Costa Angela M, Herrero Agustín, Fresno Manuel F, Heymann Jonas, Alvarez José Antonio, Cameselle-Teijeiro Jose, García-Rostán Ginesa
Institute of Molecular Pathology and Immunology of Porto University, Porto, Portugal.
Clin Endocrinol (Oxf). 2008 Apr;68(4):618-34. doi: 10.1111/j.1365-2265.2007.03077.x. Epub 2007 Dec 5.
BRAF(V600E) mutation represents the most common oncogenic event in sporadic papillary thyroid cancer (PTC). There are, however, significant discrepancies regarding the overall frequency, its prevalence in PTC-variants, and its relationship with clinico-pathological parameters of poor outcome. Moreover, the impact of BRAF(V600E) mutants on tumour-related patient's death has not been evaluated.
We analysed, by PCR-SSCP and/or PCR-direct sequencing, exons 8, 10, 11 and 15 of BRAF in 113 tumour samples from 49 PTC-patients. Matched lymph node metastases and/or distant metastases (DMs) were screened in 35 patients. Focal changes in the growth pattern or microscopic grade within the primary tumour (Pt) or the metastases were separately genotyped. Mutations at H-, K-, N-ras and PIK3CA exons 9 and 20 were also investigated. For comparison with PTC cases, the BRAF and Ras mutational status was evaluated in 89 specimens obtained from 24 poorly differentiated thyroid carcinomas (PDCs) and 36 anaplastic thyroid carcinomas (ATCs).
BRAF(V600E) was found in 13/16 classical PTCs (CL-PTCs), 6/17 follicular variant PTCs (FV-PTCs) and 8/16 mixed (papillary/follicular) PTCs (Mx-PTCs), being significantly associated with CL-PTCs (P = 0.015). BRAF(V600E) segregated with metastatic PTC-cells in 43% of the patients, but only one DM disclosed the mutation. PTC-tumours featuring concurrent less-differentiated foci were BRAF wild-type in both components. Noteworthy, the frequency of BRAF mutations among PDCs and ATCs resulted considerably lower (16.6% and 25%, respectively) than in PTCs (55%). The prevalence of Ras mutations among PDCs and ATCs (46% and 36%, respectively) was, however, much higher than in PTCs (14%). Five (71%) of the patients who died of PTC displayed somatic mutations. Four of them had other gene alteration associated with BRAF(V600E) and the only one that did not, BRAF(V600E) was restricted to the Pt. The occurrence of BRAF(V600E) associated with other genetic events was an independent predictor of DMs during follow-up, recurrence and tumour-related death. Remarkably, two PDCs (8.3%) and five ATCs (14%) revealed concurrent BRAF and Ras mutations.
BRAF(V600E)'alone' does not represent a marker for poor outcome, however, when associated with alterations in other genes identifies a subset of PTCs with increased risk of recurrence and decreased survival.
BRAF（V600E）突变是散发性乳头状甲状腺癌（PTC）中最常见的致癌事件。然而，在总体发生率、在PTC变体中的患病率及其与不良预后临床病理参数的关系方面存在显著差异。此外，BRAF（V600E）突变体对肿瘤相关患者死亡的影响尚未得到评估。
我们通过PCR-SSCP和/或PCR直接测序分析了49例PTC患者的113个肿瘤样本中BRAF基因的第8、10、11和15外显子。对35例患者的匹配淋巴结转移灶和/或远处转移灶（DMs）进行了筛查。对原发肿瘤（Pt）或转移灶内生长模式或微观分级的局灶性变化分别进行基因分型。还研究了H-、K-、N-ras和PIK3CA基因第9和20外显子处的突变。为了与PTC病例进行比较，在从24例低分化甲状腺癌（PDCs）和36例未分化甲状腺癌（ATCs）获得的89个标本中评估了BRAF和Ras的突变状态。
在13/16例经典PTC（CL-PTC）、6/17例滤泡状变体PTC（FV-PTC）和8/16例混合性（乳头状/滤泡状）PTC（Mx-PTC）中发现BRAF（V600E），与CL-PTC显著相关（P = 0.015）。43%的患者中BRAF（V600E）与转移性PTC细胞分离，但仅1个DM显示该突变。具有同时存在低分化灶的PTC肿瘤在两个成分中均为BRAF野生型。值得注意的是，PDCs和ATCs中BRAF突变的频率（分别为16.6%和25%）明显低于PTCs（55%）。然而，PDCs和ATCs中Ras突变的患病率（分别为46%和36%）远高于PTCs（14%）。5例（71%）死于PTC的患者出现体细胞突变。其中4例有与BRAF（V）600E相关的其他基因改变，唯一没有的1例，BRAF（V600E）仅限于Pt。与其他基因事件相关的BRAF（V600E）的出现是随访期间DMs、复发和肿瘤相关死亡的独立预测因素。值得注意的是，2例PDCs（8.3%）和5例ATCs（14%）显示同时存在BRAF和Ras突变。
BRAF（V600E）“单独”并不代表不良预后的标志物，然而，当与其他基因改变相关时，可识别出复发风险增加和生存率降低的PTC亚组。
