Predictive value of the dynamic determination of circulating tumor dna on pfs in patients with egfr mutated nsclc, with osimertinib therapy

Aim: study of the predictive value of determining ctDNA during treatment with osimertinib in patients with NSCLC with EGFR mutation. Methods: The study included patients with metastatic EG-FR-associated NSCLC, in whom, with progression against the background of 1st - 2nd generation TKIs, the T790M mutation was detected. Patients received osimertinib therapy 80 mg/ day, daily, until progression. Before treatment, and then every 2 months, whole blood was taken to conduct a qualitative assessment of ctDNA in dynamics by the RT-PCR method. Results: From 2016 to 2019 in St. Petersburg Clinical Scientific and Practical Center of Specialized Types of Medical Care (Oncology), 22 patients were identified T790M associated progression of EGFR NSCLC. 81.9% (18/22) are women, 18.1% (4/22) are men. The average age is 61.2 years (50-75). 1/22 had smoking experience for more than 30 years. The molecular genetic profile in 16 is represented by ex19del, 5 L858R, 1 -a combination of rare mutations G719S+S768I. The effect of therapy was evaluated in 20/22 patients. PR and SD were registered in 9/20 (45%) and 10/20 (50%) patients, respectively. Median PFS - 16.7 months (cI 95%, 11,4-22,0). In 12/22 patients was observed the disappearance of ctDNA T790M after 2 months of osimertinib therapy. PFS is 18,9 months (95% CI, 14,8-19,7), in patients with no mutation detected in the second month of treatment compared with the group of patients in which the ctDNA was determined (PFS 8.0 months) (CI 95%, 4,2-11,8) (p=0.015). Correlation analysis did not reveal any clinical factors associated with the disappearance of ctDNA. Conclusions: The disappearance of ctDNA in plasma after 2 months of treatment with osimertinib is associated with an increase in PFS and can be considered as a predictive marker in patients with metastatic NSCLC EGFR T790M.