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.     

The Evolving Role of Circulating Tumor Cells in the Personalized Management of Breast Cancer: From Enumeration to Molecular Characterization

Circulating tumor cells (CTCs) represent tumor cells in the blood stream dislodged from the primary tumor. The presence of CTCs in the bloodstream provides a unique opportunity to sample cancer tissue by means of a relatively less-invasive “liquid biopsy.” Over the past decade, there has been a tremendous increase in the amount of research examining the potential clinical utility of CTCs in the management of cancer. A number of techniques to refine the sensitivity and range of CTC assays are also in development. In this article, we review the recent developments in the current and potential clinical applications of CTCs in breast cancer. CTC enumeration already has an established role as a prognostic biomarker in metastatic breast cancer, whereas molecular characterization of CTCs can serve as a potential predictive biomarker for therapy selection, pharmacodynamic evaluation, and identification of novel actionable targets for novel therapies. The role of CTCs in breast cancer screening and detection of recurrence is currently limited. Further development in techniques will be pivotal in enhancing the broad applicability of CTCs and advancing the field of personalized breast cancer therapy.     

Clinical significance of circulating tumor cells in breast cancer patients

Circulating tumor cells (CTCs) are defined as tumor cells circulating in the peripheral blood of patients, shed from either the primary tumors or its metastases. Many techniques have been developed in the recent years to identify CTCs in breast cancer patients, and trials have proved the prognostic significance of CTCs. In this study, we validated the CTC detection method of combining cell filtration and laser scanning cytometry (LSC), which was highly reproducible with increased sensitivity and accuracy. In 134 non-metastatic breast cancer patients analyzed, HER2 was found to be the only primary tumor characteristics that correlated with the presence of CTCs. 85 patients with definitive stage information were selected for association study between the disease stages and CTC numbers. The detection rate and the number of CTCs were correlated with the disease stages. Moreover, assessment of CTCs in 92 metastatic breast cancer patients was found to be able to predict the efficacy of chemotherapy. Increase in CTC numbers was an independent prognostic factor for treatment outcomes. Our results suggested that CTC assessment could be an indication of the disease progression and analysis of the properties of CTCs is likely to provide new insights into the biology of breast cancer and contribute to defining novel treatments and better prediction of clinical outcomes.     

Towards a personalized breast cancer treatment approach guided by circulating tumor cell (CTC) characteristics

Circulating tumor cells (CTCs) can be found in the peripheral blood of patients with different solid tumors, including breast cancer. A CTC count is a strong established prognostic factor in various stages in several tumor types. Besides that, characterization of CTCs is expected to become an invaluable tool to predict treatment response and personalize cancer treatments. Likely, CTCs are shed by different tumor lesions and may therefore provide a comprehensive view of tumor characteristics at a certain time-point, including inter- and intratumoral heterogeneity. Obtained through a simple venipuncture, CTCs could this way serve as a “liquid biopsy”. However, isolation and subsequent characterization of CTCs is technically extremely challenging, mainly due to the small number of cells amidst a large majority of leukocytes. A wide range of assays has been developed, but only the CellSearch System® (Veridex, Raritan, NJ, USA) has obtained FDA approval for CTC enumeration so far. For characterization purposes, no assay has been validated at all. Nevertheless, the first studies investigating the clinical value of CTC characteristics have been performed. Here, we review these clinical studies. The various techniques used to interrogate CTCs are briefly described and an overview of the clinical relevance of CTC characterization in breast cancer is given.     

Circulating tumors cells as biomarkers: progress toward biomarker qualification

Personalized cancer medicine requires the development of tumor-specific biomarkers to optimize selection of targeted therapies and to better assess response to therapy. Current efforts in several tumor types have shown that patients in whom circulating tumor cells (CTCs) are detected have an inferior prognosis relative to those in whom CTCs are not detected and that the elimination or decrease of CTCs following treatment is associated with improved clinical outcomes. Technological advances in the detection, isolation, capture, and characterization of CTCs from phlebotomy samples obtained in a routine clinical practice setting have enabled the evaluation of different CTC biomarkers. Unmet needs in cancer diagnosis and treatment where CTC biomarkers have been studied include determining prognosis, assessing the effects of treatment, and as a source of tumor for the biologic identification and characterization of determinants to predict sensitivity to one form of treatment versus another and to understand mechanisms of treatment resistance.At present, there is no single definition of a CTC and no single CTC "biomarker." Rather, multiple assays (tests) are in development for CTC biomarkers. However, before the role of any biomarker in medical decision making can be determined, it is essential that the assays used to measure the biomarker are analytically validated in a sequence of trials to generate the evidence to support the biomarker's use in the given context of use. It is against this background that this review focuses on the process of developing CTC biomarker assays, with the objective of outlining the necessary steps to qualify specific CTC tests for medical decision making in clinical practice or drug development. The potential for point-of-care tests is clear.     

Detection of circulating tumor cells is improved by drug-induced antigen up-regulation: preclinical and clinical studies

(51)Cr-prelabelled colon cancer cells (simulating 'circulating tumor cells', CTCs) were added to human peripheral blood and exposed to staurosporine (ST) to increase carcinoembryonic antigen (CEA) expression. CTCs were captured with immunomagnetic beads coated with Ber-EP4 monoclonal antibody, recognizing the common epithelial antigen present in the majority of cancer cells of epithelial origin, with capture efficiency of more than 80%. Moreover, ST treatment increased CEA expression without compromising Ber-EP4 capture efficiency. In a pilot clinical study on 37 patients, CTCs were captured using Ber-EP4 beads, and recognized by RT-PCR set for CEA or cytokeratin-19 (CK) mRNA detection. The results showed that: (a) the percentage of CEA-positive CTCs (CTC(CEA), 54.1%) was lower than that of CK-positive CTCs (CTC(CK), 70.3%); (b) in vitro ST treatment converted a significant number of CTC(CEA)-negative into CTC(CEA)-positive cases. Therefore, immunomagnetic capture combined with exposure to ST provides a feasible and sensitive technique for the detection of functionally-active CTCs responsive to ST-mediated CEA up-regulation.     

Significance of circulating tumor cells in the portal vein regarding metastases and vascular invasion in hepatocellular carcinoma patients

BackgroundVascular invasion is an important risk factor of poor prognosis in hepatocellular carcinoma (HCC) patients. The detection of circulating tumor cells (CTCs) in the blood is direct evidence of tumor presence. There are few reports on CTCs and metastasis and vascular invasion of HCC. The purpose of this study was to analyze the significance of CTCs in the portal vein regarding metastases and vascular invasion in HCC patients.MethodsA total of 104 HCC patients diagnosed and treated in Zhengzhou University People’s Hospital were enrolled. Surgery was performed in 60 individuals. Portal vein blood samples were collected before treatment for CTCs detection. We used the isolation by size of epithelial tumor cells (ISET) and fluorescence in situ hybridization (FISH) to enrich and classify CTCs from blood samples. The patients were divided into metastasis and nonmetastasis groups according to the metastasis status before treatment. Differences in clinical indicators such as alpha-fetoprotein (AFP) levels, tumor size, CTCs count, and macrovascular tumor thrombus between the two groups were analyzed as well as the associations of CTCs count with the above indicators. For individuals with postoperative pathology, the relationship between CTCs counts and microvascular invasion (MVI) was analyzed.ResultsThe amounts of portal vein CTCs were higher in patients with metastases compared with the nonmetastases group (20 vs. 7; z=3.795; P<0.001). Multivariate logistic regression analysis showed that the CTC count was a risk factor for HCC metastasis [odds ratio (OR) =1.044; 95% CI: 1.011–1.079]. The sensitivity and specificity of CTC count in predicting HCC metastasis were 82.93% and 52.38%, respectively. CTC count was significantly correlated with tumor size (r_s=0.308; P=0.001), vascular invasion (z=4.211; P<0.001), and MVI (z=12.763; P=0.002). A threshold CTC count of seven showed the most significant power for predicting metastasis.ConclusionsVascular invasion positivity was closely related to HCC metastasis. Portal vein CTC count before treatment was correlated with vascular invasion and could be considered one of the factors affecting HCC metastasis. However, the ability of CTC count was limited in predicting HCC metastasis due to insufficient specificity.     

非小细胞肺癌循环肿瘤细胞检测进展

肺癌是世界范围内发病率最高的恶性肿瘤, 约有18%的癌症相关死亡与肺癌有关。循环肿瘤细胞(CTCs)的出现可看做是肿瘤细胞播散入血的直接体现, 而这正是导致非小细胞肺癌患者预后较差的最重要因素之一。检测外周血中循环肿瘤细胞有望成为诊断肺癌的辅助方法, 使肺癌患者得到最佳的个体化治疗。研究者们已尝试多种不同的方法从外周血中分离CTCs。虽然有关CTCs检测的研究众多, 但不同检测方法的敏感度、特异性及重复性限制了其临床意义, 本文就现有的各项技术进行综述。      

Determination of cut-offs for circulating tumor cell measurement in metastatic cancer

The metastatic transformation of epithelial tumors progresses through various steps leading to the generation of circulating tumor cells (CTCs). Measurement of CTCs in the peripheral blood is being increasingly recognized as a promising tool in breast oncology. Several studies have evaluated the prognostic significance of CTCs in newly diagnosed metastatic breast cancer (MBC) patients. The IC 2006-04 was a high-powered, prospective, multicenter, observational study conceived to assess CTC changes in women with MBC treated with first-line chemotherapy. Levels ≥ 5 CTCs/7.5 ml blood at baseline and before the second cycle of treatment were independent prognostic factors associated with shorter progression-free and overall survival. This study provides further level II evidence for the clinical and prognostic value of CTCs in MBC, confirming data from earlier small studies. It also provides proof that CTCs should be investigated in ongoing interventional trials to see if better patient outcomes can be attained by altering treatment based on CTC levels.     

Role of Circulating Tumor Cells in Metastatic Colorectal Cancer: Clinical Challenges and Opportunities

Circulating tumour cells (CTCs) have been presumed critical to the metastatic process since 1800. These epithelial cells are disseminated from the primary or metastatic tumor site and can be identified in the peripheral blood of patients. Nowadays, technical advances have rendered it easier to reproducibly and repeatedly sample this population of cells with an acceptable degree of accuracy. Therefore, these cells could become an attractive surrogate for phenotypic and genotypic markers in correlation with the development of molecular targeted therapies. In metastatic colorectal cancer several prospective studies have demonstrated the independent prognostic significance of CTCs and identified the number of CTCs before and during treatment as a predictor for overall survival and disease free survival. However, the underlying molecular characteristics of CTCs associated with outcome remain largely unknown. In this review, the role of CTCs in metastatic colorectal cancer is discussed. The variety of assays that can be used for enrichment and detection steps in CTC detection will be described and the clinical utility of these cells for assessing prognosis and monitoring response to therapy will be analyzed. We will also address the shortcomings of current detection methods that fail to identify a mesenchymal subgroup of CTCs, and briefly address how characterization of these cells can help elucidate the biology of cancer metastases.     

Circulating tumour cells as tumour biomarkers in melanoma: detection methods and clinical relevance

Circulating tumour cells (CTCs) are cells of solid tumour origin detectable in the peripheral blood. Their occurrence is considered a prerequisite step for establishing distant metastases. Metastatic melanoma was the first malignancy in which CTCs were detected and numerous studies have been published on CTC detection in melanoma at various stages of disease. In spite of this, there is no general consensus as to the clinical utility of CTCs in melanoma, largely due to conflicting results from heterogeneous studies and discrepancies in methods of detection between studies. In this review, we examine the possible clinical significance of CTCs in cutaneous, mucosal and ocular melanoma, focusing on detection methods and prognostic value of CTC detection.     

Detection of circulating tumor cells in peripheral blood of heavily treated metastatic breast cancer patients

Background

Circulating tumor cells (CTCs) are detected in peripheral blood of breast cancer patients, and they may play an important role as a prognostic and predictive marker. We conducted this study to determine the presence of CTCs with the CellSearch System? and the clinical significance in treatment of metastatic breast cancer (MBC).

Method

Twenty-eight MBC patients were enrolled. These patients were followed by assessing CTCs, imaging studies, and serum tumor markers. Blood samples were collected before starting a new treatment and at the treatment evaluation period (2–3 months after starting chemotherapy). The cutoff for CTC level was 5.

Results

At baseline, 9 of 28 patients (32%) had ≥5 CTCs per 7.5 mL of blood. At the evaluation period, 5 of 23 patients (22%) had ≥5 CTCs. The baseline CTC number did not contribute to determine their overall survival (OS); however, CTCs at the evaluation period were available to predict their OS (p < 0.001). In two cases, both CTCs and tumor markers were available as predictors of treatment efficacy. In two other cases, although alterations of tumor markers might not reflect disease condition, CTC alteration corresponded to their condition. One patient who had multiple skeletal metastasis only, experienced a decrease in her CTCs in spite of tumor marker alteration.

Conclusions

We suggest that monitoring the number of CTCs may be helpful in predicting the efficacy of the treatment and the prognosis. CTCs might be especially useful with patients whose lesions are difficult to assess.     

A higher number of circulating tumor cells (CTC) in peripheral blood indicates poor prognosis in prostate cancer patients--a meta-analysis

Objective: The prevalence of prostate cancer (PCa) is high and PCa is the most common cutaneous cancer in men worldwide. Despite extensive research efforts, very few biomarkers of PCa have been introduced to date in clinical practice. A meta-analysis was performed on the most recently reported CTC to assess its prognostic effect and to elucidate whether its detection in the peripheral blood of patients diagnosed with metastatic, castration-resistant prostate cancer (CPRC) and Hormone Refractory Prostate Cancer (HRPC) can be used as a prognostic factor for survival. Methods: We searched Science Direct, EMBASE, PubMed, and Cell Research databases for studies that assessed the prognostic relevance of the presence number of circulating tumor cells (CTC) detection in the peripheral blood (PB). A fixed effects model with relative risk (RR) and 95% confidence interval (95% CI) is used for analysis. Results: A total of 4 studies, including 486 patients, were eligible for final analysis. Pooled analysis indicated the presence number of CTC per 7.5 ml peripheral blood is associated with a poor survival rate (RR=2.51, 95% CI 1.96-3.21). Conclusion: The unfavorable count (presence of 5 or more CTCs per 7.5 ml peripheral blood) was associated with poor overall survival in patients with PCa. CTC counts can be used as an accurate and independent predictor of survival rate in patients with PCa.     

微流控芯技术检测循环肿瘤细胞在脑胶质瘤预后预测中的价值

背景与目的：脑胶质瘤患者的预后既往多通过生化指标进行预测,临床实践中有一定难度且受多种因素影响,导致预测效率相对较差。探讨微流控芯技术检测循环肿瘤细胞（circulating tumor cell,CTC）在脑胶质瘤预后预测中的价值。方法：选取2016年3月—2020年3月内蒙古自治区人民医院神经外科收治的96例脑胶质瘤患者为研究对象,采用微流控芯技术富集患者外周血CTC,并利用免疫荧光法对CTC进行鉴定;采用logistic回归方程分析脑胶质瘤患者外周血CTC的检测结果与脑胶质瘤临床特征之间的关系并建立受试者工作特征（receiver operating characteristic,ROC）曲线;制作并分析脑胶质瘤患者术后生存曲线。结果：微流控芯技术对CTC富集联合免疫荧光结果显示,CTC检测阳性率为42.71%,外周血检测出的CTC数目为（66.27±6.36）/mL;单因素分析结果显示,外周血CTC与患者的肿瘤分期、组织学类型、淋巴结转移是否存在囊性病变、神经元特异性烯醇化酶（neuron-specific enolase,NSE）密切相关（P<0.05）,与年龄、性别、KPS评分、血清胶质纤维酸性蛋白（glial fibrillary acidic protein,GFAP）含量等临床特征无相关性;多因素分析结果显示肿瘤分期、组织学类型及NSE的表达与CTC密切相关;通过ROC曲线分析得出肿瘤分期、组织学类型以及NSE的AUC分别为0.645、0.687、0.720,预测概率AUC为0.814（P<0.05）;CTC阳性组和阴性组患者1年生存率差异无统计学意义（P>0.05）,但两组患者2年和3年生存率差异有统计学意义（P<0.05）。结论：微流控芯技术可定量检测脑胶质瘤患者外周血CTC,其水平与肿瘤分期、组织学类型、NSE密切相关,直接影响脑胶质瘤患者远期生存率。因此,外周血CTC可作为脑胶质瘤患者预后预测的重要指标。     

Circulating tumor cells in pancreatic cancer patients: Methods of detection and clinical implications

The poor prognosis of pancreatic cancer patients is associated with the frequent and early dissemination of the disease, as well as late detection due to unspecific and late symptoms from the primary tumor. Pancreatic cancers frequently spread to the liver, lung and skeletal system, suggesting that pancreatic tumor cells must be able to intravasate and travel through the circulation to distant organs. Circulating tumor cells (CTCs) are tumor cells that have acquired the ability to enter the circulatory system; this cell population is ultimately responsible for the development of metastases in distant organs. Clinical studies have revealed that the presence of CTCs in blood is correlated with disease progression for other cancers, such as breast, colorectal and prostate cancer. However, as CTCs are extremely rare, both enrichment and sensitive methods of detection are required for their enumeration. This review highlights various enrichment procedures and methods for the detection of CTCs. Furthermore, we systematically review previously reported studies of the clinical relevance of CTC detection in pancreatic cancer patients. There is evidence that the presence of CTCs also correlates with an unfavorable outcome in pancreatic cancer patients. However, technical/methodological issues may explain why some studies only show a trend toward an association between CTC detection and disease progression. Larger studies, as well as characterization of the CTC population, are required to achieve further insight into the clinical implications of CTC detection in pancreatic cancer patients.     

Circulating tumor cells as pharmacodynamic biomarker in early clinical oncological trials

Circulating tumor cells (CTCs) have received a lot of attention from both researchers and clinicians because of their prognostic value for progression-free and overall survival in selected tumor types. CTCs are readily available by single venipuncture, thereby posing little burden on the patient and allowing for repeated, sequential sampling during therapy. Nowadays, the sensitivity of several CTC detection and capture techniques allow for further characterization and analysis of specific targets of interest on the CTC itself. These techniques have given CTCs the potential to be used as a pharmacodynamic read-out in drug development. In this review, we explore the utility of CTCs as a pharmacodynamic biomarker in early clinical oncological trials. We present an overview of current literature on assays for CTCs as pharmacodynamic biomarker, their different targets of interest and their level of validation, followed by discussion of their limitations.     

Quantitation of circulating tumor cells in blood samples from ovarian and prostate cancer patients using tumor-specific fluorescent ligands

Quantitation of circulating tumor cells (CTCs) can provide information on the stage of a malignancy, onset of disease progression and response to therapy. In an effort to more accurately quantitate CTCs, we have synthesized fluorescent conjugates of 2 high-affinity tumor-specific ligands (folate-AlexaFluor 488 and DUPA-FITC) that bind tumor cells >20-fold more efficiently than fluorescent antibodies. Here we determine whether these tumor-specific dyes can be exploited for quantitation of CTCs in peripheral blood samples from cancer patients. A CTC-enriched fraction was isolated from the peripheral blood of ovarian and prostate cancer patients by an optimized density gradient centrifugation protocol and labeled with the aforementioned fluorescent ligands. CTCs were then quantitated by flow cytometry. CTCs were detected in 18 of 20 ovarian cancer patients (mean 222 CTCs/ml; median 15 CTCs/ml; maximum 3,118 CTCs/ml), whereas CTC numbers in 16 gender-matched normal volunteers were negligible (mean 0.4 CTCs/ml; median 0.3 CTCs/ml; maximum 1.5 CTCs/ml; p < 0.001, chi(2)). CTCs were also detected in 10 of 13 prostate cancer patients (mean 26 CTCs/ml, median 14 CTCs/ml, maximum 94 CTCs/ml) but not in 18 gender-matched healthy donors (mean 0.8 CTCs/ml, median 1, maximum 3 CTC/ml; p < 0.0026, chi(2)). Tumor-specific fluorescent antibodies were much less efficient in quantitating CTCs because of their lower CTC labeling efficiency. Use of tumor-specific fluorescent ligands to label CTCs in peripheral blood can provide a simple, accurate and sensitive method for determining the number of cancer cells circulating in the bloodstream.     

Molecular characterization of circulating tumor cells in breast cancer: challenges and promises for individualized cancer treatment

Blood testing using Circulating Tumor Cells (CTCs) has emerged as one of the hottest fields in cancer diagnosis. Research on CTCs present nowadays a challenge, as these cells are well defined targets for understanding tumour biology and improving cancer treatment. The presence of tumor cells in patient’s bone marrow or peripheral blood is an early indicator of metastasis and may signal tumor spread sooner than clinical symptoms appear and imaging results confirm a poor prognosis. CTC enumeration can serve as a “liquid biopsy” and an early marker to assess response to systemic therapy. Definition of biomarkers based on comprehensive characterization of CTCs has a strong potential to be translated to individualized targeted treatments and spare breast cancer patients unnecessary and ineffective therapies but also to reduce the costs for the health system and to downsize the extent and length of clinical studies. In this review, we briefly summarize recent studies on the molecular characterization of circulating tumor cells in breast cancer and discuss challenges and promises of CTCs for individualized cancer treatment.     

Identifying cancer origin using circulating tumor cells

Circulating tumor cells (CTCs) have become an established clinical evaluation biomarker. CTC count provides a good correlation with the prognosis of cancer patients, but has only been used with known cancer patients, and has been unable to predict the origin of the CTCs. This study demonstrates the analysis of CTCs for the identification of their primary cancer source. Twelve mL blood samples were equally dispensed on 6 CMx chips, microfluidic chips coated with an anti-EpCAM-conjugated supported lipid bilayer, for CTC capture and isolation. Captured CTCs were eluted to an immunofluorescence (IF) staining panel consisting of 6 groups of antibodies: anti-panCK, anti-CK18, anti-CK7, anti-TTF-1, anti-CK20/anti-CDX2, and anti-PSA/anti-PSMA. Cancer cell lines of lung (H1975), colorectal (DLD-1, HCT-116), and prostate (PC3, DU145, LNCaP) were selected to establish the sensitivity and specificity for distinguishing CTCs from lung, colorectal, and prostate cancer. Spiking experiments performed in 2mL of culture medium or whole blood proved the CMx platform can enumerate cancer cells of lung, colorectal, and prostate. The IF panel was tested on blood samples from lung cancer patients (n = 3), colorectal cancer patients (n = 5), prostate cancer patients (n = 5), and healthy individuals (n = 12). Peripheral blood samples found panCK⁺ and CK18⁺ CTCs in lung, colorectal, and prostate cancers. CTCs expressing CK7⁺ or TTF-1⁺, (CK20/ CDX2)⁺, or (PSA/ PSMA)⁺ corresponded to lung, colorectal, or prostate cancer, respectively. In conclusion, we have designed an immunofluorescence staining panel to identify CTCs in peripheral blood to correctly identify cancer cell origin.