胶质瘤中异柠檬酸脱氢酶基因的检测及其对化疗疗效的影响
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摘要
第一部分：胶质瘤患者异柠檬酸脱氢酶基因突变的检测及其临床意义
研究背景和目的
由星形细胞、少突胶质细胞、室管膜细胞等神经胶质细胞起源的胶质瘤是CNS最常见的恶性肿瘤,其生长部位、病理形态、基因遗传学改变和治疗效果有很大的差异性,通常依照其病理组织学类型分为低级别胶质瘤(WHO Ⅰ～Ⅱ级)和高级别胶质瘤(WHOⅢ～Ⅳ级)。胶质瘤呈浸润性生长,与正常脑组织界限不清,仅靠手术难以治愈,以最大程度上的手术切除为基础,结合放疗和化疗的综合治疗以延缓肿瘤复发和延长患者的生存期。尽管如此,WHOⅢ级胶质瘤者生存期一般才2-3年,而WHO Ⅳ级如胶质母细胞瘤(Glioblastoma,GBM)患者生存期仅为1年左右。胶质瘤患者的病死率居高不下,使其成为中枢神经系统(Central nervous system,CNS)最难攻克的肿瘤。令人庆幸的是,分子生物学的迅速发展给神经肿瘤学研究带来了一场深刻的变革,特别是胶质瘤的基础研究和临床研究的所有领域。随着人们对肿瘤的分子遗传学和表观遗传学认识不断提高,以及肿瘤分子流行病学、分子病理学等新兴学科的建立,CNS肿瘤发生、增殖、侵袭和血管形成的分子机制不断被揭示,同时也为开发各种分子靶向治疗药物提供了重要的理论基础。
最新的突破发生在2008年,Parsons等学者为了鉴定GBM的基因遗传学改变,对GBM的20661个蛋白的编码基因进行测序,在世界上首次发现了异柠檬酸脱氢酶1的编码基因(isocitrate dehydrogenase1, IDH1)突变存在于胶质瘤中。实验发现在149位GBM患者中有18位(12%)存在IDH1突变,且所有的IDH1突变都是发生在第四外显子的Arg132(R132)的氨基酸序列上,该项成果发表在当年的SCIENCE杂志上。Balss J等在685例包含了各种类型不同病理级别的胶质瘤中更大范围研究了IDH1的R132突变。IDⅢ突变在胶质瘤中频繁发生,其在弥漫性星形细胞瘤(WHO Ⅱ级)中发生率为68%,而在继发性GBM (Secondary glioblastoma, sGBM)中发生率达到88%。此外,少突胶质细胞瘤和少突胶质星形细胞瘤中的IDH1突变发生率分别为69%和78%,而在毛细胞性星形细胞瘤(WHO Ⅰ级)中没有检测到IDH1/2突变。2009年新英格兰杂志上发表了美国杜克大学HaiYan等的文章,研究者们在445个CNS肿瘤和494个非CNS肿瘤中进行了IDH1和IDH2的基因突变检测,发现IDH1突变不仅仅存在于WHOⅣ级GBM中,也广泛存在于WHO Ⅱ级、Ⅲ级的星形细胞瘤和少突胶质细胞瘤中。在445个CNS肿瘤样本中检测到了161个IDH1的R132突变,在毛细胞性星形细胞瘤、室管膜下巨细胞瘤(WHO Ⅰ级)、室管膜瘤(WHO Ⅱ级)、髓母细胞瘤及其他非CNS肿瘤中均没有检测到IDH1突变。随后胶质瘤相关的IDH突变被的其他中心的一些学者相继研究证实,揭示了IDH1/2突变与患者的年龄,病理类型以及临床预后的关系,并且发现IDH突变与其他胶质瘤分子标记物比如TP53突变,表皮生长因子受体基因(Epithelial growth factor receptor gene, EGFR)扩增,BRAF fusion基因,1p19q杂合性缺损以及O6-甲基鸟嘌呤-DNA甲基转移酶(O(6)-methylguanine DNA methyltransferase, MGMT)启动子甲基化都有一定的相关性。
但是在本实验完成之前尚未有针对中国人群中胶质瘤患者的IDH突变的相关报道。那么,在中国人群胶质瘤患者中是否同样存在IDH突变?其发生率与欧美国家的研究结果是否有差异?IDH突变与胶质瘤患者同步放化疗(Concomitant chemoradiotherapy, CCRT)的疗效有没有关联?本研究旨在通过聚合酶链反应—高分辨率熔解分析方法和直接测序的方法检测中国人群胶质瘤患者IDH突变情况,并与国外文献报道的结果进行比较。另外本研究也初步探讨了IDH突变与胶质瘤患者CCRT效果的关系。
方法
研究对象
收集南方医科大学南方医院神经外科203例中国人群胶质瘤患者的肿瘤标本(包括各个WHO级别和不同的病理类型),所有的肿瘤标本都取自本院病理科的石蜡包埋组织,而患者的临床资料来自南方医院电子病历系统的病历记录。所有肿瘤标本均先经两位以上病理科医生进行病理确认,取含有肿瘤细胞最多的部分组织做切片。患者的临床资料包括年龄、性别、病理诊断、健康状况评分(WHO-performance scale, WHO-PS)、手术切除程度、术后辅助治疗情况(放疗、化疗或者CCRT)、确诊日期、手术日期、复发日期、死亡日期、最后一次随访日期以及最后一次随访时患者的生存状态。术后CCRT的方案是国际上的标准方案即Stupp方案：放疗的整个疗程应同步化疗,口服替莫唑胺(Temozolomide, TMZ)75mg/m2,疗程42d。放疗结束后2-4周,辅助TMZ治疗150mg/m2,连续用药5天,28d为一个疗程,若耐受良好,则在以后化疗疗程中增量至200mg/m2,推荐辅助TMZ化疗6-12个疗程。采用聚合酶链反应—高分辨率熔解分析方法及直接测序法检测IDH1和IDH2突变情况,研究IDH突变与患者临床预后之间的关系。
统计学处理
所有统计学计算均使用SPSS13.0软件完成。计数资料采用卡方检验进行差异性检验,独立样本T检验用来分析IDH突变阳性组和IDH突变阴性组的年龄差别。无进展生存期(Progression-free survival, PFS)和总体生存期(Overall survival, OS)用来反映患者的预后情况。PFS和OS用来反映患者的临床预后,两者均以手术当天为第一天开始计算,前者到患者病情进展确诊的当天结束,后者到患者死亡当天或者最后一次随访结束(删失数据)。应用Kaplan-Meier法行生存分析、Log-rank法行显著性检验以比较不同患者的生存差异,以P<0.05为差异有统计学意义。需要注意的是,高级别胶质瘤患者术后2周之内死亡或者低级别胶质瘤患者术后2月之内死亡不纳入生存分析中,因为其死亡可能是手术的并发症所致,不是疾病的自然进程。
结果
203例胶质瘤患者中(包括WHO Ⅰ级5例：毛细胞型星形细胞瘤5例；WHOⅡ级86例：节细胞胶质瘤4例,弥漫性星形细胞瘤60例,少突胶质细胞瘤8例,少突胶质星形细胞瘤14例；WHOⅢ级67例：间变性星形细胞瘤49例,间变性少突胶质星形细胞瘤11例,间变性少突胶质细胞瘤7例；WHOIV级45例：pGBM38例,sGBM7例)有80例存在IDH突变,其中IDH1突变75例(36.9%)、IDH2突变5例(2.5%)。没有一例样本同时存在IDH1和IDH2两种突变。IDH突变型患者较IDH野生型患者年龄更年轻,手术的全切率更高。分组讨论中(主要分为：除外WHO Ⅰ级毛细胞型星形细胞瘤的整体组,WHOⅡ级无术后辅助治疗亚组,WHOⅢ级术后行CCRT亚组),无论是在除外5例WHO Ⅰ级患者的总体上比较(P<0.001),还是在WHO Ⅱ级无术后辅助治疗的患者组(P=0.014)以及在WHOⅢ级术后行CCRT组内(P=0.033)比较,IDH突变阳性患者的OS比IDH突变阴性患者的OS长。另外在WHOⅢ级术后行CCRT组,IDH突变与CCRT疗效无相关性。
结论
IDH突变同样广泛存在于中国人群胶质瘤患者中(WHOⅡ～Ⅲ级的胶质瘤以及WHOⅣ级的sGBM),但IDH1突变率却稍低于欧美国家研究中心的报道,IDH1/2的突变类型也少于以往国外的报道。本组数据也再次证实了IDH突变型患者预后相对IDH野生型患者较好,但是IDH突变在间变性胶质瘤中与患者术后CCRT的疗效无相关性。
第二部分：异柠檬酸脱氢酶基因突变在继发性胶质母细胞瘤中与替莫唑胺疗效的关系
研究背景和目的
GBM是成年人中最常见、恶性程度最高的脑肿瘤,也是恶性胶质瘤中最常见的类型(约一半以上),其年发病率约3-5/10万人,可发生在任何年龄段,最常发生在老年人(年龄的中位数为64岁,sGBM患者发病年龄要稍年轻,年龄的中位数为45岁),很少发生在儿童患者。GBM具有很高的致残和致死率,严重威胁人类健康,而其治疗前景至今仍然不容乐观。即使经过最大程度上的手术切除和术后规范的CCRT, GBM患者的中位PFS和OS也仅仅只有7个月和15个月。GBM呈浸润性生长,具有特征性的病理组织学特点和影像学特点。90%以上的GBM是原发性的(Primary Glioblastoma multiforme, pGBM),进展很快,病程从几天到几周不等。约10%的GBM是继发性的,是由WHO Ⅱ或Ⅲ级胶质瘤逐渐进展而来。pGBM和sGBM虽然在病理组织学上很难区分,但是两者具有截然不同的分子生物学转导通路。近几年来越来越多的研究结果表明IDH1和IDH2突变广泛存在于sGBM中。
在GBM中MGMT启动子甲基化不仅仅是患者临床预后的良性指标,更是预测TMZ疗效的敏感指标。而在间变性胶质瘤中,MGMT启动子甲基化仅仅是一个良性预后指标,与TMZ的疗效无关。事实上MGMT启动子甲基化作为预测TMZ疗效的敏感指标主要是针对于新诊断的GBM,而新诊断的GBM中约90%是原发性,继发性的只占到10%左右。然而如前所述,pGBM和sGBM虽然在病理组织学上很难区分,但是两者发病的分子生物学机制截然不同,因此很难说MGMT启动子甲基化在sGBM中扮演着同样的角色。另外在sGBM中,MGMT启动子甲基化往往和IDH1/2突变同时存在,而H1/2也是胶质瘤患预后的强有力的预测指标,那么在sGBM患者临床预后方面,MGMT启动子甲基化与IDH1/2的关系如何?孰轻孰重?还有在sGBM患者中,在TMZ疗效方面,MGMT启动子甲基化与IDH1/2的关系又如何?我们查阅国内外文献,尚没有这方面的报道。本研究目的是探讨IDH突变对sGBM患者TMZ化疗临床预后的影响,以及与其他分子标记物如p53表达、MGMT启动子甲基化、1p19q杂合性缺失的关系。
方法
研究对象
收集2003年1月至2009年12月经手术证实的sGBM86例,分别检测IDH1/2突变、1p19q杂合性缺失、MGMT启动子甲基化和p53表达,利用生存分析比较这些指标与患者临床预后(即PFS和OS)的关系。反映TMZ疗效的主要指标是用药后的患者PFS和肿瘤大小(通过定期的头颅磁共振检查来反映)。
统计学处理
各项分子标记物指标之间的相关性以及各项分子标记物指标与TMZ疗效(主要是通过影像学上的改变来反映)的关系用卡方检验(其中多重比较用Bonferroni检测法)。独立样本T检验用来分析IDH突变阳性组和IDH突变阴性组的年龄差别。PFS和OS用来反映患者的临床预后,两者均从使用TMZ的第一天开始计算,前者到患者病情进展确诊的当天结束,后者到患者死亡当天或者最后一次随访结束(删失数据)。应用Kaplan-Meier法行生存分析、Log-rank法行显著性检验以比较不同患者的生存差异。进行多变量分析以了解各因素对生存期的影响,本研究中使用Cox比例风险回归模型来估计风险比(HR),并计算95%可信区间(CI)和P值,运用逐步回归法进行各因素的筛选及最优模型的建立。以上统计学方法均采用双尾检验,检验水准α取0.05,数据的分析均采用SPSS13.0版本。
结果
79例患者中有58例存在IDH1或者IDH2突变(突变率73.4%,7例肿瘤样本无法检测)。IDH突变、MGMT启动子甲基化以及1p19q杂合性缺失均与患者的PFS呈正相关。IDH突变阳性或者MGMT启动子甲基化的患者对TMZ的疗效更好,主要反映在相同的时间内肿瘤体积的缩小更明显。IDH突变阳性和MGMT甲基化同时存在的患者,TMZ治疗的效果最好。
结论
本研究通过对86例sGBM的各项分子标记物指标检测,结合随访以及系统的生存分析得出以下结论：
IDH突变是sGBM TMZ化疗疗效的一个有效的预测指标,即IDH突变阳性者TMZ化疗疗效较好。
联合IDH突变和MGMT甲基化两项分子标记物指标可以更好地指导sGBM的的诊治。
Part I:Clinical siginficance of IDH1and IDH2mutations in Chinese glioma patients
Background and Objective:
Gliomas are the most frequent and lethal tumors of the central nervous system(CNS) and show wide diversity with location, morphology, genetic status, and response to therapy. This group of tumors includes specific histologic subtypes, the most common of which are astrocytomas, oligodendrogliomas, and ependymomas. These tumors have been classified as grade I to grade IV based on histopathological and clinical criteria established by the World Health Organization (WHO). Despite intensive therapies, including surgery, radiotherapy, and chemotherapy, the outcome of glioma patients remains depressing. The median survival is only12to15months for patients with glioblastomas and2to5years for patients with anaplastic gliomas. Recently, there has been important progress in the treatment of malignant gliomas and in our understanding of the molecular pathogenesis of these tumors and the critical role that stem cells play in their development and resistance to treatment. As our understanding of the molecular correlates of response improves, it may be possible to select the most appropriate therapies on the basis of the patient's tumor genotype. These advances provide real opportunities for the development of effective therapies for malignant gliomas.
The latest breakthrough came in2008, when the genes encoding isocitrate dehydrogenase1(IDH1)(and to a lesser extent IDH2) were found to be mutated in lower grade gliomas and a subset of glioblastomas (those of the proneural type or having evolved from lower grade tumors). Interestingly, only1copy of the gene is mutated in the tumors, suggesting that the mutations do not result in a simple loss of function. The mutation is very specific and leads to a single amino acid change (arginine132usually becomes histidine) in the IDH1active site, whereby the enzyme loses its ability to catalyze conversion of isocitrate to a-ketoglutarate. Balss J et al. analyzed the genomic region spanning wild type R132of IDH1by direct sequencing in685brain tumors including41pilocytic astrocytomas,12subependymal giant cell astrocytomas,7pleomorphic xanthoastrocytomas,93diffuse astrocytomas,120adult glioblastomas,14pediatric glioblastomas,105oligodendrogliomas,83oligoastrocytomas,31ependymomas,58medulloblastomas,9supratentorial primitive neuroectodermal tumors,17schwannomas,72meningiomas and23pituitary adenomas. A total of221somatic IDH1mutations were detected and the highest frequencies occurred in diffuse astrocytomas (68%), oligodendrogliomas (69%), oligoastrocytomas (78%) and secondary glioblastomas (88%). Primary glioblastomas and other entities were characterized by a low frequency or absence of mutations in amino acid position132of IDH1. Yan H et al. determined the sequence of the IDH1gene and the related IDH2gene in445central nervous system (CNS) tumors and494non-CNS tumors, and identified mutations that affected amino acid132of IDH1in more than70%of WHO grade Ⅱand Ⅲastrocytomas and oligodendrogliomas and in glioblastomas that developed from these lower-grade lesions. Tumors without mutations in IDH1often had mutations affecting the analogous amino acid (R172) of the IDH2gene. Tumors with IDH1or IDH2mutations had distinctive genetic and clinical characteristics, and patients with such tumors had a better outcome than those with wild-type IDH genes. The impact of IDH1/2mutations on clinical outcome and the correlation between IDH1/2mutations and other molecular markers such as TP53mutations, EGFR amplification, MGMT promoter mthylation and BRAF fusion gene, had also been demonstrated in prospective clinical studies as well as in other various retrospective studies.
However, no report is currently available regarding the IDH1/2mutations in Chinese glioma patients and the predictive value of IDH mutations in patients treated with concomitant chemoradiotherapy following surgery. In the present study, we retrospectively analyzed a cohort of203Chinese glioma samples for IDH1/2mutations by high resolution melting (HRM) analysis combined with direct sequencing. This study aimed:i) to discern whether IDH mutations are common in Chinese glioma patients and ii) whether the mutations predict response to CCRT in anaplastic gliomas.
Methods and materials
This retrospective study was conducted by a single university hospital centre (Nanfang Gliomas Centre, Nanfang Hospital, Southern Medical University). All patients provided written informed consent for molecular studies of their tumor and the protocol was approved by the Ethics Committee of Nanfang Hospital. Clinical data were retrieved either from the case report forms for those patients participating in a clinical trial or from the hospital patient records. Clinical data included age, sex, location of tumors, pathological diagnosis, WHO performance scale(WHO-PS), date of final diagnosis, extent of surgery, adjuvant therapy after surgery (radiotherapy, chemotherapy), date of surgical resection, date of last follow-up or last contact, date of relapse, date of death and patient's status at this time. All patients who received concomitant chemoradiotherapy(CCRT) after surgery, took orally TMZ200mg/m2/d for5consecutive days of every28days(i.e. standard schedule) concurrent with radiotherapy(RT). In the absence of unacceptable toxicity or of disease progression, patients continued to receive TMZ for at least12cycles and up to30cycles or until progression. Formalin-fixed and paraffin-embedded archival tumour specimens were centralised at the Department of Pathology of Nanfang Hospital. After consensus pathological review by two independent neuropathologists, the tissue sections with the highest proportion of malignant cells was cut and sufficient for analysis of IDH mutations.
Statistical methods
All statistical analyses were done with SPSS13.0for Windows. All patients were evaluated by clinical examination and by gadolinium-enhanced magnetic resonance imaging (Gd-MRI) of the brain for every3months to6months. Responses of brain tumors are assessed using Macdonald criteria and disease progression is defined as greater than25%increase in T2hypersignal or contrast enhancement, or tumor-related neurologic deterioration apart from pseudoprogression and pseudoresponse that easily confuse the assessment of outcome. Frequency distribution and summary statistics were calculated for all clinical, histological, and molecular variables. The Chi-square test was used to assess the genotype distribution. The Independent-Samples T test was used to compare data acquired in each group for the patient age. Progression-free survival (PFS) and overall survival(OS)were both used to study the prognostic impact of the analyzed variables. Progression-free survival (PFS) was calculated from the start of the surgery until the first unequivocal clinical or radiologic sign of progressive disease or last follow-up (for censored cases). The overall survival was defined as the time between the first surgery and death or last follow-up (for censored cases). Survival distributions were estimated by Kaplan-Meier method and compared among patient subsets using log-rank tests. All statistical tests were two-sided, and the threshold for statistical significance was P=0.05. Patients who died within2weeks for HGG and2months for LGG after surgery were excluded from survival analyses to avoid the inclusion of cases in which death may have been attributable to surgical complications.
Results
IDH1mutations were present in75of the203cases (36.9%) while IDH2mutations in5of the203cases (2.5%). No tumor was mutated in both IDH1and IDH2. IDH1/2mutations were associated with prolonged overall survival in the whole series of patients exclusive of pilocytic astrocytoma (P﹤0.001), WHO grade II patients who received no adjuvant therapy after surgery(P=0.014), and WHO grade III patients who received concomitant chemoradiotherapy (standard schedule) after surgery(P=0.033). Furthermore, there was no correlation between IDH1/2 mutations and reponse to concomitant chemoradiotherapy in anaplastic gliomas.
Conclusion
Our results suggest that IDHl mutations also occur freuqently in Chinese glioma patients but the frequency of IDH1mutations is below the findings reported by North American and European groups. Furthermore, we confirm the prognostic significance of IDH1/2mutations in gliomas. but the mutations cannot predict a favorable response to concomitant chemoradiotherapy in anaplastic gliomas.
Part II:IDH mutations predict longer survival and response to temozolomide in secondary glioblastoma
Background and Objective:
Glioblastoma(GBM) is the most common malignant primary brain tumor in adults and among the most aggressive of all tumors, accounting for approximately50%of gliomas. The yearly incidence is3to5newly diagnosed cases per100.000population. Although glioblastoma occurs more frequently in the elderly (median age,64years), it may present at any age, but is rare in children. In younger patients, sec-ondary glioblastoma is more frequent (median age,45years). There is a slight preponderance of glioblastoma in males, with a male to female ratio of approximately1.3to1. The overall median progression-free and overall survival times for patients treated with the current standard chemoradiotherapy within large clinical trials are approximately7and15months, respectively. Glioblastoma is a diffusely growing malignant brain neoplasm with characteristic histological and imaging features. Most cases of glioblastoma (>90%, primary glioblastoma, pGBM) develop rapidly with a clinical history of only a few days or weeks (de novo). Some glioblastomas (10%) progress gradually from a lower grade glioma (grade Ⅱ or Ⅲ) and are also referred to as secondary glioblastoma(sGBM). Although molecularly distinct, primary and secondary glioblastoma are histologically indistinguishable. Recently, mutations of the IDH1and IDH2genes have been identified in>80%of all secondary glioblastoma cases.
In GBM the clinical value of O(6)-methylguanine DNA methyltransferase (MGMT) promotor methylation status in predicting benefit from alkylating agents has been validated by several clinical trials, both in patients treated with nitrosourea and in those with temozolomide (TMZ). In the European Organization for Research and Treatment of Cancer (EORTC)/National Cancer Institute of Canada (NCIC)26981/22981trial evaluating the effect of radiotherapy plus concomitant and adjuvant temozolomide versus radiotherapy alone in GBM, methylation of MGMT promotor methylation emerged as the strongest predictor for outcome and benefit from chemotherapy. However, all these studies were based on newly diagnosed GBMs, most of which were primary GBMs. So far there is no clear evidence that MGMT promotor methylation plays the same role in secondary GBMs since these two subtypes constitute distinct disease entities and develop through different genetic pathways. Similar to MGMT promotor methylation, patients with IDH1mutations are also associated with a longer survival than patients without in GBM. However, no data are currently available regarding the predictive value of IDH mutation in patients with secondary GBM treated with TMZ who have received surgery and radiotherapy due to a precursor lesion.
Therefore, in this study we investigated IDH mutation and MGMT promoter methylation in sGBM and their sensitivity to TMZ treatment.
Methods and materials
Search for IDH1and IDH2mutations,1p19q codeletion, O(6)-methylguanine DNA methyltransferase (MGMT) promoter methylation, and p53expression was performed in a series of86secondary glioblastomas and correlated with progression-free survival and overall survival. Response to temozolomide was evaluated by progression-free survival, as well as by tumor size on successive MR1scans, and then correlated with molecular alterations. The following inclusion criteria were selected:1) age18years or above at time of surgery;2) histologic diagnosis of sGBM (histologic evidence of a preceding low-grade glioma [LGG] or anaplastic glioma) according to the WHO classification[1].3) detailed clinical information at diagnosis and during follow-up;4) availability of tumor samples for molecular analysis;5) treated with TMZ in the period of January2003to December2009; and6) at least2cycles of TMZ after which time they were evaluated for response (clinical and Gd-MRI).
Statistical methods
All statistical analyses were done with SPSS13.0for Windows. The Chi-square test was used to test the association between molecular alterations and between radiologic response to chemotherapy and molecular alterations (Bonferroni test was used for multiple comparisons). The Independent-Samples T test was used to compare data for the patient age. Progression-free survival (PFS) and overall survival (OS) were both used to study the prognostic impact of the analyzed variables. PFS and OS were calculated from the date of the first day of TMZ administration until disease progression, death or last follow-up (for censored cases). Survival distributions were estimated by Kaplan-Meier method and compared among patient subsets using log-rank tests. Multivariate analysis was performed with the multivariate Cox proportional hazard regression model analysis. The significant variables in univariate analysis were included in the multivariate model:age (>55vs <55years), Karnofsky performance status (KPS)(>80vs≤80), IDH status and MGMT promoter status, as well as1p19q codeletion. All statistical tests were two-sided, and the threshold for statistical significance was p=0.05.
Results
IDH (IDH1or IDH2) mutations were found in58/79patients (73.4%). IDH mutation, MGMT promoter methylation, and1p19q codeletion were associated with prolonged progression-free survival in univariate (P<0.001, P<0.001, and P=0.003) and multivariate analysis (P<0.001, P<0.001and P=0.035). IDH mutation (P=0.001) and MGMT promoter methylation (P=0.011) were correlated with a higher rate of objective response to temozolomide. Further analysis of response to temozolomide showed that patients with both IDH mutation and MGMT promoter methylation had the best response rate to temozolomide.
Conclusion
IDH mutation appears to be a significant marker of positive chemosensitivity in secondary glioblastoma. Use of IDH status combined with MGMT promoter status as a stratification factor in future clinical trials involving temozolomide for the treatment of patients with secondary glioblastoma seems appropriate.
研究背景和目的
由星形细胞、少突胶质细胞、室管膜细胞等神经胶质细胞起源的胶质瘤是CNS最常见的恶性肿瘤,其生长部位、病理形态、基因遗传学改变和治疗效果有很大的差异性,通常依照其病理组织学类型分为低级别胶质瘤(WHO Ⅰ～Ⅱ级)和高级别胶质瘤(WHOⅢ～Ⅳ级)。胶质瘤呈浸润性生长,与正常脑组织界限不清,仅靠手术难以治愈,以最大程度上的手术切除为基础,结合放疗和化疗的综合治疗以延缓肿瘤复发和延长患者的生存期。尽管如此,WHOⅢ级胶质瘤者生存期一般才2-3年,而WHO Ⅳ级如胶质母细胞瘤(Glioblastoma,GBM)患者生存期仅为1年左右。胶质瘤患者的病死率居高不下,使其成为中枢神经系统(Central nervous system,CNS)最难攻克的肿瘤。令人庆幸的是,分子生物学的迅速发展给神经肿瘤学研究带来了一场深刻的变革,特别是胶质瘤的基础研究和临床研究的所有领域。随着人们对肿瘤的分子遗传学和表观遗传学认识不断提高,以及肿瘤分子流行病学、分子病理学等新兴学科的建立,CNS肿瘤发生、增殖、侵袭和血管形成的分子机制不断被揭示,同时也为开发各种分子靶向治疗药物提供了重要的理论基础。
最新的突破发生在2008年,Parsons等学者为了鉴定GBM的基因遗传学改变,对GBM的20661个蛋白的编码基因进行测序,在世界上首次发现了异柠檬酸脱氢酶1的编码基因(isocitrate dehydrogenase1, IDH1)突变存在于胶质瘤中。实验发现在149位GBM患者中有18位(12%)存在IDH1突变,且所有的IDH1突变都是发生在第四外显子的Arg132(R132)的氨基酸序列上,该项成果发表在当年的SCIENCE杂志上。Balss J等在685例包含了各种类型不同病理级别的胶质瘤中更大范围研究了IDH1的R132突变。IDⅢ突变在胶质瘤中频繁发生,其在弥漫性星形细胞瘤(WHO Ⅱ级)中发生率为68%,而在继发性GBM (Secondary glioblastoma, sGBM)中发生率达到88%。此外,少突胶质细胞瘤和少突胶质星形细胞瘤中的IDH1突变发生率分别为69%和78%,而在毛细胞性星形细胞瘤(WHO Ⅰ级)中没有检测到IDH1/2突变。2009年新英格兰杂志上发表了美国杜克大学HaiYan等的文章,研究者们在445个CNS肿瘤和494个非CNS肿瘤中进行了IDH1和IDH2的基因突变检测,发现IDH1突变不仅仅存在于WHOⅣ级GBM中,也广泛存在于WHO Ⅱ级、Ⅲ级的星形细胞瘤和少突胶质细胞瘤中。在445个CNS肿瘤样本中检测到了161个IDH1的R132突变,在毛细胞性星形细胞瘤、室管膜下巨细胞瘤(WHO Ⅰ级)、室管膜瘤(WHO Ⅱ级)、髓母细胞瘤及其他非CNS肿瘤中均没有检测到IDH1突变。随后胶质瘤相关的IDH突变被的其他中心的一些学者相继研究证实,揭示了IDH1/2突变与患者的年龄,病理类型以及临床预后的关系,并且发现IDH突变与其他胶质瘤分子标记物比如TP53突变,表皮生长因子受体基因(Epithelial growth factor receptor gene, EGFR)扩增,BRAF fusion基因,1p19q杂合性缺损以及O6-甲基鸟嘌呤-DNA甲基转移酶(O(6)-methylguanine DNA methyltransferase, MGMT)启动子甲基化都有一定的相关性。
但是在本实验完成之前尚未有针对中国人群中胶质瘤患者的IDH突变的相关报道。那么,在中国人群胶质瘤患者中是否同样存在IDH突变?其发生率与欧美国家的研究结果是否有差异?IDH突变与胶质瘤患者同步放化疗(Concomitant chemoradiotherapy, CCRT)的疗效有没有关联?本研究旨在通过聚合酶链反应—高分辨率熔解分析方法和直接测序的方法检测中国人群胶质瘤患者IDH突变情况,并与国外文献报道的结果进行比较。另外本研究也初步探讨了IDH突变与胶质瘤患者CCRT效果的关系。
方法
研究对象
收集南方医科大学南方医院神经外科203例中国人群胶质瘤患者的肿瘤标本(包括各个WHO级别和不同的病理类型),所有的肿瘤标本都取自本院病理科的石蜡包埋组织,而患者的临床资料来自南方医院电子病历系统的病历记录。所有肿瘤标本均先经两位以上病理科医生进行病理确认,取含有肿瘤细胞最多的部分组织做切片。患者的临床资料包括年龄、性别、病理诊断、健康状况评分(WHO-performance scale, WHO-PS)、手术切除程度、术后辅助治疗情况(放疗、化疗或者CCRT)、确诊日期、手术日期、复发日期、死亡日期、最后一次随访日期以及最后一次随访时患者的生存状态。术后CCRT的方案是国际上的标准方案即Stupp方案：放疗的整个疗程应同步化疗,口服替莫唑胺(Temozolomide, TMZ)75mg/m2,疗程42d。放疗结束后2-4周,辅助TMZ治疗150mg/m2,连续用药5天,28d为一个疗程,若耐受良好,则在以后化疗疗程中增量至200mg/m2,推荐辅助TMZ化疗6-12个疗程。采用聚合酶链反应—高分辨率熔解分析方法及直接测序法检测IDH1和IDH2突变情况,研究IDH突变与患者临床预后之间的关系。
统计学处理
所有统计学计算均使用SPSS13.0软件完成。计数资料采用卡方检验进行差异性检验,独立样本T检验用来分析IDH突变阳性组和IDH突变阴性组的年龄差别。无进展生存期(Progression-free survival, PFS)和总体生存期(Overall survival, OS)用来反映患者的预后情况。PFS和OS用来反映患者的临床预后,两者均以手术当天为第一天开始计算,前者到患者病情进展确诊的当天结束,后者到患者死亡当天或者最后一次随访结束(删失数据)。应用Kaplan-Meier法行生存分析、Log-rank法行显著性检验以比较不同患者的生存差异,以P<0.05为差异有统计学意义。需要注意的是,高级别胶质瘤患者术后2周之内死亡或者低级别胶质瘤患者术后2月之内死亡不纳入生存分析中,因为其死亡可能是手术的并发症所致,不是疾病的自然进程。
结果
203例胶质瘤患者中(包括WHO Ⅰ级5例：毛细胞型星形细胞瘤5例；WHOⅡ级86例：节细胞胶质瘤4例,弥漫性星形细胞瘤60例,少突胶质细胞瘤8例,少突胶质星形细胞瘤14例；WHOⅢ级67例：间变性星形细胞瘤49例,间变性少突胶质星形细胞瘤11例,间变性少突胶质细胞瘤7例；WHOIV级45例：pGBM38例,sGBM7例)有80例存在IDH突变,其中IDH1突变75例(36.9%)、IDH2突变5例(2.5%)。没有一例样本同时存在IDH1和IDH2两种突变。IDH突变型患者较IDH野生型患者年龄更年轻,手术的全切率更高。分组讨论中(主要分为：除外WHO Ⅰ级毛细胞型星形细胞瘤的整体组,WHOⅡ级无术后辅助治疗亚组,WHOⅢ级术后行CCRT亚组),无论是在除外5例WHO Ⅰ级患者的总体上比较(P<0.001),还是在WHO Ⅱ级无术后辅助治疗的患者组(P=0.014)以及在WHOⅢ级术后行CCRT组内(P=0.033)比较,IDH突变阳性患者的OS比IDH突变阴性患者的OS长。另外在WHOⅢ级术后行CCRT组,IDH突变与CCRT疗效无相关性。
结论
IDH突变同样广泛存在于中国人群胶质瘤患者中(WHOⅡ～Ⅲ级的胶质瘤以及WHOⅣ级的sGBM),但IDH1突变率却稍低于欧美国家研究中心的报道,IDH1/2的突变类型也少于以往国外的报道。本组数据也再次证实了IDH突变型患者预后相对IDH野生型患者较好,但是IDH突变在间变性胶质瘤中与患者术后CCRT的疗效无相关性。
第二部分：异柠檬酸脱氢酶基因突变在继发性胶质母细胞瘤中与替莫唑胺疗效的关系
研究背景和目的
GBM是成年人中最常见、恶性程度最高的脑肿瘤,也是恶性胶质瘤中最常见的类型(约一半以上),其年发病率约3-5/10万人,可发生在任何年龄段,最常发生在老年人(年龄的中位数为64岁,sGBM患者发病年龄要稍年轻,年龄的中位数为45岁),很少发生在儿童患者。GBM具有很高的致残和致死率,严重威胁人类健康,而其治疗前景至今仍然不容乐观。即使经过最大程度上的手术切除和术后规范的CCRT, GBM患者的中位PFS和OS也仅仅只有7个月和15个月。GBM呈浸润性生长,具有特征性的病理组织学特点和影像学特点。90%以上的GBM是原发性的(Primary Glioblastoma multiforme, pGBM),进展很快,病程从几天到几周不等。约10%的GBM是继发性的,是由WHO Ⅱ或Ⅲ级胶质瘤逐渐进展而来。pGBM和sGBM虽然在病理组织学上很难区分,但是两者具有截然不同的分子生物学转导通路。近几年来越来越多的研究结果表明IDH1和IDH2突变广泛存在于sGBM中。
在GBM中MGMT启动子甲基化不仅仅是患者临床预后的良性指标,更是预测TMZ疗效的敏感指标。而在间变性胶质瘤中,MGMT启动子甲基化仅仅是一个良性预后指标,与TMZ的疗效无关。事实上MGMT启动子甲基化作为预测TMZ疗效的敏感指标主要是针对于新诊断的GBM,而新诊断的GBM中约90%是原发性,继发性的只占到10%左右。然而如前所述,pGBM和sGBM虽然在病理组织学上很难区分,但是两者发病的分子生物学机制截然不同,因此很难说MGMT启动子甲基化在sGBM中扮演着同样的角色。另外在sGBM中,MGMT启动子甲基化往往和IDH1/2突变同时存在,而H1/2也是胶质瘤患预后的强有力的预测指标,那么在sGBM患者临床预后方面,MGMT启动子甲基化与IDH1/2的关系如何?孰轻孰重?还有在sGBM患者中,在TMZ疗效方面,MGMT启动子甲基化与IDH1/2的关系又如何?我们查阅国内外文献,尚没有这方面的报道。本研究目的是探讨IDH突变对sGBM患者TMZ化疗临床预后的影响,以及与其他分子标记物如p53表达、MGMT启动子甲基化、1p19q杂合性缺失的关系。
方法
研究对象
收集2003年1月至2009年12月经手术证实的sGBM86例,分别检测IDH1/2突变、1p19q杂合性缺失、MGMT启动子甲基化和p53表达,利用生存分析比较这些指标与患者临床预后(即PFS和OS)的关系。反映TMZ疗效的主要指标是用药后的患者PFS和肿瘤大小(通过定期的头颅磁共振检查来反映)。
统计学处理
各项分子标记物指标之间的相关性以及各项分子标记物指标与TMZ疗效(主要是通过影像学上的改变来反映)的关系用卡方检验(其中多重比较用Bonferroni检测法)。独立样本T检验用来分析IDH突变阳性组和IDH突变阴性组的年龄差别。PFS和OS用来反映患者的临床预后,两者均从使用TMZ的第一天开始计算,前者到患者病情进展确诊的当天结束,后者到患者死亡当天或者最后一次随访结束(删失数据)。应用Kaplan-Meier法行生存分析、Log-rank法行显著性检验以比较不同患者的生存差异。进行多变量分析以了解各因素对生存期的影响,本研究中使用Cox比例风险回归模型来估计风险比(HR),并计算95%可信区间(CI)和P值,运用逐步回归法进行各因素的筛选及最优模型的建立。以上统计学方法均采用双尾检验,检验水准α取0.05,数据的分析均采用SPSS13.0版本。
结果
79例患者中有58例存在IDH1或者IDH2突变(突变率73.4%,7例肿瘤样本无法检测)。IDH突变、MGMT启动子甲基化以及1p19q杂合性缺失均与患者的PFS呈正相关。IDH突变阳性或者MGMT启动子甲基化的患者对TMZ的疗效更好,主要反映在相同的时间内肿瘤体积的缩小更明显。IDH突变阳性和MGMT甲基化同时存在的患者,TMZ治疗的效果最好。
结论
本研究通过对86例sGBM的各项分子标记物指标检测,结合随访以及系统的生存分析得出以下结论：
IDH突变是sGBM TMZ化疗疗效的一个有效的预测指标,即IDH突变阳性者TMZ化疗疗效较好。
联合IDH突变和MGMT甲基化两项分子标记物指标可以更好地指导sGBM的的诊治。
Part I:Clinical siginficance of IDH1and IDH2mutations in Chinese glioma patients
Background and Objective:
Gliomas are the most frequent and lethal tumors of the central nervous system(CNS) and show wide diversity with location, morphology, genetic status, and response to therapy. This group of tumors includes specific histologic subtypes, the most common of which are astrocytomas, oligodendrogliomas, and ependymomas. These tumors have been classified as grade I to grade IV based on histopathological and clinical criteria established by the World Health Organization (WHO). Despite intensive therapies, including surgery, radiotherapy, and chemotherapy, the outcome of glioma patients remains depressing. The median survival is only12to15months for patients with glioblastomas and2to5years for patients with anaplastic gliomas. Recently, there has been important progress in the treatment of malignant gliomas and in our understanding of the molecular pathogenesis of these tumors and the critical role that stem cells play in their development and resistance to treatment. As our understanding of the molecular correlates of response improves, it may be possible to select the most appropriate therapies on the basis of the patient's tumor genotype. These advances provide real opportunities for the development of effective therapies for malignant gliomas.
The latest breakthrough came in2008, when the genes encoding isocitrate dehydrogenase1(IDH1)(and to a lesser extent IDH2) were found to be mutated in lower grade gliomas and a subset of glioblastomas (those of the proneural type or having evolved from lower grade tumors). Interestingly, only1copy of the gene is mutated in the tumors, suggesting that the mutations do not result in a simple loss of function. The mutation is very specific and leads to a single amino acid change (arginine132usually becomes histidine) in the IDH1active site, whereby the enzyme loses its ability to catalyze conversion of isocitrate to a-ketoglutarate. Balss J et al. analyzed the genomic region spanning wild type R132of IDH1by direct sequencing in685brain tumors including41pilocytic astrocytomas,12subependymal giant cell astrocytomas,7pleomorphic xanthoastrocytomas,93diffuse astrocytomas,120adult glioblastomas,14pediatric glioblastomas,105oligodendrogliomas,83oligoastrocytomas,31ependymomas,58medulloblastomas,9supratentorial primitive neuroectodermal tumors,17schwannomas,72meningiomas and23pituitary adenomas. A total of221somatic IDH1mutations were detected and the highest frequencies occurred in diffuse astrocytomas (68%), oligodendrogliomas (69%), oligoastrocytomas (78%) and secondary glioblastomas (88%). Primary glioblastomas and other entities were characterized by a low frequency or absence of mutations in amino acid position132of IDH1. Yan H et al. determined the sequence of the IDH1gene and the related IDH2gene in445central nervous system (CNS) tumors and494non-CNS tumors, and identified mutations that affected amino acid132of IDH1in more than70%of WHO grade Ⅱand Ⅲastrocytomas and oligodendrogliomas and in glioblastomas that developed from these lower-grade lesions. Tumors without mutations in IDH1often had mutations affecting the analogous amino acid (R172) of the IDH2gene. Tumors with IDH1or IDH2mutations had distinctive genetic and clinical characteristics, and patients with such tumors had a better outcome than those with wild-type IDH genes. The impact of IDH1/2mutations on clinical outcome and the correlation between IDH1/2mutations and other molecular markers such as TP53mutations, EGFR amplification, MGMT promoter mthylation and BRAF fusion gene, had also been demonstrated in prospective clinical studies as well as in other various retrospective studies.
However, no report is currently available regarding the IDH1/2mutations in Chinese glioma patients and the predictive value of IDH mutations in patients treated with concomitant chemoradiotherapy following surgery. In the present study, we retrospectively analyzed a cohort of203Chinese glioma samples for IDH1/2mutations by high resolution melting (HRM) analysis combined with direct sequencing. This study aimed:i) to discern whether IDH mutations are common in Chinese glioma patients and ii) whether the mutations predict response to CCRT in anaplastic gliomas.
Methods and materials
This retrospective study was conducted by a single university hospital centre (Nanfang Gliomas Centre, Nanfang Hospital, Southern Medical University). All patients provided written informed consent for molecular studies of their tumor and the protocol was approved by the Ethics Committee of Nanfang Hospital. Clinical data were retrieved either from the case report forms for those patients participating in a clinical trial or from the hospital patient records. Clinical data included age, sex, location of tumors, pathological diagnosis, WHO performance scale(WHO-PS), date of final diagnosis, extent of surgery, adjuvant therapy after surgery (radiotherapy, chemotherapy), date of surgical resection, date of last follow-up or last contact, date of relapse, date of death and patient's status at this time. All patients who received concomitant chemoradiotherapy(CCRT) after surgery, took orally TMZ200mg/m2/d for5consecutive days of every28days(i.e. standard schedule) concurrent with radiotherapy(RT). In the absence of unacceptable toxicity or of disease progression, patients continued to receive TMZ for at least12cycles and up to30cycles or until progression. Formalin-fixed and paraffin-embedded archival tumour specimens were centralised at the Department of Pathology of Nanfang Hospital. After consensus pathological review by two independent neuropathologists, the tissue sections with the highest proportion of malignant cells was cut and sufficient for analysis of IDH mutations.
Statistical methods
All statistical analyses were done with SPSS13.0for Windows. All patients were evaluated by clinical examination and by gadolinium-enhanced magnetic resonance imaging (Gd-MRI) of the brain for every3months to6months. Responses of brain tumors are assessed using Macdonald criteria and disease progression is defined as greater than25%increase in T2hypersignal or contrast enhancement, or tumor-related neurologic deterioration apart from pseudoprogression and pseudoresponse that easily confuse the assessment of outcome. Frequency distribution and summary statistics were calculated for all clinical, histological, and molecular variables. The Chi-square test was used to assess the genotype distribution. The Independent-Samples T test was used to compare data acquired in each group for the patient age. Progression-free survival (PFS) and overall survival(OS)were both used to study the prognostic impact of the analyzed variables. Progression-free survival (PFS) was calculated from the start of the surgery until the first unequivocal clinical or radiologic sign of progressive disease or last follow-up (for censored cases). The overall survival was defined as the time between the first surgery and death or last follow-up (for censored cases). Survival distributions were estimated by Kaplan-Meier method and compared among patient subsets using log-rank tests. All statistical tests were two-sided, and the threshold for statistical significance was P=0.05. Patients who died within2weeks for HGG and2months for LGG after surgery were excluded from survival analyses to avoid the inclusion of cases in which death may have been attributable to surgical complications.
Results
IDH1mutations were present in75of the203cases (36.9%) while IDH2mutations in5of the203cases (2.5%). No tumor was mutated in both IDH1and IDH2. IDH1/2mutations were associated with prolonged overall survival in the whole series of patients exclusive of pilocytic astrocytoma (P﹤0.001), WHO grade II patients who received no adjuvant therapy after surgery(P=0.014), and WHO grade III patients who received concomitant chemoradiotherapy (standard schedule) after surgery(P=0.033). Furthermore, there was no correlation between IDH1/2 mutations and reponse to concomitant chemoradiotherapy in anaplastic gliomas.
Conclusion
Our results suggest that IDHl mutations also occur freuqently in Chinese glioma patients but the frequency of IDH1mutations is below the findings reported by North American and European groups. Furthermore, we confirm the prognostic significance of IDH1/2mutations in gliomas. but the mutations cannot predict a favorable response to concomitant chemoradiotherapy in anaplastic gliomas.
Part II:IDH mutations predict longer survival and response to temozolomide in secondary glioblastoma
Background and Objective:
Glioblastoma(GBM) is the most common malignant primary brain tumor in adults and among the most aggressive of all tumors, accounting for approximately50%of gliomas. The yearly incidence is3to5newly diagnosed cases per100.000population. Although glioblastoma occurs more frequently in the elderly (median age,64years), it may present at any age, but is rare in children. In younger patients, sec-ondary glioblastoma is more frequent (median age,45years). There is a slight preponderance of glioblastoma in males, with a male to female ratio of approximately1.3to1. The overall median progression-free and overall survival times for patients treated with the current standard chemoradiotherapy within large clinical trials are approximately7and15months, respectively. Glioblastoma is a diffusely growing malignant brain neoplasm with characteristic histological and imaging features. Most cases of glioblastoma (>90%, primary glioblastoma, pGBM) develop rapidly with a clinical history of only a few days or weeks (de novo). Some glioblastomas (10%) progress gradually from a lower grade glioma (grade Ⅱ or Ⅲ) and are also referred to as secondary glioblastoma(sGBM). Although molecularly distinct, primary and secondary glioblastoma are histologically indistinguishable. Recently, mutations of the IDH1and IDH2genes have been identified in>80%of all secondary glioblastoma cases.
In GBM the clinical value of O(6)-methylguanine DNA methyltransferase (MGMT) promotor methylation status in predicting benefit from alkylating agents has been validated by several clinical trials, both in patients treated with nitrosourea and in those with temozolomide (TMZ). In the European Organization for Research and Treatment of Cancer (EORTC)/National Cancer Institute of Canada (NCIC)26981/22981trial evaluating the effect of radiotherapy plus concomitant and adjuvant temozolomide versus radiotherapy alone in GBM, methylation of MGMT promotor methylation emerged as the strongest predictor for outcome and benefit from chemotherapy. However, all these studies were based on newly diagnosed GBMs, most of which were primary GBMs. So far there is no clear evidence that MGMT promotor methylation plays the same role in secondary GBMs since these two subtypes constitute distinct disease entities and develop through different genetic pathways. Similar to MGMT promotor methylation, patients with IDH1mutations are also associated with a longer survival than patients without in GBM. However, no data are currently available regarding the predictive value of IDH mutation in patients with secondary GBM treated with TMZ who have received surgery and radiotherapy due to a precursor lesion.
Therefore, in this study we investigated IDH mutation and MGMT promoter methylation in sGBM and their sensitivity to TMZ treatment.
Methods and materials
Search for IDH1and IDH2mutations,1p19q codeletion, O(6)-methylguanine DNA methyltransferase (MGMT) promoter methylation, and p53expression was performed in a series of86secondary glioblastomas and correlated with progression-free survival and overall survival. Response to temozolomide was evaluated by progression-free survival, as well as by tumor size on successive MR1scans, and then correlated with molecular alterations. The following inclusion criteria were selected:1) age18years or above at time of surgery;2) histologic diagnosis of sGBM (histologic evidence of a preceding low-grade glioma [LGG] or anaplastic glioma) according to the WHO classification[1].3) detailed clinical information at diagnosis and during follow-up;4) availability of tumor samples for molecular analysis;5) treated with TMZ in the period of January2003to December2009; and6) at least2cycles of TMZ after which time they were evaluated for response (clinical and Gd-MRI).
Statistical methods
All statistical analyses were done with SPSS13.0for Windows. The Chi-square test was used to test the association between molecular alterations and between radiologic response to chemotherapy and molecular alterations (Bonferroni test was used for multiple comparisons). The Independent-Samples T test was used to compare data for the patient age. Progression-free survival (PFS) and overall survival (OS) were both used to study the prognostic impact of the analyzed variables. PFS and OS were calculated from the date of the first day of TMZ administration until disease progression, death or last follow-up (for censored cases). Survival distributions were estimated by Kaplan-Meier method and compared among patient subsets using log-rank tests. Multivariate analysis was performed with the multivariate Cox proportional hazard regression model analysis. The significant variables in univariate analysis were included in the multivariate model:age (>55vs <55years), Karnofsky performance status (KPS)(>80vs≤80), IDH status and MGMT promoter status, as well as1p19q codeletion. All statistical tests were two-sided, and the threshold for statistical significance was p=0.05.
Results
IDH (IDH1or IDH2) mutations were found in58/79patients (73.4%). IDH mutation, MGMT promoter methylation, and1p19q codeletion were associated with prolonged progression-free survival in univariate (P<0.001, P<0.001, and P=0.003) and multivariate analysis (P<0.001, P<0.001and P=0.035). IDH mutation (P=0.001) and MGMT promoter methylation (P=0.011) were correlated with a higher rate of objective response to temozolomide. Further analysis of response to temozolomide showed that patients with both IDH mutation and MGMT promoter methylation had the best response rate to temozolomide.
Conclusion
IDH mutation appears to be a significant marker of positive chemosensitivity in secondary glioblastoma. Use of IDH status combined with MGMT promoter status as a stratification factor in future clinical trials involving temozolomide for the treatment of patients with secondary glioblastoma seems appropriate.
引文
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