Correlation of the KRAS gene’s copy number variation and the results of targeted therapy for colorectal cancer

BACKGROUND: to find predictive value of KRAS gene’s copy number variation (CNV_KRAS) to anti-EGFR therapy.
PATIENTS AND METHODS: a prospective cohort single-center study included 150 patients, 103 patients with colorectal cancer (CRC) and wild-type RAS/BRAF, 39 patients with colorectal cancer with somatic mutations in the KRAS gene, as well as 8 non-oncological patients (as normal controls). CNV_KRAS was determined using digital droplet PCR.
RESULTS: the clinically significant CNV_KRAS level of ≥ 9 copies established for a refusal of targeted anti-EGFR therapy. The incidence of clinically significant CNV_KRAS level in patients with wild-type RAS/BRAF was 17% (the first group of patients). Incidence of clinically significant CNV_KRAS level in patients with mutations in the KRAS gene was 3% (the second group of patients). At the I stage of CRC clinically significant CNV_KRAS was not detected in either the first or second group; at the stage II of CRC in the first group — in 14% of patients (3/22), and in the second group — not detected; at the stage III of CRC in the first group — in 21% of patients (8/39), and in the second group of patients — not detected; at the stage IV of CRC in the first group — in 17% (6/35) of patients, and in the second group of patients — in 5% (1/20). Tumor DNA was analyzed in 10 patients with the stage IV CRC from the first group who received anti-EGFR therapy to find out the clinically significant level of CNV_KRAS. Disease control was achieved in 7 out of 10 patients. The median CNV_KRAS score in the remaining three patients was higher than in the disease control group, 9.2 (9.05, 10.10) and 5.38 (4.77, 7.35) (p = 0.017).
CONCLUSIONS: detection of CNV_KRAS level of ≥ 9 copies in a malignant colon tumor is a contraindication to targeted therapy. This phenomenon occurs significantly more often in patients without somatic mutations in the RAS genes (KRAS, NRAS) and BRAF, than in patients with point mutations in the KRAS gene (p = 0.02).

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