Comparison Of Genetic Characteristics In Paired Primary And Recurrent Glioma

ObjectivesGlioma is prone to recurrence.Despite radical radiotherapy and chemotherapy after total resection,recurrence is inevitable.Since glioma cells growth infiltratively,they are hard to eliminate absolutely by sugery.Part of residue glioma cells are resistant to radiation and chemotherapeutic agents,which become the source of recurrence.The mechanism of resistance is not very clear.There are many hypothesis including cancer stem cells,hypoxia and so on.The recurrent gliomas are more invasive,they grow more quikly,and have less response to therapy.The treatment of recurrent glioma is always a problem bothers clinicians.Temozolomide(TMZ),a kind of alkylating agent,is the standard chemotherapeutic agent for the treatment of glioma.But its role in recurrent glioma is not significant.Bevacizumab,a kind of anti-angiogenesis agent,can prolong glioma patients’ PFS.Howerver,it can’t prolong OS.Recently,immunotherapy has shown promising therapeutic effect in other solid tumors,but they are still in clinical trail on the treatment of recurrent glioma.Therefore,it is crucial to know the potential factors that relate to recurrence and malignant transformation of glioma.Our study tries to analysis the genetic characteristics in paired primary and recurrent glioma,aims to know more about the biological behaviour of glioma and the difference of genetic characteristics of primary and recurrent gliomas,and eventually rich our kownledge of glioma.MethodsPatients with glioma who had undergone surgery for the primary tumor in the brain at our institution from January 2013 to December 2015 were retrospectively analyzed.50 recurrent patients who undergone a second recection were included.MGMT promotor methylation status was determined for these patients by pyrosequencing analysis.The protein expression of the immune checkpoint gene(PD-1 and PD-L1),angiogenesis gene(VEGF,VEGFR2 and HIF-1α),stem cell related gene(CD133,EZH2 and SOX2)and MGMT was tested by immunohistochemistry.ResultsThe protein expression level of PD-1,PD-L1,VEGF,VEGFR2,CD 133 and MGMT was increased in recurrent glioma compared to the paied primary sample.And the MGMT promotor methylation status tended to change from methylated to unmethylated.While the protein expression level of SOX2 was decreased.The protein expression of PD-1,VEGF,VEGFR2,CD 133 and EZH2 was correlated significantly with glioma’s WHO grade.There was a positive correlation between PD-1 and PD-L1,VEGF and VEGFR2,CD133 and EZH2,respectively.Patients who had protein expression of VEGF in primary sample had significantly shorter medium progression-free survival(PFS)than those without VEGF protein expression(12.5 vs 17 months,p=0.031).Patients who had coexpression of VEGF and VEGFR2 in primary sample had shortest medium PFS than those only express one protein,and those express none of this two gene had longest medium PFS(11.2 vs 12.7 vs 18 months,p=0.046).Patients who had high expression of CD 133 in primary sample had significantly shorter medium PFS than those with low expression(12.5 vs 25.2 months,p=0.015).Patients who had high expression of EZH2 in primary sample also had significantly shorter medium PFS than those with low expression(10.3 vs 17.0 months,p=0.003).While patients who had high expression of SOX2 in primary sample had significantly longer medium progression-free survival(PFS)than those with low expression(51.1 vs 20.9 months,p=0.001).Conclutions and significance for theory and practiceTo our knowledge,this study systematically compared the protein expression of the immune checkpoint gene(PD-1 and PD-L1),angiogenesis gene(VEGF,VEGFR2 and HIF-1α),stem cell related gene(CD133,EZH2 and SOX2)and epigenetic modification gene MGMT and the promotor methylation status of MGMT in the primary and paired recurrent glioma samples for the first time.Compared with the primay gliomas,the recurrent tumors have more disordered immunity,more angiogenisis and more stem cells.And the MGMT promor methylation status turns to unmethylated.So the biological behavior of the recurrent glioma is more malignant and it has less response to therapy.TMZ is the most important chemotherapeutic agent in the therapy of glioma.However,in our study,we found MGMT promotor methylation status tended to decrease and the protein expression of MGMT increased in recurrent gliomas compared with the primary samples.Therefore,recurrent glioma may be less sensitive to TMZ.Exploring new chemotherapeutic agent is necessary in the future.Bevacizumab is the second important chemotherapeutic agent in glioma.Several clinical trails have demonstrated that it can prolong PFS of patients with glioblastoma,but it didn’t prolong OS.Our study find that the expression of VEGF,which is the target of bevacizumab,increased in recurrent glioma compared with the primary sample.So bevacizumab may have potentail value in the treatment of recurrent glioma.While the expression of another angiogenesis gene VEGFR2 and immune checkpoint gene PD-land PD-L1 also increased.At the same time,glioma stem cells accrued as well.Therefore,patients with recurrent giloma may benefit from the combination of chemotherapeutic agents targeting various signal pathways such angiogenesis,immune checkpoint and stem cells.