 28 per 100 person-years (95% CI= 24.17 to 32.92). The cumulative 1-,3-,5-,7-, and 10 years survival rates were 76.70%, 39.25%, 26.50%, 16.60% and 3.56%, respectively (Table 2). Figure 1 shows the median survival time of all CRC patients, which was 2.43 years (95% CI: 1.88 to 2.83). The survival times by stage of disease, histological type and XRCC1 polymorphisms are presented in Figures 2-4. When the stages were grouped as stage I+II and stage III+IV, the median survival times were 5.08 years and 1.57 years, respectively. The median survival times for the histological types of adenocarcinoma, mucinous and signet-ring cell were 2.45, 2.50 and 1.09 years, respectively. The median survival times for patients with the Arg/Arg, Gln/Arg and Gln/    Gln polymorphisms were 2.20, 2.55, and 2.67 years, respectively.

Discussion
In Asia, including Thailand, the incidence of CRC has dramatically increased in recent years. The main objective of this study was to investigate the association between XRCC1 gene polymorphism and CRC survival in Thailand, and this is the first analytic study to explore features of XRCC1 gene polymorphisms as possible death factors in a Thai population of CRC patients.
Our findings indicate that the XRCC1 polymorphisms of Arg/Arg, Gln/Arg and Gln/Gln have no association with survival of CRC patients. This is consistent with the conclusions of studies in Germany and Korea (Grimminger et al., 2010;Kim et al., 2010). It also in line with another study in Thailand which found that the genetic variant Gln339Arg in XRCC1 made no statistically significant contribution to risk of death among Thai patients with stomach cancer (Putthanachote et al., 2014). However, there are differences in physiology and anatomy, environmental carcinogens, genetic mechanisms, and prognosis between the three segments of the bowel: the proximal and distal colon and the rectum (Li & Lai, 2009). For example, a study in Taiwan, explored differences in survival between colon and rectal cancers in terms of associations with XRCC1 polymorphisms. Rectal cancer patients with XRCC1 Arg/Gln + Gln/Gln appeared to be at less risk of rectal cancer death when compared with patients who had Arg/Arg. In contrast, colon cancer patients with XRCC1 Arg/Gln + Gln/Gln appeared to be at greater risk of colon cancer death when compared with patients who have Arg/Arg. These findings were not statistically significant, but they raise important issues about potential differences due to CRC site (Lai et al., 2013).
Normally, it is male gender which is associated with an increased risk of CRC death (for example, the Japanese study by Watanabe et al., 2001). However, in our study, female patients were at higher risk of CRC death than males; one possible explanation for this is that more of the female patients (77.06%) were at late stages of the disease (stages III+IV) than were the males (61.74%). This finding was supported by a Saudi Arabian study, but only for rectal cancer (Al-Ahwal et al., 2013). Not surprisingly, we found ages 50-59 and ≥60 years, tumor stage III+IV, a signet-ring cell carcinoma, and poor differentiation had a significant association with increased risk of CRC death. Similar findings have been previously reported worldwide (Halvorsen and Seim, 1989;Jen et al., 1994;Takebayashi, Aklyama, Yamada, Akiba, & Aikou, 1996;Dignam et al., 2003;Koo et al., 2008;Schetter, Leung S, Sohn et al,, 2008;Laohavinij, Maneechavakajorn & Techatanol, 2010;Nitsche et al., 2013). It is noted that the finding regarding the signet ring cell carcinoma arose despite the fact that this histological type is less common than adenocarcinoma (O'Connell et al., 2004).
The 5-year survival rate of CRC patients in our study was 26.50%. This rate was lower than that found in previous studies reported in Thailand. In 1995, (Sriamporn et al., 1995Laohavinij et al., 2010) the reported 5-year survival rates for CRC patients were 36.8% and 38.6%, respectively, and another study (Berberoglu U, 2004) reported that the 5-year survival was even higher (62%). Our 5-year survival rate is probably low because we obtained data from a tertiary hospital where most of patients were at late stages. Moreover, all the CRC cases in our study were confirmed histologically which means that other conditions with better prognoses were excluded.
Our study did have some limitations. Due to budget and time constraints, we studied only the effect of XRCC1 Arg399Gln on survival of CRC patients, and this gene is only one type of the various components in the DNA repair process.
In conclusion, while gender, age, stages of disease, histological type (signet-ring cell) and histological grading (poorly differentiated) were factors affecting survival of CRC in a Thai population, no significant differences were founded in the effect of XRCC1 Arg399Gln polymorphisms on CRC survival. There is, however, a need for further research to confirm our findings, investigate related issues and explore differences and possible interactions in the way which XRCC1 polymorphisms affect CRC survival between the three different segments of the bowel.