胃肠道间质瘤60例中c-kit和PDGFRA基因突变的检测

目的:探讨c-kit基因和PDGFRA基因在我国胃肠道间质瘤(GIST)中的突变状况.方法:用PCR扩增和直接测序的方法,检测60例GIST c-kit基因9号、11号、13号和17号外显子突变以及PDGFRA基因12号和18外显子突变.结果:60例GIST中kit基因突变率为63.3%,绝大多数为杂合性突变,少数为纯合性突变.其中以编码近膜区的11号外显子突变最为常见(58.3%);其次为编码胞外区的9号外显子突变(3.3%);偶见编码胞内酪氨酸激酶结构域的13号外显子突变(1.7%),是一个新的突变位点L641P;未检出17号外显子突变.11号外显子的突变位点多集中在5'端的经典热点(42.9%),表现为密码子第557-560的点突变和框内缺失.第二个热点位于11号外显子的3'端,为框内串联重复.后者主要发生在胃部,女性患者多见.60例GIST中PDGFRA基因突变率为5%,表现为编码胞内酪氨酸激酶结构域的18号外显子D842V点突变,且均为CD117阴性.未见编码近膜区的12号外显子突变.结论:CD117阳性GIST主要表现为c-kit突变,分布在11号外显子经典热点和3'端热点,后者与老年女性胃GIST相关.PDGFRA基因突变主要见于CD117阴性GIST,多发生在后腹膜,具高度侵袭危险性.

c-kit and PDGFRA mutations in 60 cases of gastrointestinal stromal tumors (GISTs)

OBJECTIVE: To explore the status of activating mutations of c-kit and PDGFRA in GIST of Chinese patients. METHODS: Sixty GISTs, confirmed by immunoreactivity of CD117, CD34, SMA, S-100 and Desmin, were evaluated for the presence of c-kit exons 9, 11, 13 and 17 mutations, and PDGFRA exons 12 and 18 mutations. The PCR products were sequenced directly for mutations, using DNA extracted from paraffin-embedded tissue. RESULTS: 53% of the tumors were located in the stomach, 22% in the small bowel, 8% in the colo rectum, 2% in the esophagus and 15% in the extragastrointestinal tract. Immunohistochemical demonstrations of c-kit (CD117) were seen in 90% cases. Overall, c-kit mutations were detected in 63.3% of patients as follows: 58.3% in exon 11, 3.3% in exon 9, 1.7% in exon 13 and none in exon 17. The types of c-kit exon 11 mutations were mostly heterogeneous and clustered in the classic "hot spot" at the 5' end of exon 11, 42.9% being point mutation and in-frame deletion at Codon 557-560. 14.3% of cases showed internal tandem duplications (ITD) at the 3' end of exon 11 in a region of a second hot spot for c-kit mutations. Interestingly, these cases were associated with female predominance, stomach location and occurrence in older patients. The present study failed to identify a significant association between c-kit mutation status and risk of aggressive behavior in GISTs. Exon 9 mutations consisted of ITP of six nucleotides encoding Ala-Tyr. A new point mutation of L641P was revealed in exon 13. PDGFRA mutations were found in 5% of all the 60 cases with none of the positive cases expressed detectable KIT protein. The type of mutation was the commonest point mutation of D842V of exon 18. CONCLUSION: Most KIT expressing GIST show c-kit mutations that are preferentially located within the classic hot spot of exon 11. A second hot spot -ITD at the 3' end of exon 11 seems to associate with a subgroup of gastric GISTs in older females. c-kit exons 9, 13 and 17 mutations are rare events in GIST of China. PDGFRA oncogenic mutations are more likely seen in KIT-negative GISTs arising in the peritoneal surface and have an unfavorable clinical course.