A Prospective Cohort to Study the Effect of Temozolomide on IDH Mutational Low Grade Gliomas

Overview

Low grade gliomas (LGGs) are the most common primary central nervous system malignancies. Brain surgeries with the most possible extent of resection are endeavored to achieve longer survivals in LGG patients. For patients with tumor located in eloquent areas so that gross total resection is not applicable, National Comprehensive Cancer Network (NCCN) 2013 guidelines assigned both radiotherapy or chemotherapy as adjuvant treatments of low grade glioma following surgeries. Retrospective studies have suggested that temozolomide (an oral chemotherapeutics) chemotherapy have good effects on the control of tumor progression or recurrence in LGG patients after surgeries, especially in those with isocitrate dehydrogenase (IDH) gene mutations. Therefore, our prospective cohort study is to provide a higher level(IIb) of evidence for the correlation between IDH mutation and the responsiveness to up-front adjuvant metronomic temozolomide chemotherapy in young patients with LGG located in eloquent brain areas. And hopefully justify future RCTs with comparison between effects of adjuvant radiotherapy and chemotherapy in these patients.

Low grade gliomas, according to the 2007 WHO classification of tumors of the central nervous system, include astrocytomas, oligodendrogliomas, and oligoastrocytomas. It contributes to 25% of diffuse gliomas and 15% of all gliomas in adults. The majority of age group that is the most vulnerable to this neoplasm is from 30-45 years old. Median survival is usually 5-12 years, but can be prolonged up to 20 years under optimal treatment strategies. National Comprehensive Cancer Network (NCCN) and Chinese Guideline for Gliomas 2012 both point out that for LGG patients in low-risk group (oligodendrogliomas or oligoastrocytomas; no more than 40 years old; KPS 80 and higher; tumor size less than 6cm; no or minor neurological deficits), "wait and see" strategy could be considered after gross total resection; but when the tumors are in eloquent areas so that gross total resections are not applicable, the standard strategies for this specific group of patients are maximum safely resection with adjuvant treatments (radiotherapy and/or chemotherapy). Conventionally, radiotherapy is used as adjuvant treatment after surgeries. However, a recent phase III randomized trial comparing early versus later irradiation has demonstrated that early adjuvant radiotherapy had no significant impact on overall survival. Moreover, radiotherapy brings as much side effects as its control of tumor recurrence. It inevitably jeopardizes patients, especially young ones, with post-radiation cognitive deficits, which impair their social functions. On the other hand, chemotherapy could be a safer adjuvant treatment for LGG. Several phase II and III studies demonstrated that single chemotherapy is effective for treating LGG, with 50-75% response rate (including minor response), and 24-48 months of median duration of response.PCV regimen (procarbazine-CCNU-vincristine), which is administrated intravenously, used to be considered standard for LGG (oligodendrogliomas and oligoastrocytomas) chemotherapy, but now temozolomide (TMZ), an oral alkylating agent, with relatively less side effects than PCV regimen, is gaining gradual acceptance. Now we propose up-front adjuvant chemotherapy to achieve the effect of early tumor control as well as avoidance or postponement of adverse effects caused by premature adjuvant radiotherapy. As for different schedules of temozolomide, a systematic review suggested an indication that metronomic regimens of TMZ (75 mg/m2/day for 21 days repeated every 4 weeks) result in better PFS and response rate when compared to the conventional standard 5 day regimen (200 mg/m2/day for 5 days, repeated every 4 weeks), despite of insufficient available data and study heterogeneity, thus justifying future well designed trials to verify the efficacy of the metronomic regimen. More frequent administration of TMZ will lead to MGMT (O6-methylguanine DNA methyl transferase) depletion and render higher levels of O6-methylated DNA adducts, thus reducing the chemotherapeutic resistance. The spontaneous behavior of LGGs, as well as their response to therapy, is difficult to predict, and their outcome is highly variable. These clinical features are closely relevant to their genetic characteristics, including IDH (isocitrate dehydrogenase) gene, with 2 subtypes, IDH1 and IDH2 (less common). These genetic mutations occur in more than 70% primary LGGs. And its prognostic significance of gliomas has been reported in the New England Journal of Medicine, Journal of Clinical Oncology, and Neuro-oncology. A retrospective study suggested its predictive value of high LGGs sensitivity to TMZ. Basic research provided us the rationale that overexpression of wild IDH1 gene resulted in chemotherapy resistance to a high dose of TMZ in vivo and in vitro, while IDH1 mutation caused cell cycle arrest in G1 stage, with a compromised ability of proliferation and invasion, raising sensitivity to chemotherapy. During our previous clinical practice, it is interesting to reveal the consistence of IDH mutation, MGMT methylation and 1p19q co-deletion in WHO Grade II and Grade III gliomas. It theoretically acknowledged potential higher sensitivity of TMZ chemotherapy in LGGs. In order to verify the predictive significance of IDH mutation for a higher sensitivity of LGGs in eloquent areas which entail gross total resection inapplicable, higher level of evidence should be provided. And recent RANO (response assessment in neuro-oncology) revised guidelines for evaluations of objective response rate, cognitive functions, and quality of life have better facilitated standard trials.