转移性结直肠癌中 KRAS、NRAS、BRAF 和 PIK3CA 突变的异质性及其对 CAPRI GOIM 试验中治疗的潜在影响。

Heterogeneity of KRAS, NRAS, BRAF and PIK3CA mutations in metastatic colorectal cancer and potential effects on therapy in the CAPRI GOIM trial.

机构信息

Cell Biology and Biotherapy Unit, Istituto Nazionale Tumori 'Fondazione Giovanni Pascale' IRCCS, Napoli Laboratory of Pharmacogenomics, Centro di Ricerche Oncologiche di Mercogliano (CROM)-Istituto Nazionale Tumori 'Fondazione Giovanni Pascale' IRCCS, Napoli

Laboratory of Pharmacogenomics, Centro di Ricerche Oncologiche di Mercogliano (CROM)-Istituto Nazionale Tumori 'Fondazione Giovanni Pascale' IRCCS, Napoli.

出版信息

Ann Oncol. 2015 Aug;26(8):1710-4. doi: 10.1093/annonc/mdv176. Epub 2015 Apr 7.

DOI:10.1093/annonc/mdv176

PMID:25851630

Abstract

BACKGROUND

Evidence suggests that metastatic colorectal carcinoma (mCRC) has a high level of intratumor heterogeneity. We carried out a quantitative assessment of tumor heterogeneity for KRAS, NRAS, BRAF and PIK3CA mutations, in order to assess potential clinical implications.

PATIENTS AND METHODS

Tumor samples (n = 182) from the CAPRI-GOIM trial of first-line cetuximab + FOLFIRI in KRAS exon-2 wild-type mCRC patients were assessed by next-generation sequencing that allows quantitative assessment of mutant genes. Mutant allelic frequency was normalized for the neoplastic cell content and, assuming that somatic mutations usually affect one allele, the Heterogeneity Score (HS) was calculated by multiplying by 2 the frequency of mutant alleles in neoplastic cells. Therefore, HS virtually corresponds to the fraction of neoplastic cells carrying a specific mutation.

RESULTS

The KRAS HS ranged between 12 and 260 with mean value of 87.1 and median value of 84.4, suggesting that in most CRC, the majority of neoplastic cells carry mutant KRAS. Similar findings were observed for NRAS (HS range 35.5-146.7; mean 102.8; median 117.1). In contrast, in BRAF (HS range 17.1-120; mean 54.8; median 54.3) and PIK3CA (HS range 14.3-120; mean 59.5; median 47.3) mutant cases, only a fraction of neoplastic cells seem to carry the mutant allele. The response rate was 70% in KRAS mutant patients with an HS <33 (low KRAS; n = 10) and 45.7% in KRAS HS >33 patients (high KRAS; n = 35); median progression-free survival were 7.97 and 8.37 months, respectively. Low-KRAS tumors had a higher frequency of additional mutations in PIK3CA when compared with high-KRAS (6/10 versus 8/35).

CONCLUSIONS

KRAS and NRAS mutations are usually present in the majority of neoplastic cells, whereas BRAF and PIK3CA mutations often affect a limited fraction of transformed cells. Resistance to cetuximab in low-KRAS patients might be driven by the complex mutational profile rather than KRAS mutation load.

摘要

背景

有证据表明，转移性结直肠癌（mCRC）具有高度的肿瘤内异质性。我们对 KRAS、NRAS、BRAF 和 PIK3CA 突变进行了定量评估，以评估其潜在的临床意义。

患者和方法

对 CAPRI-GOIM 试验中一线使用西妥昔单抗+FOLFIRI 治疗 KRAS 外显子 2 野生型 mCRC 患者的 182 例肿瘤样本进行了下一代测序评估，该方法允许对突变基因进行定量评估。通过将肿瘤细胞含量标准化来评估突变等位基因的频率，并假设体细胞突变通常会影响一个等位基因，那么异质性评分（HS）可以通过将肿瘤细胞中突变等位基因的频率乘以 2 来计算。因此，HS 实际上对应于携带特定突变的肿瘤细胞的分数。

结果

KRAS 的 HS 范围为 12 至 260，平均值为 87.1，中位数为 84.4，表明在大多数 CRC 中，大多数肿瘤细胞携带 KRAS 突变。NRAS 的结果与之类似（HS 范围为 35.5-146.7；平均值为 102.8；中位数为 117.1）。相反，在 BRAF（HS 范围为 17.1-120；平均值为 54.8；中位数为 54.3）和 PIK3CA（HS 范围为 14.3-120；平均值为 59.5；中位数为 47.3）突变病例中，只有一部分肿瘤细胞似乎携带突变等位基因。KRAS 突变患者的 HS<33（低 KRAS；n=10）的客观缓解率为 70%，而 KRAS HS>33 患者的客观缓解率为 45.7%（高 KRAS；n=35）；中位无进展生存期分别为 7.97 个月和 8.37 个月。与高 KRAS 相比，低 KRAS 肿瘤中 PIK3CA 的额外突变频率更高（6/10 例与 8/35 例）。