直肠癌术前放疗前后K-ras基因突变的研究

K-ras mutations in rectal cancer undergone preoperative radiotherapy

目的检测直肠癌术前放疗前后原癌基因Kirsten大鼠肉瘤病毒转化基因(K-ras基因)突变率的变化,从细胞遗传学方面深入研究放射治疗对直肠癌的作用。方法pTNMⅡ期和Ⅲ期直肠癌病人40例。病人术前行40Gy放疗,放疗前和术中分别取癌组织、距边缘2、4和6cm正常黏膜采用聚合酶链反应单链构象多态性分析(PCRSSCP)法检测K-ras基因第12密码子突变。结果癌组织中K-ras基因突变率显著高于癌周正常黏膜,同时距癌边缘2cm黏膜的K-ras基因突变率显著高于距癌边缘4、6cm黏膜的。放疗后癌组织和距癌边缘2cm黏膜的K-ras基因突变率与放疗前相比显著降低。结论距肿瘤2cm之内的黏膜有较高的K-ras基因突变率,向恶性转化的可能较大,放疗后癌组织和癌旁黏膜K-ras基因突变率显著降低,因此,放疗可能抑制癌旁黏膜恶变的早期事件,这可能是放疗能增加手术切除率和保肛率的原因。

Objective To detect K-ras mutations in rectal carcinoma before and after preoperative radiotherapy, and study genetics effect of radiotherapy in rectal cancer. Methods Forty patients with rectal cancer in pTNM stage Ⅱ or Ⅲ were enrolled. There were 20 males and 20 females. Sixteen tumours were pTNM Ⅱ stage, 24 pTNM Ⅲ. All patients received preoperative adjuvant radiotherapy. The treatment time is 4 weeks for 40 Gy in 2.0 Gy fractions and it is usually followed by an interval of 1-2 weeks before the operation. Tumor tissue and normal mucosa 2, 4, 6 cm to tumor were collected from patients before preoperative adjuvant radiotherapy and after operation. The K-ras mutations in codon 12 were investigated using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) in tumors and normal mucosa. Results The frequencies of K-ras mutations before preoperative adjuvant radiotherapy in tumor tissue and normal mucosa 2, 4, 6 cm to tumor were 47.5%, 22.5%, 2.5% and 0. The frequencies of K-ras mutations before preoperative adjuvant radiotherapy were higher in tumor tissue than in normal mucosa, and were higher in normal mucosa 2 cm to tumor than 4 cm and 6 cm to tumor. The postoperative frequencies of K-ras mutations in tumor tissue and normal mucosa 2 cm, 4 cm, 6 cm to tumor were 25.0%, 5.0%, 0 and 0.Compared to same locations of control group, the frequency of K-ras mutations in tumor tissue and normal mucosa 2 cm to tumor significantly decreased after radiotherapy. Conclusion Frequency of K-ras mutations of rectal cancer issue and normal mucosa 2 cm to tumor were significantly higher than other normal rectal mucosa, and decreased significantly after radiotherapy. So radiotherapy can inhibit early events of carcinogenesis of mucosa nearby tumor. It was the potential reason of increased rates of resection and sphincter-saving after radiotherapy.