The Mutation Rate Of K-ras And Related Factors In Colorectal Cancer

Background and objective:Colorectal cancer is one of the main cancers, which is a threat to human health. In China, the incidence of colorectal tumors in the digestive tract is ranked second. At present, the pathogenesis and development mechanism of the colorectal cancer is still unclear, the majority of scholars believe that the pathogenesis of colorectal cancer is together affected by internal factors (the genetic susceptibility of tumor) and external factors (dietary and environmental factors). A large number of experiments show that the occurrence of colorectal cancer is related to gene activation of oncogene or inactivation of tumor suppressor genes. Therefore reveal the molecular genetic changes in order to clarify the pathogenesis of colorectal cancer are the focus of the colorectal cancer study. And k-ras gene mutation is one of most common colorectal cancer-related genes. The k-ras gene mutation is considered to play the start role in the process of carcinogenesis, and also is an early case. At present, cetuximab which is a new tumor-targeted drug has been applied to treat metastatic colorectal cancer in the first-line. Whether k-ras gene mutation is related to the effects of cetuximab. Therefore k-ras gene expression status can be used as a predictor of treatment efficacy of cetuximab. k-ras gene becomes the first important molecular markers as targeted therapy for colorectal cancer. Therefore defining k-ras gene mutations status and related factors of the patients with colorectal cancer, not only in the pathogenesis of colorectal cancer research, but also in the treatment in colorectal cancer, have a vital role to play. The objective of this study is to detect k-ras gene mutations in colorectal cancer and to explore the k-ras gene mutation characteristics, as well as the relationship between mutation and clinical factors. Clinical material and method:47 colorectal cancer specimens are collected from patients with colorectal cancer in our hospital from 2008 to 2009. There are 5 patients with liver metastasis, and also collect the liver metastasis specimens. 52 specimens are made to paraffin-embedded tumor tissue in Pathology department at our hospital. 52 specimens are DNA sequenced by pyrosequencing technology in order to detect k-ras gene mutation type and mutation location.Results:(1)k-ras gene mutation: 16 cases were detected mutation in 47 cases of colorectal cancer specimens. The mutation rate was 34%. There were two intestinal specimens mutated in the five cases of liver metastasis of colorectal cancer, and it mutation rate was 40%. one of their liver metastases specimens also mutated, but the mutation of the other cases of liver metastasis specimens did not happen. The intestinal and liver metastasis specimens of the remaining 3 cases did not mutate. Occurred in 16 cases of k-ras mutant gene, there were 15 cases of mutation occurred in codon 12, another one occurred in codon 13. No mutation occurred in codon 61. (2)k-ras mutation and its correlation with age, sex, tumor depth of infiltration, histology type of tumor, lymph node metastasis, distant metastasis or Dukes stage: there were 47 cases of colorectal cancer patients with an average age of 62 years old, less than or equal to 62-year-old were 22 cases. There were 6 cases happened to mutation involve them, and its mutation rate was 27.3%; 10 cases happened to mutation in the 25 cases which ages were more than 62-year-old, and its mutation rate was 40.0%. There was no significant statistical difference between the two parts (P>0.05).There were 6 cases happened to mutation in the 26 male patients,its mutation rate was 23.1%; 10 cases happened to mutation in another 21 women, its mutation rate was 47.6%. There was no significant statistical difference between the two parts (P>0.05). Specimens in 47 cases, the depth of tumor infiltration limited to mucosa or muscularis were 6 cases, including 1 mutation, mutation rate was 16.7%; tumor infiltrate full thickness 41 cases, 15 cases happened to mutation, mutation rate was 36.6%. There was no significant statistical difference between the two parts (P>0.05). Specimens in 47 cases, there are 9 cases of well-differentiated type, two cases happened to mutation, mutation rate was 22.2%; 36 cases of differentiated type, 13 cases happened to mutation, mutation rate was 36.1%; two cases of poorly differentiated type, 1 case happened to mutation, mutation rate was 50%. There was no significant statistical difference between the three parts (P>0.05). 8 cases happened to mutation in the 19 case which existence of lymph node metastasis, its mutation rate was 42.1%; 8 cases happened to mutation with the other 28 cases without lymph node metastasis, its mutation rate was 28.6%. There was no significant statistical difference between the two parts (P>0.05). There were 5 cases of distant metastasis (liver metastasis) in 47 cases of colorectal cancer patients, and 2 cases happened to mutation. Its mutation rate was 40.0%; 14 cases happened to mutation in the other 42 cases which without distant metastasis, and its mutation rate was 33.3%. There was no significant statistical difference between the two parts (P>0.05). In 47 cases of patients with colorectal cancer, there are 5 Dukes A with no mutation; 23 Dukes B go with 8 cases mutation, and its mutation rate was 34.8%; 14 Dukes C go with 6 cases mutation, and its mutation rate was 42.9% ;5 Dukes D go with 2 cases mutation, the mutation rate was 40.0%. There was no significant statistical difference between them (P> 0.05).Conclusion:(1)The rate of k-ras gene mutation in colorectal cancer was 34%, and the mutations are mainly located in codon 12, followed by codon 13.(2)This study is the first time to detect the k-ras gene mutation of intestinal tumor and liver metastasis of tumor in the patients of colorectal cancer with liver metastases.We could conclude that the primary tumor k-ras genotypes and metastatic tumor k-ras genotypes are different.(3)The frequency of k-ras mutation is no correlated with age, sex, tumor depth of infiltration, histology type of tumor, Dukes stage, lymph node metastasis or distant metastasis.