e15514 Background: The standard treatment of squamous cell carcinoma of the tongue and the mucosa of the bottom of the oral cavity (SCCTOM) is chemotherapy (CT) in combination with cetuximab (mC, anti-EGFR antibody). However, not all patients manage to achieve positive results. A common cause of resistance to anti-EGFR antibodies is the constitutive activation of mediators of the underlying signaling pathways. Therefore, the aim of the study was to analyze mutations in the KRAS using the Digital Droplet PCR method in patients with SCCTOM on the background of CT in combination with targeted therapy or standard CT. Methods: The study used the QX200 system (Bio-Rad) and the ddPCRtm KRAS Screening Multiplex Kit (7 mutations). The study included 60 patients with T3-4N0-1M0 SCCTOM. The main group consisted of 30 patients (cisplatin, 5-fluorouracil+cetuximab). The control group consisted of 30 patients (CT). For research, cfDNA from blood plasma was used. Analysis of the data was performed using QuantaSoft v1.7.4. Results: The frequency of the KRAS mutant type (mtKRAS) is 43% before treatment and 32% after treatment (n = 60). In the group of patients CT+mC the incidence of mtKRAS before treatment was 40%, after treatment - 20%. In the group of patients CT without mC the incidence of mtKRAS before treatment was 47%, after treatment - 43%. Decrease of 20% (p = 0.00089) in the frequency of mtKRAS after CT+mC was found, while it was 23% (p = 0.00009) lower than the frequency of mtKRAS after CT without mC. After treatment, in the CT+mC group of patients, the number of mtKRAS DNA copies increased 1.5 times (p = 0.048). Analysis of clinical response to therapy allowed us to divide the main and control groups of patients into 2: sensitive and resistant to therapy. After treatment, a change in the mtKRAS ratio was not found in the subgroup sensitive to mC compared with the period before treatment, while the frequency of mtKRAS was reduced by 3 times (p = 0.009). In the mC-resistant subgroup, the mtKRAS ratio increased 1.9 times compared to the period before treatment (p = 0.009), while the frequency of mtKRAS increased 3.5 times compared with the mC-sensitive group (p = 0.0045). Conclusions: Prior to treatment, patients resistant to CT+mC were characterized by an increased occurrence of mutations in the KRAS and an apparently large number of tumor cells carrying mutations. The use of mCs caused a change in the direction of the clonal evolution of tumor cells - leading to an increase in the number of cells carrying mtKRAS (conditions were created for the elimination of cells with mutation in EGFR and KRAS wild type).
Clonal evolution and progression of 20-methylcholanthrene-induced squamous cell carcinoma of mouse epidermis as revealed by DNA instability and other malignancy markers
