The effect of drug therapy and cetuximab on the mutational status of the KRAS gene in patients with squamous cell carcinoma of the tongue and oral floor mucosa

Background. Squamous cell carcinoma of the tongue and oral floor mucosa is one of the most common localizations of tumors of the head and neck, which is characterized by rapid growth, aggressive course, high mortality, and unfavorable prognosis. Objective. Determination of activating mutations in the KRAS gene in the extracellular DNA of blood plasma in patients with squamous cell carcinoma of the tongue and oral floor mucosa during chemotherapy (CT) with targeted therapy with cetuximab or during standard CT without targeted therapy. Methods. Data on 60 patients who underwent chemotherapy in combination with targeted therapy with cetuximab or standard chemotherapy were analyzed. Depending on the effectiveness of treatment, all patients, according to the RECIST 1.1 criteria, were divided into 2 subgroups: sensitivity to treatment (partial regression and stabilization), and resistance (progression). Before the start of antitumor treatment and after 2 cycles, blood samples with a volume of 9 ml were collected in 2 stages. Plasma was isolated by double centrifugation. All extracellular DNA samples were isolated from blood plasma according to the protocol using the cobas cfDNA Sample Preparation Kit. The presence/absence of 7 activating mutations in the second exon of the KRAS gene was detected by Digital Droplet PCR using the KRAS Screening Multiplex kit (Bio-Rad, USA). The data were analyzed using the QuantaSoft v1.7.4 software. Results. It was revealed that when resistance to chemotherapy and cetuximab develops, the ratio of the mutant KRAS type increased by 1.9 times compared to the initial values (p=0.009), exceeding the same indicator in the subgroup with sensitivity by 3.1 times (p=0.049), while the frequency of occurrence of the mutant type of the KRAS gene in the studied sample decreased by 1.5 times (p=0.05), and increased by 3.5 times compared with the subgroup with sensitivity (p=0.0045). The use of cetuximab resulted in a decrease in the frequency of mutations in the KRAS gene and in an increase in the ratio of the number of DNA copies of the mutant KRAS type to the wild type. Conclusion. Thus, it can be concluded that even before the start of treatment, patients resistant to chemotherapy and cetuximab were characterized by an increased occurrence of mutations in the KRAS gene and, obviously, a large number of tumor cells carrying mutations in this gene. Determination of activating mutations in the KRAS gene in the extracellular DNA of blood plasma makes it possible to predict the development of resistance to targeted therapy at the stages of treatment.

KRAS, tongue cancer, cancer of the oral floor mucosa, KRAS, extracellular DNA, chemotherapy, cetuximab, sensitivity, resistance