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Purpose This study aimed to analyze changes in the plasma concentration of EGFR-mutated circulating tumor DNA (ctDNA) occurring immediately after the start of therapy with EGFR tyrosine kinase inhibitors (TKIs). Methods Serial plasma samples were collected from 30 patients with EGFR-driven non-small cell lung cancer before intake of the first tablet and at 0.5, 1, 2, 3, 6, 12, 24, 36 and 48 h after the start of the therapy. The content of EGFR alleles (exon 19 deletions or L858R) in ctDNA was measured by ddPCR. Results ctDNA was detected at base-line in 25/30 (83%) subjects. Twelve (50%) out of 24 informative patients showed > 25% reduction of the ctDNA content at 48 h time point; all these patients demonstrated disease control after 4 and 8-12 weeks of therapy. The remaining 12 individuals showed either stable content of EGFR-mutated ctDNA (n = 5) or the elevation of ctDNA concentration (n = 7). 10 of 12 patients with elevated or stable ctDNA level achieved an objective response at 4 weeks, but only 5 of 10 evaluable patients still demonstrated disease control at 8-12 weeks (p = 0.032, when compared to the group with ctDNA decrease). The decline of the amount of circulating EGFR mutant copies at 48 h also correlated with longer progression-free survival (14.7 months vs. 8.5 months, p = 0.013). Conclusion Comparison of concentration of EGFR-mutated ctDNA at base-line and at 48 h after the start of therapy is predictive for the duration of TKI efficacy.

Despite the unprecedented success in using immune checkpoint inhibitors in the treatment of lung cancer, melanoma, hypermutable tumors of various localization, etc., a significant proportion of patients receiving these drugs do not respond to treatment. Predictive markers routinely used in the selection of patients for immunotherapy, in particular, the level of expression of PD -L1 and the presence of microsatellite instability, have certain limitations. Over the past decade, many other biomarkers designed to predict response to immunotherapy have been proposed, namely: tymor mutation burden, composition of lymphocytic infiltrate; allelic composition of the major histocompatibility complex; relationship between the numbers of different formed elements of blood as well as between its biochemical parameters; microflora of the digestive tract, etc. These markers can directly or indirectly reflect the immunogenicity of the tumor itself, as well as the state of systemic and intratumoral immune response. The predictive power and reliability of these markers are extremely different. When preparing this review, we conducted a literature search for recent studies regarding predictors of efficacy for immune checkpoint inhibitors published in the journals included in the databases, such as Pubmed, Web of Science, and Scopus.