Human Cancer Genomic Research, Research Center, King Faisal Specialist Hospital and Research Centre, Riyadh 11211, Saudi Arabia.
J Pathol. 2009 Dec;219(4):435-45. doi: 10.1002/path.2625.
Somatic KRAS mutation is an early well-known event in colorectal carcinogenesis but a complete understanding of RAS function and dysfunction in colorectal cancer is still to come. Our aim was to study the incidence of KRAS mutation; KRAS splice variants: KRAS4A and KRAS4B; and their relationships with various clinico-pathological characteristics in colorectal cancer (CRC).In this study, 285 CRC cases were analysed for KRAS mutation by direct DNA sequencing followed by immunohistochemical analysis after validation with real-time PCR assay, to study the protein expression of KRAS4A and -4B isoforms. KRAS gene mutations were seen in 80/285 CRCs (28.1%) and of the mutated cases, the majority of the mutations were seen in codon 12 (81.2%) as opposed to codon 13 (18.8%). CRCs with KRAS mutations were associated with a poor overall survival (p = 0.0009). Furthermore, KRAS mutations at codon 12 were associated with a poor overall survival of 64.4% at 5 years compared with a 5-year overall survival of 75.8% and 78.2% with codon 13 mutation and absence of KRAS mutations, respectively (p = 0.0025). KRAS4A protein expression was predominantly seen in the cytoplasm, while KRAS4B protein was nuclear. KRAS4A overexpression was significantly associated with left colon, histology subtype of adenocarcinoma, p27kip1, and cleaved caspase3 expression. Interestingly, KRAS4A overexpression was associated with a better overall survival (p = 0.0053). On the other hand, KRAS4B overexpression (33.2%) was significantly associated with larger tumour size (p = 0.0234) and inversely correlated with p27kip1 protein (p = 0.0159). Both KRAS mutation and KRAS4A were independent prognostic markers in a multivariate analysis with age, gender, stage, differentiation, and MSI status. Our results highlight the differential role of KRAS isoforms in CRC, their utility as a prognostic biomarker, and underline the importance of KRAS alterations as a potential therapeutic target for CRC.
体细胞 KRAS 突变是结直肠癌发生过程中一个早期的、众所周知的事件，但对 RAS 功能和功能障碍在结直肠癌中的作用仍有待进一步研究。我们的目的是研究 KRAS 突变、KRAS 剪接变异体：KRAS4A 和 KRAS4B 以及它们与结直肠癌（CRC）各种临床病理特征的关系。在这项研究中，通过直接 DNA 测序分析了 285 例 CRC 病例的 KRAS 突变，随后通过实时 PCR 检测进行验证，研究了 KRAS4A 和 -4B 异构体的蛋白表达。在 285 例 CRC 中，有 80 例（28.1%）存在 KRAS 基因突变，其中大多数突变发生在密码子 12（81.2%），而不是密码子 13（18.8%）。KRAS 突变的 CRC 与整体生存率差相关（p = 0.0009）。此外，KRAS 密码子 12 突变与较差的总生存率相关，5 年总生存率为 64.4%，而密码子 13 突变和无 KRAS 突变的 5 年总生存率分别为 75.8%和 78.2%（p = 0.0025）。KRAS4A 蛋白表达主要见于细胞质，而 KRAS4B 蛋白表达见于核内。KRAS4A 过表达与左结肠、腺癌组织学亚型、p27kip1 和 cleaved caspase3 表达显著相关。有趣的是，KRAS4A 过表达与更好的总体生存率相关（p = 0.0053）。另一方面，KRAS4B 过表达（33.2%）与肿瘤较大的大小显著相关（p = 0.0234），并与 p27kip1 蛋白呈负相关（p = 0.0159）。在多变量分析中，KRAS 突变和 KRAS4A 是独立的预后标志物，包括年龄、性别、分期、分化和 MSI 状态。我们的研究结果突出了 KRAS 异构体在 CRC 中的不同作用，它们作为预后生物标志物的作用，以及 KRAS 改变作为 CRC 潜在治疗靶点的重要性。
