Expression of truncated human epidermal growth factor receptor 2 on circulating tumor cells of breast cancer patients

Circulating tumor cells: from new biological insights to clinical practice

The primary reason for high mortality rates among cancer patients is metastasis, where tumor cells migrate through the bloodstream from the original site to other parts of the body. Recent advancements in technology have significantly enhanced our comprehension of the mechanisms behind the bloodborne spread of circulating tumor cells (CTCs). One critical process, DNA methylation, regulates gene expression and chromosome stability, thus maintaining dynamic equilibrium in the body. Global hypomethylation and locus-specific hypermethylation are examples of changes in DNA methylation patterns that are pivotal to carcinogenesis. This comprehensive review first provides an overview of the various processes that contribute to the formation of CTCs, including epithelial-mesenchymal transition (EMT), immune surveillance, and colonization. We then conduct an in-depth analysis of how modifications in DNA methylation within CTCs impact each of these critical stages during CTC dissemination. Furthermore, we explored potential clinical implications of changes in DNA methylation in CTCs for patients with cancer. By understanding these epigenetic modifications, we can gain insights into the metastatic process and identify new biomarkers for early detection, prognosis, and targeted therapies. This review aims to bridge the gap between basic research and clinical application, highlighting the significance of DNA methylation in the context of cancer metastasis and offering new avenues for improving patient outcomes.

Transferrin receptor-based circulating tumor cell enrichment provides a snapshot of the molecular landscape of solid tumors and correlates with clinical outcomes

Circulating tumor cells (CTCs) captured from the bloodstream of patients with solid tumors have the potential to accelerate precision oncology by providing insight into tumor biology, disease progression and response to treatment. However, their potential is hampered by the lack of standardized CTC enrichment platforms across tumor types. EpCAM-based CTC enrichment, the most commonly used platform, is limited by EpCAM downregulation during metastasis and the low EpCAM expression in certain tumor types, including the highly prevalent and lethal NSCLC. In this study we demonstrate that Transferrin Receptor (TfR) is a selective, efficient biomarker for CTC identification and capture in patients with prostate, pancreatic and NSCLC. TfR identifies significantly higher CTC counts than EpCAM, and TfR + -CTC enumeration correlates with disease progression in metastatic prostate and pancreatic cancers, and overall survival and osimetrinib-resistance in non-small cell lung cancer (NSCLC). Profiling of TfR + -CTCs provides a snapshot of the molecular landscape of each respective tumor type and identifies potential mechanisms underlying treatment response to EGFR TKi and immune checkpoint inhibitors in NSCLC.

One sentence summary

Transferrin Receptor identifies circulating tumor cells in solid tumors.

Clinical Impact of New Treatment Strategies for HER2-Positive Metastatic Breast Cancer Patients with Resistance to Classical Anti-HER Therapies

HER2-positive breast cancer accounts for 15-20% of all breast cancer cases. This subtype is characterized by an aggressive behavior and poor prognosis. Anti-HER2 therapies have considerably improved the natural course of the disease. Despite this, relapse still occurs in around 20% of patients due to primary or acquired treatment resistance, and metastasis remains an incurable disease. This article reviews the main mechanisms underlying resistance to anti-HER2 treatments, focusing on newer HER2-targeted therapies. The progress in anti-HER2 drugs includes the development of novel antibody-drug conjugates with improvements in the conjugation process and novel linkers and payloads. Moreover, trastuzumab deruxtecan has enhanced the efficacy of trastuzumab emtansine, and the new drug trastuzumab duocarmazine is currently undergoing clinical trials to assess its effect. The combination of anti-HER2 agents with other drugs is also being evaluated. The addition of immunotherapy checkpoint inhibitors shows some benefit in a subset of patients, indicating the need for useful biomarkers to properly stratify patients. Besides, CDK4/6 and tyrosine kinase inhibitors are also included in the design of new treatment strategies. Lapitinib, neratinib and tucatinib have been approved for HER2-positive metastasis patients, however clinical trials are currently ongoing to optimize combined strategies, to reduce toxicity, and to better define the useful setting. Clinical research should be strengthened along with the discovery and validation of new biomarkers, as well as a deeper understanding of drug resistance and action mechanisms.

Comprehensive liquid biopsy analysis as a tool for the early detection of minimal residual disease in breast cancer

Liquid biopsy (LB) provides a unique minimally invasive tool to follow-up cancer patients over time, to detect minimal residual disease (MRD), to study metastasis-biology and mechanisms of therapy-resistance. Molecular characterization of CTCs offers additionally the potential to understand resistance to therapy and implement individualized targeted treatments which can be modified during the disease evolution and follow-up period of a patient. In this study, we present a long-term follow-up of operable breast cancer patients based on a comprehensive liquid biopsy analysis. We performed a comprehensive liquid biopsy analysis in peripheral blood of 13 patients with early-stage operable breast cancer at several time points for a period of ten years, consisting of: (a) CTC enumeration using the CellSearch system, (b) phenotypic analysis of CTCs using Immunofluorescence, (c) gene expression analysis, in EpCAM(+) CTCs for CK-19, CD24,CD44, ALDH1, and TWIST1, (d) analysis of PIK3CA and ESR1 mutations in EpCAM(+) CTCs and corresponding plasma ctDNA and (e) DNA methylation of ESR1 in CTCs. 10/13 (77%) patients were found negative for LB markers in PB during the whole follow-up period, and these patients did not relapse during the follow-up. However, 3/13(18%) patients that were positive for at least one LB marker relapsed within the follow-up period. The molecular characteristics of CTCs were highly different even for the same patient at different time points, and always increased before the clinical relapse. Our results indicate that liquid biopsy can reveal the presence of MRD at least 4 years before the appearance of clinically detectable metastatic disease demonstrating that a comprehensive liquid biopsy analysis provides highly important information for the therapeutic management of breast cancer patients.

TLR4 and pSTAT3 Expression on Circulating Tumor Cells (CTCs) and Immune Cells in the Peripheral Blood of Breast Cancer Patients: Prognostic Implications

TLR4 and pSTAT3 are key players in cancer inflammation and immune evasion; however, their role in the peripheral blood (PB) is largely unexplored. Herein we evaluated their expression in the circulating tumor cells (CTCs) and peripheral-blood mononuclear cells (PBMCs) of patients with early (n = 99) and metastatic (n = 100) breast cancer (BC). PB samples obtained prior to adjuvant and first-line therapy, were immunofluorescently stained for Cytokeratins/TLR4/pSTAT3/DAPI and analyzed via Ariol microscopy. TLR4+ CTCs were detected in 50% and 68% of early and metastatic CTC-positive patients, respectively, and pSTAT3+ CTCs in 83% and 68%, respectively. In metastatic patients, CTC detection was associated with a high risk of death (HR: 1.764, p = 0.038), while TLR4+ CTCs correlated with a high risk of disease progression (HR: 1.964, p = 0.030). Regarding PBMCs, TLR4 expression prevailed in metastatic disease (p = 0.029), while pSTAT3 expression was more frequent in early disease (p = 0.014). In early BC, TLR4 expression on PBMCs independently predicted for high risk of relapse (HR: 3.549; p = 0.009), whereas in metastatic BC, TLR4+/pSTAT3- PBMCs independently predicted for high risk of death (HR: 2.925; p = 0.012). These results suggest that TLR4/pSTAT3 signaling on tumor- and immune-cell compartments in the PB could play a role in BC progression, and may hold independent prognostic implications for BC patients.

Circulating non-coding RNAs as a diagnostic and management biomarker for breast cancer: current insights

Cancer biomarkers can be used to determine the molecular status of a tumor or its metastases, which either release them directly into body fluids or indirectly through disruption of tumor/metastatic tissue. New minimally invasive and repeatable sample collection methods, such as liquid biopsy, have been developed in the last decade to apply cancer knowledge and track its progression. Circulating non-coding RNAs, which include microRNAs, long non-coding RNAs, and PIWI-interacting RNAs, are increasingly being recognized as potential cancer biomarkers. The growing understanding of cancer's molecular pathogenesis, combined with the rapid development of new molecular techniques, encourages the study of early molecular alterations associated with cancer development in body fluids. Specific genetic and epigenetic changes in circulating free RNA (cf-RNA) in plasma, serum, and urine could be used as diagnostic biomarkers for a variety of cancers. Only a subset of these cf-RNAs have been studied in breast cancer, with the most extensive research focusing on cf-miRNA in plasma. These findings pave the way for immediate use of selected cf-RNAs as biomarkers in breast cancer liquid biopsy, as well as additional research into other cf-RNAs to advance.

Circulating tumor cells as prognostic biomarkers in breast cancer: current status and future prospects

Introduction : Despite advances in diagnostic and therapeutic techniques breast cancer is still associated with significant morbidity and mortality. CTCs play a crucial role in the metastatic process, which is the main cause of death in BC patients.Areas covered : This review discusses the prognostic and predictive value of CTCs and their prospective in management of BC patients.Expert opinion : The analysis of CTCs through improved technologies offers a new insight into the metastatic cascade. Assessment of the number and molecular profile of CTCs holds great promises for disease monitoring and therapeutic decisions. However, more research is needed until they can be used in therapeutic decisions in clinical practice.

RNA-Based CTC Analysis Provides Prognostic Information in Metastatic Breast Cancer

In metastatic breast cancer (MBC) the molecular characterization of circulating tumor cells (CTCs) provides a unique tool to understand metastasis-biology and therapy-resistance. We evaluated the prognostic significance of gene expression in EpCAM⁽⁺⁾ CTCs in 46 MBC patients based on a long follow-up. We selected a panel consisting of stem cell markers (CD24, CD44, ALDH1), the mesenchymal marker TWIST1, receptors (ESR1, PGR, HER2, EGFR) and the epithelial marker CK-19. Singleplex RT-qPCR was used for TWIST1 and CK-19 and multiplex RT-qPCR for stem cell markers and receptors. A group of 19 healthy donors (HD) was used as control. Univariate (p = 0.001) and multivariate analysis (p = 0.002) revealed the prognostic value of combined gene expression of CK-19(+), CD44^high/CD24^low, ALDH1^high/CD24^low and HER2 over-expression for overall survival (OS). The Kaplan–Meier estimates of OS were significantly different in patients positive for CK-19 (p = 0.028), CD44^high/CD24^low (p = 0.002), ALDH1^high/CD24^low (p = 0.007) and HER2-positive (p = 0.022). Our results indicate that combined gene expression analysis in EpCAM⁽⁺⁾ CTCs provides prognostic information in MBC.

Combining losartan with radiotherapy increases tumor control and inhibits lung metastases from a HER2/neu-positive orthotopic breast cancer model

BACKGROUND

Patients with metastatic HER2/neu-positive (HER2/neu +) breast cancer (BC) often experience treatment resistance, disease recurrences and metastases. Thus, new approaches for improving the treatment of HER2/neu + BC to prevent metastatic dissemination are urgently needed. Our previous studies have shown that losartan, an angiotensin receptor blocker, increases tumor perfusion and decreases hypoxia in a number of tumor models. Hypoxia reduces the efficacy of radiation and increases metastases. We therefore hypothesized that by modifying tumor stroma and increasing oxygenation, losartan will improve the outcome of radiotherapy and inhibit disease progression in a highly metastatic HER2/neu + murine BC model.

METHODS

We established a metastatic HER2/neu + murine BC line (MCa-M3C) and used it to generate mammary fat pad isografts in syngeneic female FVB/N mice. Starting on day 3 after orthotopic tumor implantation, we administered a 7-day losartan treatment (40 mg/kg BW, gavage daily); or a 7-day losartan treatment followed by 20 Gy single dose local irradiation (S-IR) on day 10 (tumor size ~ 100 mm3), or 20 Gy local fractionated (5 × 4 Gy daily) irradiation (F-IR) on days 10-14. We analyzed tumor-growth delay (TGD), development of spontaneous lung metastases, animal survival, tumor vascular density, and tumor hypoxia.

RESULTS

Treatments with S-IR, F-IR, Losartan + S-IR, or Losartan + F-IR resulted in a significantly increased TGD (8-16 days) in MCa-M3C tumors versus controls. However, the combination of Losartan + S-IR and Losartan + F-IR further enhanced tumor response to radiation alone by increasing TGD an additional 5 to 8 days for both single and fractionated dose irradiation (P < 0.01), decreasing lung metastasis (Losartan + IR vs. Control, P < 0.025), and increasing animal survival (Losartan + IR vs. Control, P = 0.0303). In addition, losartan treatment significantly increased tumor vascularity (P = 0.0314) and decreased pimonidazole positive (hypoxic) area (P = 0.0002).

CONCLUSIONS

Combining losartan with local irradiation significantly enhanced tumor response, at least in part via reduced tumor hypoxia presumably due to increased tumor perfusion. Our findings suggest that combining losartan with radiotherapy is a potential new treatment strategy for local control and inhibiting metastasis in HER2 + BC.

Role of inflammatory microenvironment: potential implications for improved breast cancer nano-targeted therapy

Tumor cells, inflammatory cells and chemical factors work together to mediate complex signaling networks, which forms inflammatory tumor microenvironment (TME). The development of breast cancer is closely related to the functional activities of TME. This review introduces the origins of cancer-related chronic inflammation and the main constituents of inflammatory microenvironment. Inflammatory microenvironment plays an important role in breast cancer growth, metastasis, drug resistance and angiogenesis through multifactorial mechanisms. It is suggested that inflammatory microenvironment contributes to providing possible mechanisms of drug action and modes of drug transport for anti-cancer treatment. Nano-drug delivery system (NDDS) becomes a popular topic for optimizing the design of tumor targeting drugs. It is seen that with the development of therapeutic approaches, NDDS can be used to achieve drug-targeted delivery well across the biological barriers and into cells, resulting in superior bioavailability, drug dose reduction as well as off-target side effect elimination. This paper focuses on the review of modulation mechanisms of inflammatory microenvironment and combination with nano-targeted therapeutic strategies, providing a comprehensive basis for further research on breast cancer prevention and control.

Dynamic changes of CTCs in patients with metastatic HR(+)/HER2(-) breast cancer receiving salvage treatment with everolimus/exemestane

PURPOSE

Detection of CTCs represents a poor prognostic factor in patients with early and metastatic breast cancer (mBC) and treatment with everolimus-exemestane (E/E) is an established effective treatment in hormone receptor-positive/HER2-negative mBC patients. The effect of E/E on CTCs in mBC patients was prospectively investigated.

METHODS

CTCs from 50 pre-treated patients with mBC receiving E/E were analyzed using the CellSearch (CS) platform and triple immunofluorescence (IF) staining for cytokeratin, M30 and Ki67 expression to assess their proliferative and apoptotic status.

RESULTS

CTCs (by CS) were detected in 64% of patients before treatment and E/E administration resulted in their decreased prevalence [(n = 18; 36%, p = 0.004) and (n = 7; 19.4%, p = 0.019) post-1st and post-3rd treatment cycle, respectively] whereas it was significantly increased at disease progression (PD: 61%) compared to post-1st and post-3rd cycle (p = 0.049 and p = 0.021, respectively). Ki67-positive CTCs were detected in 60%, 60%, 17% and 50% of patients before treatment, post-1st, post-3rd cycle and at PD, respectively, while the opposite was observed for M30-positive CTCs (0% at baseline, 10% after the 1st cycle, 50% after the 3rd cycle and 0% at PD). The detection of even ≥ 1 CTC/5 ml after one cycle was associated with decreased PFS (3.3 vs 9.0 months, p = 0.025) whereas the detection of even ≥ 2 CTCs at PD was associated with decreased OS (32.4 vs 19.5 months; p = 0.009).

CONCLUSIONS

The combination of E/E resulted in early elimination of proliferating CTCs in mBC patients and this effect was associated with a favorable clinical outcome.

Molecular characterization of circulating tumour cells identifies predictive markers for outcome in primary, triple-negative breast cancer patients

mRNA profiles of circulating tumour cells (CTCs) were analysed in patients with triple‐negative breast cancer (TNBC) (pts) before (BT) and after therapy (AT) to identify additional treatment options. 2 × 5 mL blood of 51 TNBC pts and 24 non‐TNBC pts (HR+/HER2−; HR−/HER2+) was analysed for CTCs using the AdnaTest EMT‐2/Stem Cell Select™, followed by mRNA isolation and cDNA analysis for 17 genes by qPCR PIK3CA, AKT2, MTOR and the resistance marker AURKA and ERCC1 were predominantly expressed in all breast cancer subtypes, the latter ones especially AT. In TNBC pts, ERBB3, EGFR, SRC, NOTCH, ALK and AR were uniquely present and ERBB2+/ERBB3 + CTCs were found BT and AT in about 20% of cases. EGFR+/ERBB2+/ERBB3 + CTCs BT and ERBB2+/ERBB3 + CTCs AT significantly correlated with a shorter progression‐free survival (PFS; P = 0.01 and P = 0.02). Platinum‐based therapy resulted in a reduced PFS (P = 0.02) and an induction of PIK3CA expression in CTCs AT. In non‐TNBC pts, BT, the expression pattern in CTCs was similar. AURKA+/ERCC1 + CTCs were found in 40% of HR−/HER2 + pts BT and AT. In the latter group, NOTCH, PARP1 and SRC1 were only present AT and ERBB2 + CTCs completely disappeared AT. These findings might help to predict personalized therapy for TNBC pts in the future.

Optimization of the Enrichment of Circulating Tumor Cells for Downstream Phenotypic Analysis in Patients with Non-Small Cell Lung Cancer Treated with Anti-PD-1 Immunotherapy

The current study aimed at the optimization of circulating tumor cell (CTC) enrichment for downstream protein expression analyses in non-small cell lung cancer (NSCLC) to serve as a tool for the investigation of immune checkpoints in real time. Different enrichment approaches—ficoll density, erythrolysis, their combination with magnetic separation, ISET, and Parsortix—were compared in spiking experiments using the A549, H1975, and SKMES-1 NSCLC cell lines. The most efficient methods were tested in patients (n = 15) receiving immunotherapy targeting programmed cell death-1 (PD-1). Samples were immunofluorescently stained for a) cytokeratins (CK)/epithelial cell adhesion molecule (EpCAM)/leukocyte common antigen (CD45), and b) CK/programmed cell death ligand-1 (PD-L1)/ indoleamine-2,3-dioxygenase (IDO). Ficoll, ISET, and Parsortix presented the highest yields and compatibility with phenotypic analysis; however, at the patient level, they provided discordant CTC positivity (13%, 33%, and 60% of patients, respectively) and enriched for distinct CTC populations. IDO and PD-L1 were expressed in 44% and 33% and co-expressed in 19% of CTCs. CTC detection was associated with progressive disease (PD) (p = 0.006), reduced progression-free survival PFS (p = 0.007), and increased risk of relapse (hazard ratio; HR: 10.733; p = 0.026). IDO-positive CTCs were associated with shorter PFS (p = 0.039) and overall survival OS (p = 0.021) and increased risk of death (HR: 5.462; p = 0.039). The current study indicates that CTC analysis according to distinct immune checkpoints is feasible and may provide valuable biomarkers to monitor NSCLC patients treated with anti-PD-1 agents.

Overcoming trastuzumab resistance in HER2-positive breast cancer using combination therapy

Human epidermal growth factor receptor 2 (HER2)-positive breast cancer (BC) comprises around 20-30% of all BC subtypes and is correlated with poor prognosis. For many years, trastuzumab, a monoclonal antibody, has been used to inhibit the HER2 activity. Though, the main resistance to trastuzumab has challenged the use of this drug in the management of HER2-positive BC. Therefore, the determination of resistance mechanisms and the incorporation of new agents may lead to the development of a better blockade of the HER family receptor signaling. During the last few years, some therapeutic drugs have been developed for treating patients with trastuzumab-resistant HER2-positive BC that have more effective influences in the management of this condition. In this regard, the present study aimed at reviewing the mechanisms of trastuzumab resistance and the innovative therapies that have been investigated in trastuzumab-resistant HER2-positive BC subjects.

Clinical Relevance of Immune Checkpoints on Circulating Tumor Cells in Breast Cancer

The role of CD47 and PD-L1 expression on circulating tumor cells (CTCs) remains unclear, and it is currently unknown whether their distribution varies between the blood and tumor tissue in breast cancer (BC). In this study, CD47 and PD-L1 expression was investigated a) on peripheral blood mononuclear cell (PBMC) cytospins from early (n = 100) and metastatic (n = 98) BC patients, by triple immunofluorescence for CD47/PD-L1/Cytokeratins, and b) on matched primary and/or metastatic tumor tissue from CTC-positive patients using immunohistochemistry. CD47+and/orPD-L1+ CTCs were detected in 11%, 16.9%, and 29.6% of early, recurrent, and de novo metastatic patients (p = 0.016). In metastatic disease, CD47^highand/orPD-L1^high CTCs were associated with disease progression (p = 0.005) and shorter progression-free survival (PFS) (p = 0.010), and independently predicted for an increased risk of relapse (HR: 2.719; p = 0.008) and death (HR: 2.398; p = 0.034). PD-L1 expression rates differed between CTCs and tissue tumor cells and between peripheral blood mononuclear cells (PBMCs) and tumor-infiltrating lymphocytes (TILs) (positive concordance of 3.8% and 4%, respectively). CD47 expression also differed between CTCs and tumor cells (positive concordance of 11.5%). In conclusion, CTCs expressing CD47 and PD-L1 have independent poor prognostic implications in metastatic BC, indicating a potential role of innate and adaptive immune evasion mechanisms in their metastatic potential. The clinical value of the parallel assessment of the peripheral and local immune response merits further evaluation in BC.

The prognostic value of JUNB-positive CTCs in metastatic breast cancer: from bioinformatics to phenotypic characterization

Background

Circulating tumor cells (CTCs) are important for metastatic dissemination of cancer. They can provide useful information, regarding biological features and tumor heterogeneity; however, their detection and characterization are difficult due to their limited number in the bloodstream and their mesenchymal characteristics. Therefore, new biomarkers are needed to address these questions.

Methods

Bioinformatics functional enrichment analysis revealed a subgroup of 24 genes, potentially overexpressed in CTCs. Among these genes, the chemokine receptor CXCR4 plays a central role. After prioritization according to the CXCR4 corresponding pathways, five molecules (JUNB, YWHAB, TYROBP, NFYA, and PRDX1) were selected for further analysis in biological samples. The SKBR3, MDA-MB231, and MCF7 cell lines, as well as PBMCs from normal (n = 10) blood donors, were used as controls to define the expression pattern of all the examined molecules. Consequently, 100 previously untreated metastatic breast cancer (mBC) patients (n = 100) were analyzed using the following combinations of antibodies: CK (cytokeratin)/CXCR4/JUNB, CK/NFYA/ΥWHΑΒ (14-3-3), and CK/TYROBP/PRDX1. A threshold value for every molecule was considered the mean expression in normal PBMCs.

Results

Quantification of CXCR4 revealed overexpression of the receptor in SKBR3 and in CTCs, following the subsequent scale (SKBR3>CTCs>Hela>MCF7>MDA-MB231). JUNB was also overexpressed in CTCs (SKBR3>CTCs>MCF7>MDA-MB231>Hela). According to the defined threshold for each molecule, CXCR4-positive CTCs were identified in 90% of the patients with detectable tumor cells in their blood. In addition, 65%, 75%, 14.3%, and 12.5% of the patients harbored JUNB-, TYROBP-, NFYA-, and PRDX-positive CTCs, respectively. Conversely, none of the patients revealed YWHAB-positive CTCs. Interestingly, JUNB expression in CTCs was phenotypically and statistically enhanced compared to patients’ blood cells (p = 0.002) providing a possible new biomarker for CTCs. Furthermore, the detection of JUNB-positive CTCs in patients was associated with poorer PFS (p = 0.015) and OS (p = 0.002). Moreover, JUNB staining of 11 primary and 4 metastatic tumors from the same cohort of patients revealed a dramatic increase of JUNB expression in metastasis.

Conclusions

CXCR4, JUNB, and TYROBP were overexpressed in CTCs, but only the expression of JUNB was associated with poor prognosis, providing a new biomarker and a potential therapeutic target for the elimination of CTCs.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1166-4) contains supplementary material, which is available to authorized users.

Liquid biopsy in breast cancer: A comprehensive review

Breast cancer is the most common cancer among women worldwide. Due to its complexity in nature, effective breast cancer treatment can encounter many challenges. Traditional methods of cancer detection such as tissue biopsy are not comprehensive enough to capture the entire genomic landscape of breast tumors. However, with the introduction of novel techniques, the application of liquid biopsy has been enhanced, enabling the improvement of various aspects of breast cancer management including early diagnosis and screening, prediction of prognosis, early detection of relapse, serial sampling and efficient longitudinal monitoring of disease progress and response to treatment. Various components of tumor cells released into the blood circulation can be analyzed in liquid biopsy sampling, some of which include circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), cell-free RNA, tumor-educated platelets and exosomes. These components can be utilized for different purposes. As an example, ctDNA can be sequenced for genetic profiling of the tumors to enhance individualized treatment and longitudinal screening. CTC plasma count analysis or ctDNA detection after curative tumor resection surgery could facilitate early detection of minimal residual disease, aiding in the initiation of adjuvant therapy to prevent recurrence. Furthermore, CTC plasma count can be assessed to determine the stage and prognosis of breast cancer. In this review, we discuss the advantages and limitations of the various components of liquid biopsy used in breast cancer diagnosis and will expand on aspects that require further focus in future research.

Circulating Tumor Cells with Stemness and Epithelial-to-Mesenchymal Transition Features Are Chemoresistant and Predictive of Poor Outcome in Metastatic Breast Cancer

Circulating tumor cells (CTCs) bearing phenotypes related to cancer stem cells (CSCs) and epithelial-to-mesenchymal transition (EMT) have been identified in breast cancer; however, their clinical significance is not clear. In the current study, we investigated the prognostic relevance of single CSC⁺/partial-EMT⁺ CTCs in patients with metastatic breast cancer and the effect of first-line chemotherapy on their incidence. For this purpose, triple immunofluorescence against cytokeratin, ALDH1, and TWIST1 was performed in peripheral blood mononuclear cell (PBMC) cytospins from 130 patients before and after first-line chemotherapy. CSC⁺/partial-EMT⁺ CTCs were characterized as cells co-expressing cytokeratin, high levels of ALDH1, and nuclear TWIST1. CSC⁺/partial-EMT⁺ CTCs were evident in 27.7% of patients at baseline and were correlated to lung metastases (P = 0.010) and decreased progression-free survival [PFS; median 10.2 (8.9-11.6) vs. 13.5 (11.3-15.7) months; P = 0.024]. Their detection was an independent factor predicting for increased risk of relapse [multivariate analysis; HR (95% confidence interval (CI)): 1.785 (1.171-2.720); P = 0.007]. In HER-2-negative patients, CSC⁺/partial-EMT⁺ CTCs were additionally associated with reduced overall survival (OS) [median 39 (26.2-51.9) vs. 51 (15.7-86.4) months; P = 0.020] and increased risk of death [multivariate analysis; HR (95% CI): 2.228 (1.066-4.655); P = 0.033]. Chemotherapy resulted in a significant increase in the incidence of CSC⁺/partial-EMT⁺ CTCs (mean CTC% per patient: 59.4% post vs. 39.5% pre; P = 0.018), which was subsequently confirmed only in HER2-negative patients (P = 0.040) and in non-responders at the end of treatment (P = 0.020). In conclusion, CSC⁺/partial-EMT⁺ CTCs represent a chemoresistant subpopulation, which independently predicts for unfavorable outcome in metastatic breast cancer. Efficient targeting of these CTCs could potentially increase patient survival.

Evaluation of α-tubulin, detyrosinated α-tubulin, and vimentin in CTCs: identification of the interaction between CTCs and blood cells through cytoskeletal elements

Background

Circulating tumor cells (CTCs) are the major players in the metastatic process. A potential mechanism of cell migration and invasion is the formation of microtentacles in tumor cells. These structures are supported by α-tubulin (TUB), detyrosinated α-tubulin (GLU), and vimentin (VIM). In the current study, we evaluated the expression of those cytoskeletal proteins in CTCs.

Methods

Forty patients with breast cancer (BC) (16 early and 24 metastatic) were enrolled in the study. CTCs were isolated using the ISET platform and stained with the following combinations of antibodies: pancytokeratin (CK)/VIM/TUB and CK/VIM/GLU. Samples were analyzed with the ARIOL platform and confocal laser scanning microscopy.

Results

Fluorescence quantification revealed that the ratios CK/TUB, CK/VIM, and CK/GLU were statistically increased in MCF7 compared with more aggressive cell lines (SKBR3 and MDA-MB-231). In addition, all of these ratios were statistically increased in MCF7 cells compared with metastatic BC patients’ CTCs (p = 0.0001, p = 0.0001, and p = 0.003, respectively). Interestingly, intercellular connections among CTCs and between CTCs and blood cells through cytoskeleton bridges were revealed, whereas microtentacles were increased in patients with CTC clusters. These intercellular connections were supported by TUB, VIM, and GLU. Quantification of the examined molecules revealed that the median intensity of TUB, GLU, and VIM was significantly increased in patients with metastatic BC compared with those with early disease (TUB, 62.27 vs 11.5, p = 0.0001; GLU, 6.99 vs 5.29, p = 0.029; and VIM, 8.24 vs 5.38, p = 0.0001, respectively).

Conclusions

CTCs from patients with BC aggregate to each other and to blood cells through cytoskeletal protrusions, supported by VIM, TUB, and GLU. Quantification of these molecules could potentially identify CTCs related to more aggressive disease.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-0993-z) contains supplementary material, which is available to authorized users.

Phenotypic characterization of circulating tumor cells in triple negative breast cancer patients

Introduction

Patients with triple negative breast cancer (TNBC), are considered as a poor prognosis group for whom no targeted therapies are currently available. The aim of the present study was to phenotypically characterize their CTCs in order to explore potential therapeutic targets.

Methods

PBMC's cytospins were prepared from 45 early (before and after adjuvant chemotherapy), 10 metastatic TNBC and 21 hormone receptor (HR) -positive patients. The expression of Cytokeratins (CK), ER, PR, EGFR and HER2 on CTCs was assessed using immunofluoresence staining and ARIOL analysis.

Results

In early stage TNBC, ER, PR, HER2 and EGFR expressing-CTCs were detected in 24.4%, 24.4%, 20% and 40% of patients before the initiation of adjuvant chemotherapy, and in 17.8%, 13.3% 6.7% and 51.1% respectively after the completion of adjuvant treatment. Triple staining experiments revealed distinct subpopulations of CTC expressed HR, and ErbB family receptors. In patients with metastatic disease, the frequency of HER2+ CTCs was significantly increased compared to adjuvant setting (60% vs 20%, p=0.014). The presence of CK⁺PR⁻ CTCs, before adjuvant treatment was associated with reduced OS (p=0.032) and DFI (p=0.04). Furthermore, the frequency of ER-, PR- and HER2+ CTCs was higher in HR(+) than in TNBC tumors (57.1%, p=0.006; 52.4%, p=0.021 and 52.38%, p=0.009, respectively).

Conclusions

The CTCs in patients with early TNBC are phenotypically heterogeneous based on the expression of HR, EGFR and HER2 both before and after the completion of adjuvant chemotherapy whereas the presence of HER2⁺ CTCs prevails during disease evolution. These findings could be of clinical relevance in terms of CTC targeting.

Establishment of a multimarker qPCR panel for the molecular characterization of circulating tumor cells in blood samples of metastatic breast cancer patients during the course of palliative treatment

Background

Circulating tumor cells (CTC) are discussed to be an ideal surrogate marker for individualized treatment in metastatic breast cancer (MBC) since metastatic tissue is often difficult to obtain for repeated analysis. We established a nine gene qPCR panel to characterize the heterogeneous CTC population in MBC patients including epithelial CTC, their receptors (EPCAM, ERBB2, ERBB3, EGFR) CTC in Epithelial-Mesenchymal-Transition [(EMT); PIK3CA, AKT2), stem cell-like CTC (ALDH1) as well as resistant CTC (ERCC1, AURKA] to identify individual therapeutic targets.

Results

At TP0, at least one marker was detected in 84%, at TP1 in 74% and at TP2 in 79% of the patients, respectively. The expression of ERBB2, ERBB3 and ERCC1 alone or in combination with AURKA was significantly associated with therapy failure. ERBB2 + CTC were only detected in patients not receiving ERBB2 targeted therapies which correlated with no response. Furthermore, patients responding at TP2 had a significantly prolonged overall-survival than patients never responding (p = 0.0090).

Patients and Methods

2 × 5 ml blood of 62 MBC patients was collected at the time of disease progression (TP0) and at two clinical staging time points (TP1 and TP2) after 8–12 weeks of chemo-, hormone or antibody therapy for the detection of CTC (AdnaTest EMT-2/StemCell Select™, QIAGEN Hannover GmbH, Germany). After pre-amplification, multiplex qPCR was performed. Establishment was performed using various cancer cell lines. PTPRC (Protein tyrosine phosphatase receptor type C) and GAPDH served as controls.

Conclusions

Monitoring MBC patients using a multimarker qPCR panel for the characterization of CTC might help to treat patients accordingly in the future.

Evaluation of PD-L1/PD-1 on circulating tumor cells in patients with advanced non-small cell lung cancer

Background:

Circulating tumor cells (CTCs) could escape from the immune system through the programmed death-ligand 1 (PD-L1)/programmed cell death protein 1 (PD-1) axis leading to the development of metastasis. The current study investigated the expression of PD-1/PD-L1 on CTCs isolated from non-small cell lung cancer (NSCLC) patients treated with chemotherapy.

Patients and methods:

CTCs were isolated from 30 chemo-naïve stage IV NSCLC patients before and after front-line chemotherapy using the ISET filtration platform. CTCs were detected by Giemsa and immunofluorescence (IF) staining. Samples were analyzed with the ARIOL system.

Results:

Giemsa staining revealed that 28 (93.3%) out of 30 and 9 (81.8%) out of 11 patients had detectable CTCs at baseline and after the third chemotherapy cycle, respectively. Cytokeratin (CK)+/CD45- CTCs by IF could be detected in 17 of 30 (56.7%) patients at baseline and in 8 of 11 (72.7%) after the third chemotherapy cycle. Spearman analysis revealed a significant correlation (p = 0.001) between Giemsa-positive and IF-positive (CK+/CD45-) CTCs. At baseline, PD-1 and PD-L1 expression was observed in 53% and in 47% CK-positive patients, respectively. After the third treatment cycle the corresponding numbers were 13% and 63% respectively. Median progression-free survival (PFS) was significantly shorter in patients with >3 PD-1(+) CTCs at baseline compared with those with <3 PD-1(+) CTCs (p = 0.022) as well as in patients with >1 Giemsa-positive tumor cells (p = 0.025).

Conclusion:

PD-1(+) and PD-L1(+) CTCs could be detected before and after front-line chemotherapy in patients with metastatic NSCLC. The presence of high PD-1(+) CTC numbers before treatment is associated with a poor patient clinical outcome.

Detecting Blood-Based Biomarkers in Metastatic Breast Cancer: A Systematic Review of Their Current Status and Clinical Utility

Reviews on circulating biomarkers in breast cancer usually focus on one single biomarker or a selective group of biomarkers. An overview summarizing the discovery and evaluation of all blood-based biomarkers in metastatic breast cancer is lacking. This systematic review aims to identify the available evidence of known blood-based biomarkers in metastatic breast cancer, regarding their clinical utility and state-of-the-art position in the validation process. The initial search yielded 1078 original studies, of which 420 were assessed for eligibility. A total of 320 studies were included in the final synthesis. A Development, Evaluation and Application Chart (DEAC) of all biomarkers was developed. Most studies focus on identifying new biomarkers and search for relations between these biomarkers and traditional molecular characteristics. Biomarkers are usually investigated in only one study (68.8%). Only 9.8% of all biomarkers was investigated in more than five studies. Circulating tumor cells, gene expression within tumor cells and the concentration of secreted proteins are the most frequently investigated biomarkers in liquid biopsies. However, there is a lack of studies focusing on identifying the clinical utility of these biomarkers, by which the additional value still seems to be limited according to the investigated evidence.