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.

Background Resistance on the 1st or 2nd generation TKIs in patients with EGFR mutated NSCLC to the therapy occurs on average after 8-12 months. The most common (49-60%) resistance mechanism is the appearance of the T790M. Its determination is possible by different methods of examination: ctDNA (false-negative probability 23%) and tumor tissue (sensitivity of 88%). The appointment of osimertinib in the second line allows to increase ORR, but also PFS relative to standard chemotherapy. Methods In this study we investigated the effect on PFS by the dynamic determination of ctDNA. Included patients with metastatic EGFR-associated NSCLC, in whom, a T790M mutation was detected during treatment TKIs of 1-2 generations.Patients received osimertinib therapy 80 mg / day, daily, until progression of the disease appears. Blood test was taken to conduct a qualitative assessment of ctDNA in dynamics by the RT-PCR method, fist test was done before starting treatment, and then every 2 months. Results From August 2016 to December 2018, 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 – 18.9 months (CI 95%, 10.6 - 27.1). In 12/22 patients was observed the disappearance of ctDNA T790M + after 2 months of osimertinib therapy. PFS is 24.4 months (CI calculation is NA), 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 7.6 months) (CI 95%, 3.0 –12.9) (p = 0.003). The confidence interval for one of the medians cannot be calculated the 75% percentile was 3.4 +/- 3.3 and 18.8 +/- 6.3. 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 + Grant supported RUSSCO / RakFond 2018-01-YS-ECI. Legal entity responsible for the study St. Petersburg Clinical Research Center of Specialized Types of Care (Oncology). Funding Has not received any funding. Disclosure All authors have declared no conflicts of interest.

Background Osimertinib (Osi) is a 3rd generation TKI that crosses the blood-brain barrier (BBB), which has been shown to be effective in both the second and first line of treatment in patients with NSCLC with an EGFR mutation. In use of Osi in patients with T790M associated progression during therapy with earlier TKIs, the median PFS was 10.1 months. The duration of treatment may vary significantly for each patient. The study of the mechanisms of resistance to 3rd generation TKIs is the subject of clinical studies, among the most common variants of resistance - the appearance of the gate-keeper mutation C797S - in 7% of cases. Methods It is prospective, single-center study we examined the appearance of resistance in patients receiving Osi treatment.The search for the C797S mutation was carried out using an original diagnostic platform based on real-time PCR, using the BioRad Real-Time CFX96 amplifier. Primers and fluorescent probes were synthesized by Applied Biosystems compony. The study included patients with progression during therapy with Osi. Before treatment, and then every 2 months until progression of the disease appease, blood sampling was performed to conduct a qualitative assessment of ctDNA (ex19del, L858R, T790M, C797S). Results From August 2016 to August 2019, in 12/22 patients, progression of the disease during the Osi. Emong them, 66.7% (7/12) are women, 33.3% (4/12) are men. The average age is 64.6 years (55-80). 1/12 smoked for over 30 years. The molecular genetic profile in 58.3% (7/12) of the patients is ex19del, 33.3% (4/12) of L858R, 8.4% (1/12) is a combination of rare mutations G719S + S768I. The median PFS during the Osi treatment was 9.6 months. (0.7 - 18.4).The analysis of ctDNA was performed in 11/12 patients: an activated mutation was detected in all cases, 1/12 recorded the mutation C796S (NGS), T790M and C797S (cis/ trans) were not detected.Histological material was taken from 4/12 patients, 2 of which showed the transformation of the tumor into small cell lung cancer. Conclusions The investigation of appearence the resistance mechanisms in the treatment with osimertinib did not reveal the EGFR C797S mutation, which may be associated with a small number of patients included in the study.Grant supported RUSSCO / RakFond 2018-01-YS-ECI. Legal entity responsible for the study St. Petersburg Clinical Research Center of Specialized Types of Care (Oncology). Funding RakFond (Russia). Disclosure All authors have declared no conflicts of interest.

The analysis of the circulating tumor DNA has attracted interest in the last 6-7 years and is being actively introduced into everyday practice. "Liquid biopsy" will eliminate the shortcomings of routine biopsy, accelerate the time of clinical decision-making, to conduct a more comprehensive study of the tumor in terms of personification of treatment and development of resistance. Results of liquid biopsy provide real-time information on the molecular pathologies and morphological features, identify early resistance to treatment and can modify the therapy regimen. From 2016 to 2018 year we studied patients with NSСLC. The ctDNA was detected in the baseline plasma samples and then every 2 months after treatment started by RT-PCR. The aim of the study was to assess the relationship between the presence of EGFR positive ctDNA in tumor tissue and blood plasma The study was 1050 patients, 462 cases are represented by adenocarcinoma of NSCLC. EGFR mutations was detected in 145/462 cases (31.38%). Among 145 person 109 were women (72.5%) and 36 were men (24.8%). The mean age was 65.18 (35 - 85). The mutational profile was heterogeneous: ex19del – 94/145 (63.8%), L858R – 47/145 (32.4%), others – 4/145 (2.8%). The results of the study demonstrated that analyzing ctDNA from plasma is feasible for the identification of EGFR mutations with mutation status concordance in 79 matched samples of 53.2% (EGFR mutation positive was detected in 42/79 samples). The T790m resistance mutation was detected in the baseline plasma sample in 8/79 cases (10.1%). EGFR-activating mutations were identified in 13/56 (23.3%) plasma samples after 2 months of Gefitinib. Among the 42 patients in whom the сtDNC was detected in the baseline, after 2 months of therapy was determined only in 6/42 (14.2%). Thus, the disappearance of the mutation was observed in 85.71% (36/42). Mediana of PSF for patients who retained ctDNA after 2 months was 16.25 months (Cl 95% 11.24 – 19.94), and for patients in whom the mutation disappeared after 2 months was 21.10 (Cl 19.21 - 22.98). Currently the study of molecular genetic markers in blood plasma are continuing. The relationship between effectiveness of treatment and ctDNA detection in blood samples will be analyzed. This new, minimally invasive method has the potential to change the prognostic and predictive landscape for lung cancer genotyping and patient management, which will improve treatment outcomes

The third generation TKI (osimertinib) according to AURA III trial results achieved longer PFS compared to standard platinum based chemotherapy in patient's resistant to 1-2 generation TKIs due to T790M mutation (8.5 vs 4.2 months). The evolution of resistance profile during thins therapy can be analyzed based on ctDNA. In this study patients with metastatic EGFR mutated NSCLC, with a confirmed disease progression during treatment with 1/2 generation TKIs, T790M positive which included patients received osimertinib 80 mg daily. Before the treatment and then every 2 months, whole blood was taken, for qualitative assessment of ctDNA dynamics by RT-PCR. The aim of the study was to assess the relationship between the disappearance of T790M + ctDNA and the time to progression on osimertinib. From August 2016 to December 2018 22 patients with T790M positive progression were identified. 18/22 (81.9%) were women, 4/22 (18.1%) - men. The mean age was 61.2 years (50-75). Only 1/22 had a smoking history >30 pack/years. Primary activating mutations in EGFR gene were ex19del, L858R and G719S + S768I in 16, 5 and 1 patients respectively. Median PFS on the first line TKI was 21.7 months (CI 95%, 10.8 – 53.3). In 59.1% (13/22) progressive disease was characterized by the appearance of new metastases and in 40.9% (9/22) by the growth of previously identified metastases. 22 patients were evaluable for response. PR and SD were achieved in 11/20 (50%) and 10/20 (45/5%) respectively. Median PFS was in a whole group 16.7 months (CI 95%, 11.4 - 22.0). T790M in ctDNA was negative after 2 months of osimertinib treatment in 12/22 patients. Median PFS was 18.9 months (CI 95%, 14.8–19.7) in patients with undetectable T790M in ctDNA after 2 month of therapy compared to 8.0 months (CI 95%, 4.2 – 11.8) in patients remaining ctDNA T790M positive. No clinical factors were associated with the disappearance of ctDNA by statistical analysis. The disappearance of T790M + ctDNA after 2 months osimertinib therapy is predictive of greater PFS in patients with EGFR mutation positive NSCLC, receving of 2nd line.