Plasma ctDNA liquid biopsy of IDH1, TERTp, and EGFRvIII mutations in glioma.

Background: Circulating tumor DNA has emerging clinical applications in several cancers; however, previous studies have shown low sensitivity in glioma. We investigated if 3 key glioma gene mutations IDH1, TERTp, and EGFRvIII could be reliably detected in plasma by droplet digital polymerase chain reaction (ddPCR) thereby demonstrating the potential of this technique for glioma liquid biopsy. Methods: We analyzed 110 glioma patients from our biobank with a total of 359 plasma samples (median 4 samples per patient). DNA was isolated from plasma and analyzed for IDH1, TERTp, and EGFRvIII mutations using ddPCR. Results: Total cfDNA was significantly associated with tumor grade, tumor volume, and both overall and progression-free survival for all gliomas as well as the grade 4 glioblastoma subgroup, but was not reliably associated with changes in tumor volume/progression during the patients' postoperative time course. IDH1 mutation was detected with 84% overall sensitivity across all plasma samples and 77% in the preoperative samples alone; however, IDH1 mutation plasma levels were not associated with tumor progression or survival. IDH1m plasma levels were not associated with pre- or postsurgery progression or survival. The TERTp C228T mutation was detected in the plasma ctDNA in 88% but the C250T variant in only 49% of samples. The EGFRvIII mutation was detected in plasma in 5 out of 7 patients (71%) with tissue EGFRvIII mutations in tumor tissue. Conclusions: Plasma ctDNA mutations detected with ddPCR provide excellent diagnostic sensitivity for IDH1, TERTp-C228T, and EGFRvIII mutations in glioma patients. Total cfDNA may also assist with prognostic information. Further studies are needed to validate these findings and the clinical role of ctDNA in glioma.

Plasma ctDNA enables early detection of temozolomide resistance mutations in glioma.

Background: Liquid biopsy based on circulating tumor DNA (ctDNA) is a novel tool in clinical oncology, however, its use has been limited in glioma to date, due to low levels of ctDNA. In this study, we aimed to demonstrate that sequencing techniques optimized for liquid biopsy in glioma patients can detect ctDNA in plasma with high sensitivity and with potential clinical utility. Methods: We investigated 10 glioma patients with tumor tissue available from at least 2 surgical operations, who had 49 longitudinally collected plasma samples available for analysis. Plasma samples were sequenced with CAPP-seq (AVENIO) and tissue samples with TSO500. Results: Glioma-derived ctDNA mutations were detected in 93.8% of plasma samples. 25% of all mutations detected were observed in plasma only. Mutations of the mismatch repair (MMR) genes MSH2 and MSH6 were the most frequent circulating gene alterations seen after temozolomide treatment and were frequently observed to appear in plasma prior to their appearance in tumor tissue at the time of surgery for recurrence. Conclusions: This pilot study suggests that plasma ctDNA in glioma is feasible and may provide sensitive and complementary information to tissue biopsy. Furthermore, plasma ctDNA detection of new MMR gene mutations not present in the initial tissue biopsy may provide an early indication of the development of chemotherapy resistance. Additional clinical validation in larger cohorts is needed.

A Phase II trial of alternating osimertinib and gefitinib therapy in advanced EGFR-T790M positive non-small cell lung cancer: OSCILLATE.

In this phase II, single arm trial (ACTRN12617000720314), we investigate if alternating osimertinib and gefitinib would delay the development of resistance to osimertinib in advanced, non-small cell lung cancer (NSCLC) with the epidermal growth factor receptor (EGFR) T790M mutation (n = 47) by modulating selective pressure on resistant clones. The primary endpoint is progression free-survival (PFS) rate at 12 months, and secondary endpoints include: feasibility of alternating therapy, overall response rate (ORR), overall survival (OS), and safety. The 12-month PFS rate is 38% (95% CI 27.5-55), not meeting the pre-specified primary endpoint. Serial circulating tumor DNA (ctDNA) analysis reveals decrease and clearance of the original activating EGFR and EGFR-T790M mutations which are prognostic of clinical outcomes. In 73% of participants, loss of T790M ctDNA is observed at progression and no participants have evidence of the EGFR C797S resistance mutation following the alternating regimen. These findings highlight the challenges of treatment strategies designed to modulate clonal evolution and the clinical importance of resistance mechanisms beyond suppression of selected genetic mutations in driving therapeutic escape to highly potent targeted therapies.