To our knowledge, this is the first study which has investigated whether GRP78 rs391957 and rs430397 polymorphisms are associated with the risk of CRC. In this hospital-based case-control study, we found that the CT heterozygous, TT homozygous and combined (CT+TT) genotypes of GRP78 rs391957 polymorphism and the GA heterozygous, AA homozygous and combined (GA+AA) genotypes of GRP78 rs430397 polymorphism were both significantly associated with higher risk of CRC in a Chinese Han population, suggesting that the two GRP78 polymorphisms probably play potential roles in the development of CRC.
In the USA, new cases with rectal cancer accounted for approximately 40% of cases with CRC 
. However, we found that 75% CRCs occurred in the rectum in our cases, which was inconsistent with rectal cancer accounting for 40–50% in overall Han population. Our data was similar to that of the previous study about southwestern Chinese population by Wang et al.
where 77% CRCs were rectal cancers in their cases 
. One possible explanation is the incidence of cancer should be region-specific. Due to the vast territory and large population in China, life style and economic development are different in different regions, with different morbidities for different cancers. For this reason, now that our study focused on southwestern Han population in China, the high proportion of rectal cancer in our cases which might reveal the epidemiological situation of CRC in southwestern Han population was probably different from the proportion of rectal cancer in overall Han population. On the other hand, as southwest China is an economically underdeveloped area, the majority of people in southwest China are unable to afford routine screening for CRC. Therefore, most diagnosed cases were presented as symptomatic diseases. While rectal cancer may be more obvious than non-rectal colon cancer, patients with rectal cancer have a greater possibility of getting examination and treatment than those with non-rectal colon cancer. This may be another reason for high proportion of rectal cancer in our cases. Yet despite all this, the definitely proportions of rectal cancer and non-rectal cancer in southwestern Han population would need further investigation in large and multiple-centers studies. Additionally, the ratio of males to females with CRC in our study was 1.39
1, which was also similar to that of 1.36
1 in the previous study about southwestern Chinese population by Wang et al.
. Although our ratio in CRC was higher than that in the USA which is usually well balanced between males and females, we considered that the gender ration should also be region-specific because of differences in risk behaviors and ethnic groups. The previous study which showed the lower rates observed among females compared with males may be related to differences in risk behaviors associated with colorectal cancer, such as smoking, and the differing effect of obesity in men and women, also pointed at it 
. Thus, the higher ratio of males to females with CRC might be the representative of gender ratio in southwestern Chinese population.
It is clear that overexpression of GRP78 occurs in various human cancers and cancer cell lines, correlating with malignancy, metastasis and poor prognosis 
. The elevated expression of GRP78 increased the WHO pathologic grade of primary astrocytoma, which strongly predicted the patients’ prognosis 
. The expression of GRP78 was up-regulated in prostate cancer cells compared with benign tissue, and the patients with higher expression of GRP78 had almost twice the risk of dying from prostate cancer compared with those with weak expression 
. GRP78 was highly expressed in gastric cancer and appeared to be an independent survival predictor 
. One previous study reported that overexpression of GRP78 appeared to correlate with histological severity from the normal colon tissue to colon adenoma to colon carcinoma, which indicated that overexpression of GRP78 might be a marker for malignant transformation of CRC 
. Furthermore, another study showed that knockdown of GRP78 inhibited the proliferation of CRC cells and increased the apoptosis of CRC cells in vitro, which indicated that the expression of GRP78 might enhance the proliferation of CRC cells and protect them against apoptosis 
Several studies have demonstrated that the polymorphisms in the promoter of gene are likely to enhance or attenuate the expression of gene 
. The rs391957 polymorphism is located in the promoter of GRP78 gene 
. It has been noted that the rs391957 polymorphism altered the expression of GRP78 in cells under different conditions. Specifically, in normal cells, the variant T allele carriers had lower basal promoter activity than the CC homozygous carriers. However, in cells under the condition of ER stress, the variant T allele carriers had significantly higher expression of GRP78 than the CC homozygous carriers 
. Thus, the variant T allele of GRP78 rs391957 polymorphism probably enhances the expression of GRP78 in various cancers thereby affecting the development and progression of cancers. These findings are consistent with the previous study which showed that the CRC patients with the CT heterozygous or TT homozygous genotypes had a significantly higher risk of tumor recurrence compared with the patients with the CC homozygous genotype 
. Subsequently, our present study has similar findings, which showed that the variant T allele carriers had higher risk of CRC compared with the wild C allele carriers. Collectively, these data provide preliminary support that the variant T allele of GRP78 rs391957 polymorphism may be both a susceptible marker and a prognostic marker for CRC, and have an important function in the development and progression of CRC due to enhancing the expression of GRP78. However, some results still remain contradictive. The latest study showed that the C allele of GRP78 rs391957 polymorphism was associated with increased risk of HCC and the C allele carriers had higher mRNA and protein expression of GRP78 in HCC 
. The possible explanation is that the conditions of ER stress are different in various types of cancer. Thus, more and further investigations are needed to discover and confirm the roles of GRP78 rs391957 polymorphism.
We also found that the variant T allele of GRP78 rs391957 polymorphism was associated with local tumor invasion of CRC. However, due to the retrospective design and relative numbers of cases involved, further prospective biomarker embedded clinical trials and cell and tissue experiments will be necessary to validate our result and identify what role the rs391957 polymorphism plays in progression of CRC. In our study, T4 stage was the majority of the cases. Tumor stage is often associated with lack of screening, access to medical care and so on. Thus, our result might also reveal that there is a lack of screening for CRC in southwestern Chinese population. Patients with CRC were unable to get prompt diagnosis, so that the majority of them were at advanced stages when they received proper treatment. It is necessary that southwestern Chinese pay more attention to routine screening for CRC. In addition, the previous study found higher expression of GRP78 contributed to increased lymph node metastasis in gastric cancer patients 
. In contrast, we found the CRC patients with the variant T allele contributing to higher expression of GRP78 might have less possibility of lymph node metastasis. Limitations of our small sample size are likely to be the reason. Alternatively, the roles of GRP78 in affecting status of lymph node metastasis are different in various cancers.
The variant T allele frequency is approximately 29% in Asian population, 36% in European population, 29% in the USA and only 9% in African population. Thus the fact that most populations share similar proportions of T carriers reinforces the importance of our findings and the need for further study. However, ethnicity is of major importance in polymorphism analysis, and our findings also need studies about other ethnic populations to confirm it in the future.
The polymorphisms in the intron of gene have received less attention, but are beginning to be recognized for their potential contribution to the development and progression of diseases, including cancers 
. There are splicing enhancer and splicing silencing sites throughout the introns of genes. Sequence alterations in any of these intronic sites can lead to alteration in splicing of the pre-mRNA which contributes to malignant progression 
. The rs430397 polymorphism is just located in upstream from the intron/exon boundary within the fifth intron of GRP78 gene 
. The previous study has firstly demonstrated that the variant A allele of GRP78 rs430397 polymorphism was associated with higher risk and poor prognosis of hepatocellular carcinoma 
. Another study has also demonstrated that the AA homozygous carriers had higher RNA and protein expression of GRP78 compared with the GG homozygous carriers in tissues, and that the AA carriers had poor prognosis of non-small cell lung cancer 
. The mechanism of GRP78 rs430397 polymorphism affecting the development and progression of cancer is unclear. One hypothesis is that this allele variation in the intron probably alters the splicing of the pre-mRNA, thereby affecting the expression of GRP78 by altering the efficiency of translation or mRNA stability 
. The result of our study which showed that the variant A allele carriers had higher risk of CRC compared to the CC homozygous carriers has provided indirect evidences to support the hypothesis. Therefore, the variant A allele may be able to enhance the expression of GRP78, but the further function investigation is needed to explain the precise mechanism. Furthermore, the variant A allele of GRP78 rs430397 polymorphism may be a susceptible marker for CRC, but whether the variant A allele is associated with the prognosis of CRC is still not known.
There have been approximately 200 known polymorphisms within the GRP78 gene 
. Based on previous studies, the polymorphisms of rs391957 and rs3216733 were completely linked 
, and the polymorphisms of rs391957, rs17840761 and rs12009 were in linkage disequilibrium while the haplotypes of them were not associated with CRC 
. Furthermore, the polymorphisms of rs17840761 and rs12009 were not associated with CRC 
. Additionally, it was not found that other polymorphisms and rs430397 polymorphism were in linkage disequilibrium.
There were significant associations between the risk of CRC and the GRP78 rs391957 and rs430397 polymorphisms. Both the variant T allele of rs391957 polymorphism and the variant A allele of rs430397 polymorphism were associated with higher risk of CRC in southwestern Chinese Han population, though whether the variant T allele of rs391957 polymorphism affected local tumor invasion stages and status of lymph node metastasis needs to be further tested in prospective larger-scale studies in the future. These preliminary findings suggested that the GRP78 polymorphisms could provide clues to forecast susceptibility to CRC. But the precise mechanisms underlying the relationship of the GRP78 polymorphisms and CRC also need further investigation.