Thebo J S, Senagore A J, Krygier S, Luchtefeld M A
Spectrum Health, Grand Rapids, Michigan, USA.
Am Surg. 2001 Aug;67(8):802-5.
The clonal development of colorectal carcinoma resulting from specific mutations in certain oncogenes and/or tumor suppressor genes is a well-accepted model. It is increasingly recognized that a majority of colorectal cancers are polyclonal on the basis of molecular analysis that demonstrates cells with different mutations within a given oncogene or tumor suppressor gene in the same tumor. This polyclonal pattern may occur as a result of either clonal convergence or divergence during the many steps of oncogenesis. Further complicating this picture is the fact that metastatic lesions may arise from only one of the clonal populations within a tumor and thereby present only a partial molecular make-up of the whole tumor. There are few data available that define clonal selection or specificity of circulating tumor cells in patients undergoing curative resection of colorectal carcinoma. The purpose of this paper is to describe the clonal distribution of circulating tumor cells in four patients with multiple K-ras mutations present in the primary lesion. Patients were selected who were known to have polyclonal primary colorectal cancers resected for cure. All patients had multiple mutations present in exon one, codon 12 and/or 13, of the K-ras gene. Blood samples were drawn immediately before surgery and at 2-week to 6-month intervals postoperatively. Epithelial cells were isolated from peripheral blood mononuclear cells using Dynal Immunobeads coated with antiepithelial antibodies. DNA was extracted from these cells and analyzed for all K-ras mutations present in codons 12 and 13 of the patient's primary tumor using allele-specific polymerase chain reaction followed by Microwell Array Diagonal Gel Electrophoresis. Circulating tumor cells were identified in all four patients. However, in each case of positive circulating cells the only mutation identified was an aspartic acid mutation at codon 13. Once positive the circulating tumor cells persisted in subsequent multiple blood samples. These results provide further strength for the theory of polyclonal progression in primary colorectal cancers, although there may be specific mutational patterns that confer the ability to metastasize. The significance of this persistence of the glycine-to-aspartic acid mutation at codon 13 remains to be defined given that none of these patients has clinical evidence of recurrent cancer at the time of this report.
由某些癌基因和/或肿瘤抑制基因的特定突变导致的结直肠癌克隆性发展是一个被广泛接受的模型。基于分子分析，越来越多的人认识到大多数结直肠癌是多克隆性的，这种分析表明同一肿瘤中给定癌基因或肿瘤抑制基因内存在不同突变的细胞。这种多克隆模式可能是肿瘤发生许多步骤中克隆趋同或趋异的结果。使情况更加复杂的是，转移灶可能仅源于肿瘤内的一个克隆群体，因此仅呈现整个肿瘤的部分分子组成。关于接受结直肠癌根治性切除的患者中循环肿瘤细胞的克隆选择或特异性，可用数据很少。本文的目的是描述4例原发灶存在多个K-ras突变的患者中循环肿瘤细胞的克隆分布。选择已知接受了根治性切除的多克隆原发性结直肠癌患者。所有患者的K-ras基因第1外显子的密码子12和/或13存在多个突变。术前即刻以及术后每隔2周或6个月采集血样。使用包被抗上皮抗体的Dynal免疫磁珠从外周血单核细胞中分离上皮细胞。从这些细胞中提取DNA，并使用等位基因特异性聚合酶链反应，随后进行微孔阵列对角线凝胶电泳，分析患者原发肿瘤密码子12和13中存在的所有K-ras突变。在所有4例患者中均鉴定出循环肿瘤细胞。然而，在每例循环细胞阳性的病例中，唯一鉴定出的突变是密码子13处的天冬氨酸突变。一旦呈阳性，循环肿瘤细胞在随后的多个血样中持续存在。这些结果为原发性结直肠癌多克隆进展理论提供了进一步的证据，尽管可能存在赋予转移能力的特定突变模式。鉴于在本报告时这些患者均无癌症复发的临床证据，密码子13处甘氨酸向天冬氨酸突变的这种持续性的意义仍有待确定。
