Introduction. The concordance of KRAS gene mutation status between the primary and metastatic CRC is 95%. The aim of this study was to find factors associated with the disconcordance of KRAS, NRAS, BRAF, PIK3CA mutation status between the primary tumors and metastases in pts with CRC. Patients and methods. We performed DNA melting analysis with TaqMan probes and following Sanger sequencing to detect mutation hot-spots in KRAS exons 2 and 3, NRAS exons 2 and 3, BRAF exon 15, PIK3CA exons 9 and 20 in 148 tumor tissues from 65 pts (65 primary tumors and 83 metastases). Results. Mutations in KRAS, NRAS, PIK3CA and BRAF genes in primary tumors were detected in 43.1%, 3.1%, 13.8% and 3.1%, respectively. Discordance of mutation status of genes was identified in 29.2% of patients: 16.9% in KRAS, 3% in NRAS, 12.3% in PIK3CA and 3% BRAF status. In all cases of metastases in the brain we found the discordance in KRAS and PIK3CA mutation status (p=0.08). Also, peritoneal metastases had discordance in KRAS status (p=0.02). With the increase of period from removal of the primary tumor and metastases, the incidence rate of changes in the mutational status of the genes also increased. Conclusion. discordance of the mutational status of genes, especially in the long course of the disease, raises the question of repeating biopsies in the progression of the disease

Objective: to evaluate tolerability and efficacy of maintenance treatment in the absence of progression after 16 weeks of first-line therapy in patients with unresectable metastatic colon cancer.Materials and methods. We have analyzed medical case histories of patients with metastatic colorectal cancer who underwent treatment in the department of clinical pharmacology and chemotherapy of N. N. Blokhin Russian Cancer Research Center from 2007 to 2015 years. Inclusion criteria were the following: 16–24 weeks of first-line chemotherapy with no signs of progression and the inability to perform metastasectomy. Progression-free survival was the main criterion for effectiveness in our study.Results. 160 (44.5 %) of 359 treated patients met the inclusion criteria. 102 (63.7 %) patients were followed up, while the other 58 (36.3 % – comparison group) patients underwent maintenance chemotherapy. Grade I–II toxic reactions and grade III complications associated with first-line chemotherapy were insignificantly more common in the group of patients left on maintenance chemotherapy: 72.4 % and 37.9 % versus 57.8 % and 24.5 % in the comparison group, p = 0.07 and p = 0.07 respectively. The frequency of grade I–II toxic reactions and grade III complications in the second-line treatment did not differ between treatment groups (p = 0.9 and p = 0.8). The median of progression-free survival in observation group and comparison group was 4, and 6 months (odds ratio (OR) 0.6; p = 0.009), and life expectancy – 23 and 31 months (OR 0.75; p = 0.1), respectively. Statistically significant differences between groups with respect to achieving the objective response and/or normalization of carcinoembryonic antigen level were revealed: median of progression-free survival was 13 (n = 26 of 57; 45.6 %) and 4 months (n = 31 of 57, 54.4 %), respectively (HR 0.38; p = 0.002), median of life expectancy – 34 months versus 26 months (OR 0.37; p = 0.3). Conclusions. Carrying out maintenance therapy is associated with increased incidence of grade III complications during the first-line treatment, but does not affect the tolerability of the second-line treatment. Supportive chemotherapy with fluoropyrimidines remains to be the most effective in patients with favorable prognostic factors such as normalization of carcinoembryonic antigen and/or achievement of the objective response on the background of first-line chemotherapy.

Objective : to evaluate tolerability and efficacy of maintenance treatment in the absence of progression after 16 weeks of first-line therapy in patients with unresectable metastatic colon cancer. Materials and methods . We have analyzed medical case histories of patients with metastatic colorectal cancer who underwent treatment in the department of clinical pharmacology and chemotherapy of N. N. Blokhin Russian Cancer Research Center from 2007 to 2015 years. Inclusion criteria were the following: 16–24 weeks of first-line chemotherapy with no signs of progression and the inability to perform metastasectomy. Progression-free survival was the main criterion for effectiveness in our study. Results. 160 (44.5 %) of 359 treated patients met the inclusion criteria. 102 (63.7 %) patients were followed up, while the other 58 (36.3 % – comparison group) patients underwent maintenance chemotherapy. Grade I–II toxic reactions and grade III complications associated with first-line chemotherapy were insignificantly more common in the group of patients left on maintenance chemotherapy: 72.4 % and 37.9 % versus 57.8 % and 24.5 % in the comparison group, p = 0.07 and p = 0.07 respectively. The frequency of grade I–II toxic reactions and grade III complications in the second-line treatment did not differ between treatment groups (p = 0.9 and p = 0.8). The median of progression-free survival in observation group and comparison group was 4, and 6 months (odds ratio (OR) 0.6; p = 0.009), and life expectancy – 23 and 31 months (OR 0.75; p = 0.1), respectively. Statistically significant differences between groups with respect to achieving the objective response and/or normalization of carcinoembryonic antigen level were revealed: median of progression-free survival was 13 (n = 26 of 57; 45.6 %) and 4 months (n = 31 of 57, 54.4 %), respectively (HR 0.38; p = 0.002), median of life expectancy – 34 months versus 26 months (OR 0.37; p = 0.3). Conclusions . Carrying out maintenance therapy is associated with increased incidence of grade III complications during the first-line treatment, but does not affect the tolerability of the second-line treatment. Supportive chemotherapy with fluoropyrimidines remains to be the most effective in patients with favorable prognostic factors such as normalization of carcinoembryonic antigen and/or achievement of the objective response on the background of first-line chemotherapy.