Objective: To retrospectively analyze KRAS and BRAF gene mutation features in Chinese colorectal cancer (CRC) and their clinicopathologic relationship.
Methods: 557 colorectal cancer cases were collected, including 325 colon cancer and 232 rectal cancer. PCR amplification and DNA sequencing were used to detect mutations in exon 2 of KRAS gene and exon 15 of BRAF gene mutation.
Results: (1) KRAS mutation was found in 40.4% (225/557) colorectal cancer. The most common mutation locations were in codon 12(79.1%, 178/225) and codon 13 (20.4%, 46/225). The most common mutation types were GGT > GAT (G12D) (37.8%, 85/225), GGT > GTT(G12V) (20.0%, 45/225) in codon 12 and GGC > GAC (G13D) in codon 13 (19.6%, 44/225). These three point mutations accounted 77.3% (174/225) in total KRAS gene mutation cases. All cases showed only one of point mutation types. (2) Among 557 CRC cases, KRAS mutation was significantly higher in female (46.2%, 92/199) than in man (37.2%, 133/358; P < 0.05). KRAS gene codon 13 mutation was higher in right colon cancer (11.3%, 12/106) than that in left colon cancer (4.8%, 6/124), but it didn't show any statistical significance (P > 0.05). (3) BRAF gene mutation was 5.1% (10/197) in colorectal cancer and 8/10 were the point mutation of GTG > GAG (V600E). Eight colorectal cancer cases with GTG > GAG (V600E) were not showing KRAS gene mutation. Both two cases with mutation on codon 600 (GTG > ATG, V600M) and codon 606 (GGG > AGT, G606S) showed codon 12 mutation of KRAS gene. (4) BRAF (V600E) gene mutation was higher in female (8.5%, 6/71) than that in male (1.6%, 2/126; P = 0.05); BRAF mutation in colon cancer (8.3%, 6/72) was higher than that in rectum cancer (2.1%, 2/94), but hadn't statistical significance (P > 0.05).
Conclusions: (1) Codon 12, 13 in KRAS gene and codon 600 in BRAF gene are the most common mutation points in Chinese colorectal cancer. KRAS and BRAF mutations are mutually exclusive. (2) KRAS and BRAF gene mutation is higher in female than that in male, suggesting that RAS-RAF-MAPK signal pathway is probably related to hormones directly or indirectly. (3) There is a trend that codon 13 mutation in KRAS and codon 600 mutation in BRAF in right colon cancer are higher than that in left colon cancer, respectively, however, which needs more cases to be further verified.