KRAS and BRAF mutation status in circulating colorectal tumor cells and their correlation with primary and metastatic tumor tissue

Although anti‐EGFR therapy has established efficacy in metastatic colorectal cancer, only 10‐20% of unselected patients respond. This is partly due to KRAS and BRAF mutations, which are currently assessed in the primary tumor. To improve patient selection, assessing mutation status in circulating tumor cells (CTCs), which possibly better represent metastases than the primary tumor, could be advantageous. We investigated the feasibility of KRAS and BRAF mutation detection in colorectal CTCs by comparing three sensitive methods and compared mutation status in matching primary tumor, liver metastasis and CTCs. CTCs were isolated from blood drawn from 49 patients before liver resection using CellSearch?. DNA and RNA was isolated from primary tumors, metastases and CTCs. Mutations were assessed by co‐amplification at lower denaturation temperature‐PCR (Transgenomic?), real‐time PCR (EntroGen?) and nested Allele‐Specific Blocker (ASB‐)PCR and confirmed by Sanger sequencing. In 43 of the 49 patients, tissue RNA and DNA was of sufficient quantity and quality. In these 43 patients, discordance between primary and metastatic tumor was 23% for KRAS and 7% for BRAF mutations. RNA and DNA from CTCs was available from 42 of the 43 patients, in which ASB‐PCR was able to detect the most mutations. Inconclusive results in patients with low CTC counts limited the interpretation of discrepancies between tissue and CTCs. Determination of KRAS and BRAF mutations in CTCs is challenging but feasible. Of the tested methods, nested ASB‐PCR, enabling detection of KRAS and BRAF mutations in patients with as little as two CTCs, seems to be superior.     

Clinico-pathological correlation of serial measurement of circulating tumor cells in 24 metastatic colorectal cancer patients receiving chemotherapy reveals interpatient heterogeneity correlated with CEA levels but independent of KRAS and BRAF mutation

Background: The Veridex CellSearch is an FDA-approved technology for enumerating circulating tumor cells in blood samples of metastatic colorectal cancer mCRC) patients and has prognostic value. It is important to understand how counts of circulating tumor cells (CTCs), which are advocated to be tools for “liquid biopsy” of tumors, correlate with clinical and pathologic variables of significance in these patients. In this study, we have attempted to make such correlations along with evaluating how CTC counts change during the course of chemotherapy. Patients and methods: Following an IRB-approved protocol, blood samples were collected from 24 patients with mCRC along with relevant clinico-pathological data. Blood was collected at defined time-points both prior to as well as during the course of treatment with combination chemotherapy, and CTC counts were enumerated from7.5 ml of blood. Results: Seventeen out of 24 patients with mCRC showed a CTC count of 2 or less cells in 7.5 ml of blood at base-line assessment before chemotherapy while 7 patients showed 3 or more cells in 7.5 ml of blood at that point. A correlation was found between high carcino-embryonic antigen (CEA) levels and high CTC counts (P = 0.018) although it was also found that some patients had elevated CTCs without an elevated CEA. No correlation with the time interval between detection of primary tumor and appearance of secondary (metastatic) tumor(s) was found. CTC counts did not correlate with the presence of lung or liver metastases, i.e. a number of mCRC patients with lung or liver metastases had a count of zero CTCs at baseline. We also noted no correlation between CTC number and the status of KRAS or BRAF mutation. CTC counts dropped immediately after the start of chemotherapy in 11 out of 21 patients, and also reduced from the baseline at the end of chemotherapy in 5 out of 10 patients. Six of 7 patients who started with 3 or more CTCs in 7.5 ml at baseline also showed a final CTC reduction at the end of the therapy assessment. Conclusions: Analysis of circulating tumor cells may be of use in monitoring response to therapy in mCRC, either in combination with CEA monitoring or alone when CTCs are elevated but CEA level is not.     

Development of molecular biomarkers in individualized treatment of colorectal cancer

Colorectal cancer is a leading cause of cancer mortality despite recent expansion of treatment options in metastatic colorectal cancer (mCRC). Our knowledge about key signaling pathways in colorectal tumors has contributed to the identification of specific molecular markers of response to targeted agents. In this review we discuss well-established and potential predictive biomarkers of benefit with epidermal growth factor receptor (EGFR) inhibitors. Data derived from multiple phase III trials have indicated that KRAS mutations can be considered a highly specific negative biomarker of response to anti-EGFR monoclonal antibodies. Other molecular aberrations in pathways downstream of EGFR such as BRAF, NRAS, and PIK3CA mutations, and PTEN loss are also reviewed. Moreover biomarkers of efficacy to classic chemotherapeutic agents as well as recent advances regarding high-throughput technologies and circulating tumor cells are also considered. Personalized cancer medicine in the mCRC scenario seems to be near reality, but validation of many biomarkers in prospective clinical trials is urgently warranted.     

Predictive and prognostic biomarkers for targeted therapy in metastatic colorectal cancer

The use of targeted biologic agents in combination with chemotherapy has increased the overall survival (OS) of metastatic colorectal cancer (mCRC) to 23.5 months. With the assistance of Kirsten-ras (KRAS) mutational status, the subgroup population resistant to the inhibition of epidermal growth factor receptor (EGFR) by monoclonal antibodies (MoAbs) can be identified. However, only up to a third of the KRAS wild-type subpopulation respond to EGFR inhibition. Multiple factors, including relatively low response rates and high costs for targeted agents, are driving the search to identify further biomarkers within the EGFR/Ras/Raf/Mek/Erk and PTEN/PIP3/AKT signaling pathways. Vascular endothelial growth factor (VEGF) is a key player in tumor angiogenesis and the target for the MoAb bevacizumab, which is currently licensed for use in mCRC. Despite numerous studies, an equivalent predictive biomarker for bevacizumab has not been identified. Preclinical work indicates that inhibition of the insulin growth factor receptor (IGFR) pathway stops cellular transformation and tumor regression, thus identifying this pathway as a strong potential target for anticancer drug development and the identification of novel biomarkers. This review focuses on research relating to the roles of biomarkers within the EGF, VEGF, and IGF receptor pathways. The molecules KRAS, BRAF, NRAS, PTEN, PIP3, VEGF, IGF-1R, and IGF binding protein 3 are discussed. Currently, KRAS is the only biomarker used in clinical practice for mCRC. Pending the results of ongoing and future studies, additional biomarkers will be tested, tailoring our approach to targeted therapy in mCRC.     

Comparison of three distinct methods for the detection of circulating tumor cells in colorectal cancer patients

The detection of circulating tumor cells (CTCs) has considerable utility in the clinical management of patients with solid cancers. However, the phenotypic heterogeneity of CTCs and their low numbers in the bloodstream of patients means that no standardized detection method currently exists for these cells. This, together with differences in pre-analytical sample processing, has led to the collection and accumulation of inconsistent data among independent studies. Here, we compare the ability of three methods to detect CTCs in the blood of colorectal cancer patients. Specifically, different aliquots of the same blood sample were screened for the presence of CTCs by a multimarker RT-PCR assay, the standardized CellSearch assay and dHPLC-based gene mutation analysis. In the population tested, none of the blood samples analysed appeared to be positive by all three methods. Of the samples, 75% were positive for the presence of CTCs by the RT-PCR method. Only 20% were positive by the CellSearch assay, while 14.3% of samples displayed gene mutations consistent with the presence of CTCs when the dHPLC method was applied. The samples which were positive for CTCs by the CellSearch assay did not overlap with those that were positive by dHPLC. Interestingly, however, all of these samples were positive when assessed by RT-PCR. Conversely, of the samples that resulted negative by RT-PCR analysis, none appeared to be positive by either of the other methods. These data, therefore, indicate that of the three methods tested, the multimarker RT-PCR assay provides maximal probability of CTC detection. Here, we present the preliminary results of an ongoing clinical study. Future follow-up involving detection of CTCs in the blood of colorectal cancer patients using these three distinct methods will allow us to verify whether either a single method, or a combination of different assays, is necessary to uncover further prognostic significance of circulating tumor cells.     

Thymidylate synthase expression in circulating tumor cells: A new tool to predict 5‐fluorouracil resistance in metastatic colorectal cancer patients

Thymidylate synthase (TYMS) is an important enzyme for 5‐fluorouracil (5‐FU) metabolism in metastatic colorectal cancer (mCRC) patients. The search for this enzyme in circulating tumor cells (CTCs) can be a powerful tool to follow‐up cancer patients. mCRC patients were enrolled before the beginning of 5‐FU‐based chemotherapy. The blood was filtered on Isolation by Size of Epithelial Tumor Cells (ISET), and the analysis of TYMS expression in CTCs was made by immunocytochemistry. Additionally, we verified TYMS staining in primary tumors and metastases from the same patients. There were included 54 mCRC patients and 47 of them received 5‐FU‐based chemotherapy. The median CTCs number was 2 per mL. We were not able to analyze immunocytochemistry in 13 samples (9 patients with absence of CTCs and 4 samples due to technical reasons). Therefore, TYMS expression on CTCs was analyzed in 34 samples and was found positive in 9 (26.5%). Six of these patients had tumor progression after treatment with 5‐FU. We found an association between CTC TYMS staining and disease progression (DP), although without statistical significance (P = 0.07). TYMS staining in primary tumors and metastases tissues did not have any correlation with disease progression (P = 0.67 and P = 0.42 respectively). Patients who had CTC count above the median (2 CTCs/mL) showed more TYMS expression (P = 0.02) correlating with worse prognosis. Our results searching for TYMS staining in CTCs, primary tumors and metastases suggest that the analysis of TYMS can be useful tool as a 5‐FU resistance predictor biomarker if analyzed in CTCs from mCRC patients.     

New findings on primary and acquired resistance to anti-EGFR therapy in metastatic colorectal cancer: do all roads lead to RAS?

Anti-epidermal growth factor receptor therapy with the monoclonal antibodies cetuximab and panitumumab is the main targeted treatment to combine with standard chemotherapy for metastatic colorectal cancer. Many clinical studies have shown the benefit of the addition of these agents for patients without mutations in the EGFR pathway. Many biomarkers, including KRAS and NRAS mutations, BRAF mutations, PIK3CA mutations, PTEN loss, AREG and EREG expression, and HER-2 amplification have already been identified to select responders to anti-EGFR agents. Among these alterations KRAS and NRAS mutations are currently recognized as the best predictive factors for primary resistance. Liquid biopsy, which helps to isolate circulating tumor DNA, is an innovative method to study both primary and acquired resistance to anti-EGFR monoclonal antibodies. However, high-sensitivity techniques should be used to enable the identification of a wide set of gene mutations related to resistance.     

Therapeutic implications of resistance to molecular therapies in metastatic colorectal cancer

Metastatic colorectal cancer (mCRC) patients carrying KRAS mutated tumors do not benefit from epidermal growth factor receptor (EGFR)-targeted cetuximab- or panitumumab-based therapies. Indeed, the mutational status of KRAS is currently a validated predictive biomarker employed to select mCRC patients for EGFR targeted drugs. When patients fail standard 5-fluorouracil-, oxaliplatin-, irinotecan- and bevacizumab-based therapies, EGFR-targeted salvage therapy can be prescribed only for those individuals with KRAS wild-type cancer. Thus, clinicians are now facing the urgent issue of better understanding the biology of KRAS mutant disease, in order to devise novel effective therapies in such defined genetic setting. In addition to KRAS, recent data point out that BRAF and PIK3CA exon 20 mutations hamper response to EGFR-targeted treatment in mCRC, potentially excluding from treatment also patients with these molecular alterations in their tumor. This review will focus on current knowledge regarding the molecular landscape of mCRC including and beyond KRAS, and will summarize novel rationally-developed combinatorial regimens that are being evaluated in early clinical trials.     

Detection of KRAS mutations in circulating tumor cells from patients with metastatic colorectal cancer

Background: Quantification of Circulating Tumor Cells (CTCs) as a prognostic marker in metastatic colorectal cancer (mCRC) has already been validated and approved for routine use. However, more than quantification, qualification or characterization of CTCs is gaining importance, since the genetic characterization of CTCs may reflect, in a real time fashion, genetic profile of the disease. Objective: To characterize KRAS mutations (codon 12 and 13) in CTCs from patients with mCRC and to compare with matched primary tumor. Additionally, correlate these mutations with clinical and pathological features of patients. Methods: Blood samples were collected from 26 patients with mCRC from the AC Camargo Cancer Center (São Paulo-Brazil). CTCs were isolated by ISET technology (Isolation by Size of Epithelial Tumors; Rarecells Diagnostics, France) and mutations analyzes were performed by pyrosequencing (QIAGEN). Results: KRAS mutation was detected in 7 of the 21 cases (33%) of samples from CTCs. In matched primary tumors, 9 of the 24 cases (37.5%) were found KRAS mutated. We observed that 5 of the 9 samples with KRAS mutation in their primary tumor had also KRAS mutation in CTCs, meaning a concordance of 71% of matched cases (P = 0.017). KRAS mutation neither on primary tumor nor in CTCs was associated with clinical-pathological parameters analyzed. Conclusion: Faced with a polyclonal disease like colorectal cancer, which is often treated with alternating and successive lines of chemotherapy, real time genetic characterization of CTCs, in a fast and feasible fashion, can provide important information to clinical management of metastatic patients. Although our cohort was limited, it was possible to show a high grade of concordance between primary tumor and CTCs, which suggests that CTCs can be used as surrogate of primary tumors in clinical practice, when the knowledge of mutation profile is necessary and the primary tumor is not available.     

Circulating tumor cells in colorectal cancer: correlation with clinical and pathological variables.

BACKGROUND: The CellSearch System is a technique to detect circulating tumor cells (CTCs) in patients with cancer. Few data have been published concerning the role of CTCs detection by this method in colorectal cancer. The aim of this study was to correlate the presence of CTCs with the commonest clinical and morphological variables. PATIENTS AND METHODS: Blood samples were collected from 97 patients and 30 healthy volunteers. Quantification of CTCs in 7.5 ml of blood was carried out with the CellSearch System. The results were expressed as number of CTCs/7.5 ml and the cut-off of >or=2 CTCs/7.5 ml was chosen to define the test as positive. RESULTS: Positive CTCs were detected in 34 of 94 patients (36.2%). Correlation was not found among positive CTCs and location of primary tumor, increased carcinoembryonic antigen level, increased lactate dehydrogenase level or grade of differentiation. Only stage correlated with positive CTCs (20.7% in stage II, 24.1% in stage III and 60.7% in stage IV, P = 0.005). CONCLUSIONS: CTCs detection by CellSearch is a highly reproducible method that correlates with stage but not with other clinical and morphological variables in patients with colorectal cancer. Colon cancer tumor cells are detectable in all stages. Further studies are warranted.     

Non‐invasive sensitive detection of KRAS and BRAF mutation in circulating tumor cells of colorectal cancer patients

Characterization of genetic alterations in tumor biopsies serves as useful biomarkers in prognosis and treatment management. Circulating tumor cells (CTCs) obtained non‐invasively from peripheral blood could serve as a tumor proxy. Using a label‐free CTC enrichment strategy that we have established, we aimed to develop sensitive assays for qualitative assessment of tumor genotype in patients. Blood consecutively obtained from 44 patients with local and advanced colorectal cancer and 18 healthy donors were enriched for CTCs using a size‐based microsieve technology. To screen for CTC mutations, we established high‐resolution melt (HRM) and allele‐specific PCR (ASPCR) KRAS‐codon 12/13‐ and BRAF‐codon 600‐ specific assays, and compared the performance with pyrosequencing and Sanger sequencing. For each patient, the resulting CTC genotypes were compared with matched tumor and normal tissues. Both HRM and ASPCR could detect as low as 1.25% KRAS‐ or BRAF‐mutant alleles. HRM detected 14/44 (31.8%) patients with KRAS mutation in CTCs and 5/44 (11.3%) patients having BRAF mutation in CTCs. ASPCR detected KRAS and BRAF mutations in CTCs of 10/44 (22.7%) and 1/44 (2.3%) patients respectively. There was an increased detection of mutation in blood using these two methods. Comparing tumor tissues and CTCs mutation status using HRM, we observed 84.1% concordance in KRAS genotype (p = 0.000129, Fishers'' exact test; OR = 38.7, 95% CI = 4.05–369) and 90.9% (p = 0.174) concordance in BRAF genotype. Our results demonstrate that CTC enrichment, coupled with sensitive mutation detection methods, may allow rapid, sensitive and non‐invasive assessment of tumor genotype.     

The promise of liquid biopsy in cancer: a clinical perspective

The clinical utility of liquid biopsy in cancer treatment will increase as circulating tumor cells (CTCs) analysis move from the enumeration to the real-time measurement of tumor characteristics. Intratumor heterogeneity is becoming increasingly recognized as a major drawback to the shift to personalized medicine. Spatial and temporal heterogeneity might be reflected by the serial assessment of CTCs. Indeed, the developing technologies for CTCs analysis now allow digital genomic and next-generation sequencing approaches, able to differentiate molecular subtypes of the disease and to monitor genetic variation over time. The liquid biopsy of cancer might offer a real-time assessment of tumor biology, providing the opportunity to serially evaluate patients most likely to benefit from targeted drugs based on a dynamic characterization of the disease at the molecular level. Although hurdles remain before liquid biopsy is seen in routine clinical practice, the information derived from CTCs may facilitate the real-time identification of actionable mutations in cancer leading the way toward personalized medicine.     

Expected clinical applications of circulating tumor cells in breast cancer

Tumor cell invasion and intravascular filtration lead to the presence of circulating tumor cells (CTCs) in peripheral blood. CTCs have, thus, been counted in patients with cancer to analyze metastatic mechanisms or in the hope of developing clinical applications for diagnosis and therapy; various CTC-related studies have been performed. However, the clinical significance of CTCs remains to be established because of the extremely small number of CTCs in peripheral blood as compared with the number of blood cells. Technical problems (e.g. reproducibility and reliability) in the detection of CTCs also remain to be solved. The use of flow cytometric analysis, which can be performed with tumor-cell markers such as anti-epithelial cell adhesion molecule antibodies and anti-cytokeratin antibodies and non-tumor-cell markers such as anti-CD45 antibodies has enhanced specificity for the detection of tumor cells. The CellSearch System^® can detect 1 CTC in 7.5 mL of peripheral blood, with high reproducibility. Its detection rate and accuracy for CTCs have been confirmed. In the United States, clinical trials have used this system to detect CTCs in patients with metastatic breast cancer, metastatic colorectal cancer, and metastatic prostate cancer, and CTCs have been confirmed to be a useful prognostic factor. This system was also suggested to be useful for monitoring treatment response in patients with metastatic breast cancer and was approved by the United States Food and Drug Administration in 2004. Measuring CTC counts can facilitate the early prediction of treatment response and thereby avoid unnecessary therapy. CTCs may also be a useful biomarker for molecular targeted agents, enabling the identification of patients most likely to respond to a given treatment and facilitating treatment selection. However, the widespread use of CTC monitoring as a routine examination requires a further improvement in measurement sensitivity, the establishment of criteria for quantitative and qualitative evaluations, and additional clear-cut evidence supporting the clinical significance of CTCs. We expect that CTCs will be established to be a new diagnostic and therapeutic index for breast cancer.     

Concordant analysis of KRAS status in primary colon carcinoma and matched metastasis

KRAS somatic mutations are the main predictive factor for non response to EGFR-targeted monoclonal antibodies in metastatic colorectal cancer (mCRC) patients. We compared KRAS mutational status in the primary tumour and the corresponding metastases (1 to 4 sites) in 38 mCRC patients. KRAS mutational status was analysed using direct sequencing, SNAPShot multiplex PCR and Scorpion Taqman PCR analysis. Results showed 54% of primary tumours had KRAS mutations. A concordance of 97% between primaries and metastatic sites was observed. A tumour heterogeneity was also demonstrated in 5% of mCRC. One case with three different primary tumours harboured three different KRAS mutations, and only one was represented in the unique metastasis of this patient. We concluded there was a high concordance in the KRAS status between the primary tumour and metastases. More than one informative block and more sensitive assay may increase the accuracy of KRAS status determination.     

KRAS Testing and Its Importance in Colorectal Cancer

Cetuximab and panitumumab are monoclonal antibodies used in the treatment of metastatic colorectal cancer (mCRC) by selectively targeting the epidermal growth factor receptor (EGFR) axis. Studies have shown that mutations in codons 12/13 of exon 2 of the KRAS gene render these therapies ineffective. As a result, the National Comprehensive Cancer Network and American Society of Clinical Oncology recommend KRAS mutation testing in mCRC. Appropriate testing depends on the coordinated efforts of the entire treatment team, including the pathologist, who selects the tumor sample and testing platform as well as interprets and reports results. In addition to describing rationale and methodologies for KRAS mutation testing, the authors also summarize their algorithmic approach and elaborate the potential role of newer molecular biomarkers to predict anti-EGFR resistance in wild-type KRAS tumors.     

Apoptotic circulating tumor cells (CTCs) in the peripheral blood of metastatic colorectal cancer patients are associated with liver metastasis but not CTCs

Enumeration of circulating tumor cells (CTCs) by the CellSearch system provides prognostic information in metastatic colorectal cancer, regardless of metastatic site. We found that CTCs generally represent <1% of observed events with CellSearch analysis and adapted scoring criteria to classify other peripheral blood events. Examination of twenty two metastatic colorectal cancer patients'' blood revealed that patients with high CEA or liver metastases, but not lung or distant lymph node metastases, possessed significant numbers of apoptotic CTCs prior to treatment initiation by Fischer''s exact test. Six out of eleven patients with liver metastasis possessed apoptotic CTCs whereas one of nine patients with other metastases had measurable apoptotic CTCs. An elevated CTC number was not necessarily associated with apoptotic CTCs or CTC debris by Spearman''s correlation, suggesting the metastatic site rather than CTCs per se as contributing to the origin of these events.     

循环肿瘤细胞检测的临床有效性和实用性分析

循环肿瘤细胞(Circulating tumor cells,CTC)是一种特殊的可以作为诊断、预测多种肿瘤预后的生物标记物。目前,循环肿瘤细胞并未开始全面的临床应用,但关于循环肿瘤细胞的研究已经展示出较高的临床有效性,尤其是在乳腺癌、肺癌、前列腺癌及结直肠癌领域。本文综述了循环肿瘤细胞在转移癌和非转移癌的研究进展,并分析了循环肿瘤细胞的临床有效性和实用性。     

Distribution of KRAS and BRAF Mutations in Metastatic Colorectal Cancers in Turkish Patients

The results of this study demonstrate the potential prognostic and predictive values of KRAS and BRAF gene mutations in patients with colorectal cancer (CRC). It has been proven that KRAS and BRAF mutations are predictive biomarkers for resistance to anti-EGFR monoclonal antibody treatment in patients with metastatic CRC (mCRC). We demonstrated the distribution of KRAS (codons 12, 13 and 61) and BRAF (codon 600) gene mutations in 50 mCRCs using direct sequencing and compared the results with clinicopathological data. KRAS and BRAF mutations were identified in 15 (30%) and 1 (2%) patients, respectively. We identified KRAS mutations in codon 12, 13 and 61 in 73.3% (11/15), 20% (3/15) and 6.67% (1/15) of the positive patients, respectively. The KRAS mutation frequency was significantly higher in tumors located in the ascending colon (p=0.043). Thus, we found that approximately 1/3 of the patients with mCRC had KRAS mutations and the only clinicopathological factor related to this mutation was tumor location. Future studies with larger patient groups should yield more accurate data regarding the molecular mechanism of CRC and the association between KRAS and BRAF mutations and clinicopathological features.     

PIK3CA基因突变在结直肠癌中的研究进展

结直肠癌是较常见的恶性肿瘤,发病率在我国呈逐年上升趋势.肿瘤的发生是多因素、多阶段、多基因改变的结果,包括原癌基因的激活与抑癌基因的失活.PIK3 CA基因是近年发现的除KRAS突变之外的结直肠癌常见的突变基因,PI3K下游信号通路的异常活化在结直肠癌的发生过程中发挥着重要的作用.本文就PIK3CA基因的生物学作用,参与肿瘤不同阶段的发展,以及PIK3CA作为肿瘤标志物和分子靶点的潜在临床价值简要作一综述.