Real-time HER2 status detected on circulating tumor cells predicts different outcomes of anti-HER2 therapy in histologically HER2-positive metastatic breast cancer patients

Modeling the management of patients with human epidermal growth factor receptor 2-positive breast cancer with liquid biopsy: the future of precision medicine

PURPOSE OF REVIEW

In the evolving landscape of human epidermal growth factor receptor 2 (HER2)-positive breast cancer (BC) management, liquid biopsy offers unprecedented opportunities for guiding clinical decisions. Here, we review the most recent findings on liquid biopsy applications in HER2-positive BC and its potential role in addressing challenges specific to this BC subtype.

RECENT FINDINGS

Recent studies have highlighted the significance of liquid biopsy analytes, primarily circulating tumor DNA (ctDNA) and circulating tumor cells (CTCs), in stratifying patients' prognosis, predicting treatment response, and monitoring tumor evolution in both early and advanced stages of BC. Liquid biopsy holds promise in studying minimal residual disease to detect and potentially treat disease recurrence before it manifests clinically. Additionally, liquid biopsy may have significant implication in the management of brain metastasis, a major challenge in HER2-positive BC, and could redefine parameters for determining HER2 positivity. Combining ctDNA and CTCs is crucial for a comprehensive understanding of HER2-positive tumors, as they provide complementary insights.

SUMMARY

Research efforts are needed to address analytical challenges, validate, and broaden the application of liquid biopsy in HER2-positive BC. This effort will ultimately facilitate its integration into clinical practice, optimizing the care of patients with HER2-positive tumors.

Harnessing molecular probes for imaging of human epidermal growth factor receptor (HER) family

The human epidermal growth factor receptor (HER) family plays a critical role in the development, migration, and invasion of various cancers. Currently, the FDA has approved numerous targeting therapies for the HER family consist of small molecule drugs, monoclonal antibodies and antibody-drug conjugates. To facilitate precision therapy using currently approved targeted agents, early detection and quantification of each HER receptor are essential for assessment, treatment, and prognostic purposes. This study provides a comprehensive review of the latest advancements in detection and quantification of HER receptors, including traditional biopsies, liquid biopsies, and non-invasive detection methods. Although traditional histological methods, such as immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH), have yielded valuable insights, advancements in real-time and non-invasive detection technologies necessitate improved methods for the dynamic evaluation of HER status. This article also reviews several emerging real-time techniques for detecting and quantifying HER status in circulating tumor cells (CTCs) extracted from blood samples, as well as in vivo assessments using positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging. This review emphasizes the importance of continuous innovation in the application of HER receptor imaging technologies, with the goal of enhancing treatment outcomes and prognoses for cancer patients.

Knowledge-map and research trends of circulating tumor cells in breast cancer: a scientometric analysis

Assessing circulating tumor cells (CTCs) in early-stage breast cancer patients can help identify relapse risk for timely interventions. Molecular analysis of CTCs can reveal vulnerabilities for personalized treatment options in metastatic breast cancer. This study aims to summarize CTCs in breast cancer research understanding and evaluate research trends. Extracted from the Web of Science Core Collection, publications on CTCs in breast cancer studies spanning from January 1, 2008, to December 21, 2023, were included. Co-authorships, references, and keywords were analyzed using Bibliometrix R packages and VOSviewer software. References and keywords burst detection were conducted with CiteSpace, and BICOMB was utilized to generate high-frequency keyword layouts. Biclustering analysis of the binary co-keyword matrix was performed using gCLUTO. 1747 articles focusing on CTCs in breast cancer were identified. The USA and the University of Texas MD Anderson Cancer Center demonstrated the highest productivity at the national and institutional levels, respectively. The journal "CANCERS" had the highest publication outputs on this subject. Pantel K emerged as the foremost author with the highest publication and co-citation counts. Analysis of co-keywords unveiled five prominent research areas concerning CTCs in breast cancer. The prognostic and predictive roles of CTCs in breast cancer have substantial implications for clinical practice. Nevertheless, precise assessment of CTCs, encompassing its quantities and attributes through advanced technologies, and its role in detecting minimal residual disease in breast cancer, continue to pose notable challenges. In conclusion, recent advancements and trends in CTCs research in breast cancer are examined through scientometric analysis in this study. The results provide valuable insights for the formulation of novel approaches in CTCs research, emphasizing the current research frontiers.

Trastuzumab and first-line taxane chemotherapy in metastatic breast cancer patients with a HER2-negative tumor and HER2-positive circulating tumor cells: a phase II trial

PURPOSE

HER2 overexpressing circulating tumor cells (CTCs) are observed in up to 25% of HER2-negative metastatic breast cancer patients. Since targeted anti-HER2 therapy has drastically improved clinical outcomes of patients with HER2-positive breast cancer, we hypothesized that patients with HER2 overexpressing CTCs might benefit from the addition of trastuzumab to chemotherapy.

METHODS

In this single-arm, phase II trial, patients with HER2-positive CTCs received trastuzumab as addition to first-line treatment with taxane chemotherapy. Patients with detectable CTCs but without HER2 overexpression that received taxane chemotherapy only, were used as control group. The primary outcome measure was progression-free rate at 6 months (PFR6), with a target of 80%. In November 2022, the study was terminated early due to slow patient accrual.

RESULTS

63 patients were screened, of which eight patients had HER2-positive CTCs and were treated with trastuzumab. The median number of CTCs was 15 per 7.5 ml of blood (range 1-131) in patients with HER2-positive CTCs, compared to median 5 (range 1-1047) in the control group. PFR6 was 50% in the trastuzumab group and 54% in the taxane monotherapy group, with no significant difference in median PFS (8 versus 9 months, p = 0.51).

CONCLUSION

No clinical benefit of trastuzumab was observed, although this study was performed in a limited number of patients. Additionally, we observed a strong correlation between the number of evaluable CTCs and the presence of HER2-positive CTCs. We argue that randomized studies investigating agents that are proven to be solely effective in the HER2-positive patient group in patients with HER2-positive CTCs and HER2-negative tissue are currently infeasible. Several factors contribute to this impracticality, including the need for more stringent thresholds, and the rapidly evolving landscape of cancer treatments.

Efficacy relevance of PD-L1 expression on circulating tumor cells in metastatic breast cancer patients treated with anti-PD-1 immunotherapy

PURPOSE

Breast cancer has become the leading cause of cancer mortality in women. Although immune checkpoint inhibitors targeting programmed death-1 (PD-1) are promising, it remains unclear whether PD-L1 expression on circulating tumor cells (CTCs) has predictive and prognostic values in predicting and stratifying metastatic breast cancer (MBC) patients who can benefit from anti-PD-1 immunotherapy.

METHODS

Twenty six MBC patients that received anti-PD-1 immunotherapy were enrolled in this study. The peptide-based Pep@MNPs method was used to isolate and enumerate CTCs from 2.0 ml of peripheral venous blood. The expression of PD-L1 on CTCs was evaluated by an established immunoscoring system categorizing into four classes (negative, low, medium, and high).

RESULTS

Our data showed that 92.3% (24/26) of patients had CTCs, 83.3% (20/26) of patients had PD-L1-positive CTCs, and 65.4% (17/26) of patients had PD-L1-high CTCs. We revealed that the clinical benefit rate (CBR) of patients with a cut-off value of ≥ 35% PD-L1-high CTCs (66.6%) was higher than the others (29.4%). We indicated that PD-L1 expression on CTCs from MBC patients treated with anti-PD-1 monotherapy was dynamic. We demonstrated that MBC patients with a cut-off value of ≥ 35% PD-L1-high CTCs had longer PFS (P = 0.033) and OS (P = 0.00058) compared with patients with a cut-off value of < 35% PD-L1-high CTCs.

CONCLUSION

Our findings suggested that PD-L1 expression on CTCs could predict the therapeutic response and clinical outcomes, providing a valuable predictive and prognostic biomarker for patients treated with anti-PD-1 immunotherapy.

Phenotypic Plasticity in Circulating Tumor Cells Is Associated with Poor Response to Therapy in Metastatic Breast Cancer Patients

Circulating tumor cells (CTCs) are indicators of metastatic spread and progression. In a longitudinal, single-center trial of patients with metastatic breast cancer starting a new line of treatment, a microcavity array was used to enrich CTCs from 184 patients at up to 9 timepoints at 3-month intervals. CTCs were analyzed in parallel samples from the same blood draw by imaging and by gene expression profiling to capture CTC phenotypic plasticity. Enumeration of CTCs by image analysis relying primarily on epithelial markers from samples obtained before therapy or at 3-month follow-up identified the patients at the highest risk of progression. CTC counts decreased with therapy, and progressors had higher CTC counts than non-progressors. CTC count was prognostic primarily at the start of therapy in univariate and multivariate analyses but had less prognostic utility at 6 months to 1 year later. In contrast, gene expression, including both epithelial and mesenchymal markers, identified high-risk patients after 6-9 months of treatment, and progressors had a shift towards mesenchymal CTC gene expression on therapy. Cross-sectional analysis showed higher CTC-related gene expression in progressors 6-15 months after baseline. Furthermore, patients with higher CTC counts and CTC gene expression experienced more progression events. Longitudinal time-dependent multivariate analysis indicated that CTC count, triple-negative status, and CTC expression of FGFR1 significantly correlated with inferior progression-free survival while CTC count and triple-negative status correlated with inferior overall survival. This highlights the utility of protein-agnostic CTC enrichment and multimodality analysis to capture the heterogeneity of CTCs.

HER2 status of CTCs by peptide-functionalized nanoparticles as the diagnostic biomarker of breast cancer and predicting the efficacy of anti-HER2 treatment

Efficacy of anti-human epidermal growth factor receptor 2 (HER2) treatment is impacted by tissue-based evaluation bias due to tumor heterogeneity and dynamic changes of HER2 in breast cancer. Circulating tumor cell (CTC)-based HER2 phenotyping provides integral and real-time assessment, benefiting accurate HER2 diagnosis. This study developed a semi-quantitative fluorescent evaluation system of HER2 immunostaining on CTCs by peptide-functionalized magnetic nanoparticles (Pep@MNPs) and immunocytochemistry (ICC). 52 newly-diagnosed advanced breast cancer patients were enrolled for blood samples before and/or after first-line treatment, including 24 patients who were diagnosed with HER2+ tumors and treated with anti-HER2 drugs. We enumerated CTCs and assessed levels of HER2 expression on CTCs in 2.0 ml whole blood. Enumerating CTCs at baseline could distinguish cancer patients (sensitivity, 69.2%; specificity, 100%). 80.8% (42/52) of patients had at least one CTCs before therapy. Patients with <3 CTCs at baseline had significantly longer progression-free survival (medians, 19.4 vs. 9.2 months; log-rank p = 0.046) and overall survival (medians, not yet reached; log-rank p = 0.049) than those with ≥3 CTCs. Both HER2+ and HER2-low patients could be detected with HER2 overexpression on CTCs (CTC-HER2+) (52.6%, 44.4%, respectively), whereas all the HER2-negative patients had no CTC-HER2+ phenotype. Among HER2+ patients with ≥3 CTCs at baseline, objective response only appeared in pretherapeutic CTC-HER2+ cohort (60.0%), rather than in CTC-HER2- cohort (0.0%) (p = 0.034). In conclusion, we demonstrate the significance of CTC enumeration in diagnosis and prognosis of first-line advanced breast cancer, and highlight the value of CTC-HER2 status in predicting efficacy of anti-HER2 treatment.

Heterogeneity of HER2 Expression in Circulating Tumor Cells of Patients with Breast Cancer Brain Metastases and Impact on Brain Disease Control

Simple Summary

Results from a previous study suggested that the number of circulating tumor cells (CTC) might have a role as a biomarker of early distant brain failure in patients with breast cancer brain metastases (BCBM). However, it remains largely underexplored whether heterogeneous HER2 expression in CTC may have a prognostic implication. We evaluated the status of HER2 expression in CTC before and after radiotherapy/radiosurgery for BCBM and observed that the presence of HER2 expression in any moment was associated with longer distant brain failure-free survival, irrespective of the primary immunophenotype of the breast tumor. This finding suggests that the status of HER2 expression in CTC has the potential to improve the treatment selection for patients with BCBM.

Abstract

HER2 expression switching in circulating tumor cells (CTC) in breast cancer is dynamic and may have prognostic and predictive clinical implications. In this study, we evaluated the association between the expression of HER2 in the CTC of patients with breast cancer brain metastases (BCBM) and brain disease control. An exploratory analysis of a prospective assessment of CTC before (CTC1) and after (CTC2) stereotactic radiotherapy/radiosurgery (SRT) for BCBM in 39 women was performed. Distant brain failure-free survival (DBFFS), the primary endpoint, and overall survival (OS) were estimated. After a median follow-up of 16.6 months, there were 15 patients with distant brain failure and 16 deaths. The median DBFFS and OS were 15.3 and 19.5 months, respectively. The median DBFFS was 10 months in patients without HER2 expressed in CTC and was not reached in patients with HER2 in CTC (p = 0.012). The median OS was 17 months in patients without HER2 in CTC and was not reached in patients with HER2 in CTC (p = 0.104). On the multivariate analysis, DBFFS was superior in patients who were primary immunophenotype (PIP) HER2-positive (HR 0.128, 95% CI 0.025–0.534; p = 0.013). The expression of HER2 in CTC was associated with a longer DBFFS, and the switching of HER2 expression between the PIP and CTC may have an impact on prognosis and treatment selection for BCBM.

A Phase 1 Proof of Concept Study Evaluating the Addition of an LSD1 Inhibitor to Nab-Paclitaxel in Advanced or Metastatic Breast Cancer (EPI-PRIMED)

Objective

Lysine-Specific Demethylase-1 (LSD1) is overexpressed in breast cancer cells and facilitate mesenchymal properties which may contribute to therapeutic resistance and cancer progression. The purpose of this study was to investigate the safety of combination, nab-paclitaxel and phenelzine, an irreversible LSD1 inhibitor in patients with metastatic breast cancer (mBC).

Methods

Eligible patients with mBC were treated with nab-paclitaxel (100mg/m²) weekly for 3 weeks with one week break in a 28-day cycle. Dose escalation of phenelzine followed the Cumulative Cohort Design and phenelzine treatment commenced from day 2 of first cycle. Eleven patients were screened, and eligible patients were enrolled in cohorts with the dose of phenelzine ranging from 45mg to 90mg.

Results

The Optimum Biological Dose was established at 60mg of phenelzine daily in combination with nab-paclitaxel and considered as the recommended phase 2 dose. Most (95%) of adverse events were grade 1 or 2 with two grade 3 events being diarrhea and neutropenia at 45mg and 60mg phenelzine respectively, with no unexpected toxicity/deaths. Commonly reported toxicities were fatigue (n=4,50%), dizziness (n=6,75%), neutropenia (n=3,37.5%), peripheral neuropathy (n=3,37.5%), diarrhea (n=2,25%), and hallucination (n=2,25%). After a median follow up of 113 weeks, all patients showed disease progression on trial with 4 patients being alive at the time of data cut off, including one patient with triple negative breast cancer. Median progression-free survival was 34 weeks. Significant inhibition of LSD1 and suppression of mesenchymal markers in circulating tumor cells were noted.

Conclusion

Phenelzine in combination with nab-paclitaxel was well tolerated, without any unexpected toxicities in patients with mBC and demonstrated evidence of antitumor activity. For the first time, this proof-of-concept study showed in-vivo inhibition of LSD1 suppressed mesenchymal markers, which are known to facilitate generation of cancer stem cells with metastatic potential. Clinical Trial Registration: ClinicalTrials.Gov NCT03505528, UTN of U1111-1197-5518.

Relevance of Circulating Tumor Cells as Predictive Markers for Cancer Incidence and Relapse

Shedding of cancer cells from the primary site or undetectable bone marrow region into the circulatory system, resulting in clinically overt metastasis or dissemination, is the hallmark of unfavorable invasive cancers. The shed cells remain in circulation until they extravasate to form a secondary metastatic lesion or undergo anoikis. The circulating tumor cells (CTCs) found as single cells or clusters carry a plethora of information, are acknowledged as potential biomarkers for predicting cancer prognosis and cancer progression, and are supposed to play key roles in determining tailored therapies for advanced diseases. With the advent of novel technologies that allow the precise isolation of CTCs, more and more clinical trials are focusing on the prognostic and predictive potential of CTCs. In this review, we summarize the role of CTCs as a predictive marker for cancer incidence, relapse, and response to therapy.

Evaluation of Liquid Biopsy in Patients with HER2-Positive Breast Cancer

Breast cancer is one of the common malignant tumors, and liquid biopsy has become a hot spot for clinical testing. To clarify the detection effect of liquid biopsy in breast cancer, we collected peripheral blood of HER2-positive (human epidermal growth factor receptor 2-positive) patients. Circulating tumor cells (CTCs) were isolated and analyzed. HER2 expression on CTCs was detected. The results showed that in the 198 HER2-positive samples, the CTC detection rate was 79.8% (158/198), and the mean number of CTCs was 21, ranging from 1 to 63/7.5 mL peripheral blood. Only 41.1% (65/158) of patients had histology and CTC HER2 status consistent with the remaining 58.9% (93/158) of patients, although their histological HER2 was positive, and CTC HER2 was negative. Our study confirmed the value of CTC HER2 real-time status testing in HER2-positive breast cancer patients. The inconsistency in HER2 status between CTCs and histology may be related to the time interval between CTCs and histological HER2 detection, suggesting that real-time HER2 detection is necessary for histological HER2-positive patients.

Clinical significance of circulating tumor cells in the response to trastuzumab for HER2-negative metastatic gastric cancer

PURPOSE

The prognosis of metastatic gastric cancer has improved due to trastuzumab in patients with HER2 positive. Circulating tumor cells (CTCs) have been examined as a prognostic predictor in gastric cancer. The clinical advantage of trastuzumab was examined in gastric cancer patients with HER2-negative tumor tissues and HER2-positive CTCs.

METHODS

A total of 105 patients with metastatic or recurrence gastric cancer were enrolled. All patients were examined HER2 expression in CTC using the CellSearch system in blood specimens.

RESULTS

CTCs were detected in 65 of 105 patients (61.9%) and 61 patients were divided into three groups: Group A (n = 27), histological HER2-positive; Group B (n = 17), histological HER2-negative and HER2-positive CTCs; and Group C (n = 17), HER2-negative on histology and CTCs. Patients received capecitabine plus cisplatin. Groups A and B were additionally treated by trastuzumab. There was no relationship between tumor tissues and CTCs in HER2 expression. Even if group B had no histological HER2 expression, group B showed a good prognosis as same as group A, and group C had a significantly worse overall survival than groups A and B. The multivariate analysis demonstrated that HER2-expression on CTCs was an independent prognostic factor for both overall and progression-free survival.

CONCLUSION

The present results indicate the potential clinical utility of trastuzumab combined chemotherapy in patients with HER2-positive CTCs even if they are histologically HER2-negative.

Influence of adjuvant radiotherapy on circulating epithelial tumor cells and circulating cancer stem cells in primary non-metastatic breast cancer

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CETCs have the same molecular properties as the cells in the primary tumor.

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Circulating cancer stem cells can be successfully identified in the blood of breast cancer patients and monitored during RT.

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Patients after neoadjuvant chemotherapy had the highest number of CETCs prior to RT but the CETC counts decreased significantly during RT indicating that this group of patients could most likely benefit from adjuvant RT.

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Increase in cCSC numbers during RT could be a predictor for early recurrence of cancer disease.

Background

: There is an unmet need to identify biomarkers that directly reflect response to adjuvant radiotherapy (RT). Circulating epithelial tumor cells (CETCs) represent the liquid component of solid tumors and are responsible for metastatic relapse. CETC subsets with cancer stem cell characteristics, circulating cancer stem cells (cCSCs), play a pivotal role in the metastatic cascade. Monitoring the most aggressive subpopulation of CETCs could reflect the aggressiveness of the remaining tumor burden. There is limited data on the detection and monitoring changes in CETC and cCSC numbers during RT in early breast cancer.

Methods

: CETC numbers were analyzed prior to, at midterm and at the end of RT in 52 primary non-metastatic breast cancer patients. Hormone receptor status was determined in CETCs prior to and at the end of RT. For the identification of cCSCs cell suspensions from the peripheral blood of patients were cultured in vitro under conditions favoring growth of tumorspheres.

Results

: Hormone receptor status in CETCs before RT was comparable to that in primary tumor tissue. Prior to RT numbers of CETCs correlated with aggressiveness of primary tumors. cCSCs could be successfully identified and monitored during RT. Prior to RT patients treated with neoadjuvant chemotherapy had significantly higher numbers of CETCs and tumorspheres compared to patients after adjuvant chemotherapy. During RT, the number of CETCs decreased continuously in patients after neoadjuvant chemotherapy but not after adjuvant chemotherapy.

Conclusion

: Monitoring the number of CETCs and the CETC subset with cancer stem cell properties during RT may provide additional clinically useful prognostic information.

Mesenchymal Characteristics and Predictive Biomarkers on Circulating Tumor Cells for Therapeutic Strategy

Metastasis-related events are the primary cause of cancer-related deaths, and circulating tumor cells (CTCs) have a pivotal role in metastatic relapse. CTCs include a variety of subtypes with different functional characteristics. Interestingly, the epithelial-mesenchymal transition (EMT) markers expressed in CTCs are strongly associated with poor clinical outcome and related to the acquisition of circulating tumor stem cell (CTSC) features. Recent studies have revealed the existence of CTC clusters, also called circulating tumor microemboli (CTM), which have a high metastatic potential. In this review, we present current opinions regarding the clinical significance of CTCs and CTM with a mesenchymal phenotype as clinical surrogate markers, and we summarize the therapeutic strategy according to phenotype characterization of CTCs in various types of cancers for future precision medicine.

NK cells-directed therapies target circulating tumor cells and metastasis

Metastasis is the major cause of cancer-related deaths. Invasive primary cancers often metastasize after circulating tumor cells (CTCs) enter the bloodstream or lymph node to colonize adjacent tissue or distant anatomical locations. CTCs interact with immune cells and metastatic microenvironments, survival signaling, and chemotherapeutic resistance. Among immune cells, natural killer (NK) cells can, directly and indirectly, interact with CTCs to control cancer metastasis. Understanding the molecular mechanisms that drive NK cells mediated recognition and elimination of CTCs may pave the way for a new generation of anti-CTC molecularly targeted immunotherapies. In this review, we will discuss i) the role of CTCs in metastases, ii) CTCs in the context of the tumor microenvironment, iii) CTCs immune escape, and finally, iv) the potentials of NK cell-based therapies alone, or in combination with nanomedicine for targeted-immunotherapies of metastatic diseases.

Prognostic value of HER2 status on circulating tumor cells in advanced-stage breast cancer patients with HER2-negative tumors

PURPOSE

Discordance between HER2 expression in tumor tissue (tHER2) and HER2 status on circulating tumor cells (cHER2) has been reported. It remains largely underexplored whether patients with tHER2^-/cHER2⁺ can benefit from anti-HER2 targeted therapies.

METHODS

cHER2 status was determined in 105 advanced-stage patients with tHER2^- breast tumors. Association between cHER2 status and progression-free survival (PFS) was analyzed by univariate and multivariate Cox models and survival differences were compared by Kaplan-Meier method.

RESULTS

Compared to the patients with low-risk cHER2 (cHER2⁺  < 2), those with high-risk cHER2 (cHER2⁺  ≥ 2) had shorter survival time and an increased risk for disease progression (hazard ratio [HR] 2.16, 95% confidence interval [CI] 1.20-3.88, P = 0.010). Among the patients with high-risk cHER2, those who received anti-HER2 targeted therapies had improved PFS compared with those who did not (HR 0.30, 95% CI 0.10-0.92, P = 0.035). In comparison, anti-HER2 targeted therapy did not affect PFS among those with low-risk cHER2 (HR 0.70, 95% CI 0.36-1.38, P = 0.306). Similar results were obtained after adjusting covariates. A longitudinal analysis of 67 patients with cHER2 detected during follow-ups found that those whose cHER2 status changed from high-risk at baseline to low-risk at first follow-up exhibited a significantly improved survival compared to those whose cHER2 remained high-risk (median PFS: 11.7 weeks vs. 2.0 weeks, log-rank P = 0.001).

CONCLUSION

In advanced-stage breast cancer patients with tHER2^- tumors, cHER2 status has the potential to guide the use of anti-HER2 targeted therapy in patients with high-risk cHER2.

Longitudinal HER2 amplification tracked in circulating tumor DNA for therapeutic effect monitoring and prognostic evaluation in patients with breast cancer

Background

Human epidermal growth factor receptor 2(HER2) status is a crucial predictive factor for prognostic assessment and targeted therapy selection, which may be influenced by intratumor heterogeneity and molecular divergence between the primary site and different metastases. Therefore, we performed a prospective study to confirm the concordance of HER2 amplification in circulating tumor DNA(ctDNA) with primary tumor tissue and verified its clinical implications.

Methods

A total of 105 breast cancer patients were enrolled, and dynamic monitoring of HER2 copy numbers in ctDNA was conducted in 31 participants during the treatment. Totally 186 plasma samples were prospectively obtained and blinded to test HER2 copy numbers in ctDNA based on low-coverage whole genome sequencing(WGS) by next-generation sequencing(NGS).

Results

Comparing HER2 copy numbers in ctDNA collected before the initiation of next line of anticancer treatment with primary tumor tissue, the concordant rate of HER2 amplification was 86.5%(χ² = 52.901, p < 0.001), with a positive and negative predictive value of 94.9% and 80.7%, respectively. Histopathologically positive, high-level amplification of HER2 copy numbers in the baseline was significantly correlated with best objective response during the anticancer therapy(p = 0.010). Moreover, HER2 copy numbers fluctuated with HER2-targeted therapeutic response, and the patients with a constantly positive level after 6 weeks of treatment appeared to suffer from significantly reduced progression free survival(p < 0.001).

Conclusions

HER2 amplification in ctDNA, with a concordance rate of over 80% with primary tumors, may be a predictive index for prognostic evaluation and therapeutic response monitoring in a noninvasive, repeatable and practical method for breast cancer patients.

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The concordance between HER2 amplification in ctDNA and tumor tissues was 86.5%.

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The positive and negative predictive value surpassed previous studies.

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HER2 copy numbers in ctDNA may predict the prognosis of anti-HER2 therapy.

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HER2 copy numbers in ctDNA may predict response in HER2 positive breast cancer.

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The study of various-stage patients may be closer to real-world clinical practice.

Liquid biopsies

Liquid biopsy is based on minimally invasive blood tests and has a high potential to significantly change the therapeutic strategy in cancer patients, providing an extremely powerful and reliable noninvasive clinical tool for the individual molecular profiling of patients in real time. Liquid biopsy approaches include the analysis of circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), circulating miRNAs, and tumor-derived extracellular vesicles (EVs) that are shed from primary tumors and their metastatic sites into peripheral blood. The major advantage of liquid biopsy analysis is that it is minimally invasive, and can be serially repeated, thus allowing extracting information from the tumor in real time. Moreover, the identification of predictive biomarkers in peripheral blood that can monitor response to therapy in real time holds a very strong potential for novel approaches in the therapeutic management of cancer patients. In this review, we summarize recent knowledge on CTCs and ctDNA and discuss future trends in the field.

Detecting and phenotyping of aneuploid circulating tumor cells in patients with various malignancies

Circulating tumor cells (CTCs) have been exclusively studied and served to assess the clinical outcomes of treatments and progression of cancer. Most CTC data have mainly been derived from distinct cohorts or selected tumor types. In the present study, a total of 594 blood samples from 479 cases with 19 different carcinomas and 30 healthy samples were collected and analyzed by Subtraction enrichment method combined with immunostaining-fluorescence in situ hybridization (iFISH). Non-hematopoietic cells with aneuploid chromosome 8 (more than 2 copies) were regarded as positive CTCs. The results showed that none of CTCs was found in all 30 healthy samples. The overall positive rate of CTCs was 89.0% in diagnosed cancer patients (ranging from 75.0% to 100.0%). Average number of 11, 5, 8 and 4 CTCs per 7.5 mL was observed in lung cancer, liver cancer, renal cancer and colorectal cancer, respectively. Among 19 different carcinomas, the total number of CTCs, tetraploid chromosome 8, polyploid chromosome 8, CTM (Circulating tumor microemboli) and large CTCs in patients with stage Ⅲ and Ⅳ were statistically higher than patients with stage Ⅰ and Ⅱ (P < 0.05). Furthermore, EpCAM expression was more frequently found in most CTCs than vimentin expression, confirming that these CTCs were of epithelial origin. In addition, small and large CTCs were also classified, and the expression of vimentin was mostly observed in small CTCs and CTM. Our results revealed that there are higher numbers of CTCs, tetraploid, polyploid and large CTCs in patients with stage Ⅲ and Ⅳ, indicating that the quantification of chromosome ploidy performed by SE-iFISH for CTCs might be a useful tool to predict and evaluate therapeutic efficacy as well as to monitoring disease progression.

Detection of HER2-positive Circulating Tumor Cells Using the LiquidBiopsy System in Breast Cancer

BACKGROUND

Most previous studies of circulating tumor cells (CTCs) are based on the CellSearch platform, but CellSearch has a number of limitations. This study aimed to use the LiquidBiopsy system and immunofluorescence to test the human epidermal growth factor receptor 2 (HER2) status of CTCs in patients with breast cancer.

MATERIALS AND METHODS

The LiquidBiopsy system was used to detect HER2-positive (HER2⁺) cells in whole blood by microfluidic immunomagnetic bead screening and immunofluorescence assay, according to the manufacturer;s instructions. HER2 expression on CTCs was assessed using the Ariol system, calibrated through spiking experiments of 100 cells (BT474, SKBR3, A431, and MDA-MB-231) and 2.5 × 10⁷ white blood cells/mL from healthy donors. Seventy-one patients with breast cancer and 107 non-cancer donors consented to provide blood.

RESULTS

Based on breast cancer cell lines experiments, HER2⁺ CTCs were defined as CTCs with HER2 immunofluorescence intensity ≥ 3.5 times higher than the CD45 immunofluorescence intensity (100% sensitivity and 99.9% specificity). Among the 71 patients with breast cancer, 31 (43.7%) had HER2⁺ tumor. Among the HER2⁺ patients, 41.9% (13/31) were found to be HER2⁺ based on CTC ≥ 1, and 25.8% (8/31) were positive based on CTC ≥ 3. In HER2-negative patients by pathologic examination, 1 (2.5%) patient was found to have ≥ 3 HER2⁺ CTCs, whereas 15 (37.5%) patients had ≥ 1 HER2⁺ CTC. HER2⁺ CTCs were detected at all stages, even in early breast cancer, but the detection rate was higher in metastatic breast cancer.

CONCLUSION

This proof-of-concept study strongly suggests that HER2⁺ CTCs can be detected using the LiquidBiopsy system.

The Interplay between Circulating Tumor Cells and the Immune System: From Immune Escape to Cancer Immunotherapy

Circulating tumor cells (CTCs) have aroused increasing interest not only in mechanistic studies of metastasis, but also for translational applications, such as patient monitoring, treatment choice, and treatment change due to tumor resistance. In this review, we will assess the state of the art about the study of the interactions between CTCs and the immune system. We intend to analyze the impact that the cells of the immune system have in limiting or promoting the metastatic capability of CTCs. To this purpose, we will examine studies that correlate CTCs, immune cells, and patient prognosis, and we will also discuss relevant animal models that have contributed to the understanding of the mechanisms of immune-mediated metastasis. We will then consider some studies in which CTCs seem to play a promising role in monitoring cancer patients during immunotherapy regimens. We believe that, from an accurate and profound knowledge of the interactions between CTCs and the immune system, new immunotherapeutic strategies against cancer might emerge in the future.

Detection of HER2 Amplification in Circulating Tumor Cells of HER2-Negative Gastric Cancer Patients

A key to the successful use of targeted cancer therapy is the ability to preselect patients who are likely to benefit from the treatment according to molecular markers. Assessment for predicting therapy response is mostly done using tumor biopsies. However, these might not truly represent all of the patient's malignant cells because of tumor heterogeneity and/or clonal evolution during disease progression. One potential strategy that can complement primary tumor biopsy is the analysis of circulating tumor cells (CTCs). In this study, we analyzed CTCs of patients with gastric cancer (GC) to find those who were likely to benefit from trastuzumab therapies. We developed an imaging-based method that enabled CTC identification simultaneously with evaluation of HER2 gene amplification (the 3D-IF-FISH method). Then we performed a study enrolling 101 GC patients in whom we analyzed CTCs by both 3D-IF-FISH and an FDA-approved CellSearch system. As compared with the CellSearch system, 3D-IF-FISH methods identified a higher number of patients whose primary tumors were HER2- but who had HER2+ CTCs, suggesting that the 3D-IF-FISH method is effective in preselecting patients for trastuzumab therapies. To demonstrate this, we performed an exploratory clinical study to evaluate the clinical benefits of trastuzumab treatment for advanced GC patients (n = 15) whose primary tumors were HER2-, but whose CTCs showed HER2 amplification. An interim evaluation after the first stage showed that these preselected patients had response rates comparable to those reported in the trastuzumab-plus-chemotherapy arm of the ToGA study. The present study offers a new, non-invasive strategy to select patients who are likely to benefit from trastuzumab-based therapies, despite their primary biopsy being HER2-negative. (UMIN ID: UMIN000008622).

Clinical applications of the CellSearch platform in cancer patients

The CellSearch® system (CS) enables standardized enrichment and enumeration of circulating tumor cells (CTCs) that are repeatedly assessable via non-invasive "liquid biopsy". While the association of CTCs with poor clinical outcome for cancer patients has clearly been demonstrated in numerous clinical studies, utilizing CTCs for the identification of therapeutic targets, stratification of patients for targeted therapies and uncovering mechanisms of resistance is still under investigation. Here, we comprehensively review the current benefits and drawbacks of clinical CTC analyses for patients with metastatic and non-metastatic tumors. Furthermore, the review focuses on approaches beyond CTC enumeration that aim to uncover therapeutically relevant antigens, genomic aberrations, transcriptional profiles and epigenetic alterations of CTCs at a single cell level. This characterization of CTCs may shed light on the heterogeneity and genomic landscapes of malignant tumors, an understanding of which is highly important for the development of new therapeutic strategies.

Nanotechnology-Based Strategies for Early Cancer Diagnosis Using Circulating Tumor Cells as a Liquid Biopsy

Circulating tumor cells (CTCs) are cancer cells that shed from a primary tumor and circulate in the bloodstream. As a form of “tumor liquid biopsy”, CTCs provide important information for the mechanistic investigation of cancer metastasis and the measurement of tumor genotype evolution during treatment and disease progression. However, the extremely low abundance of CTCs in the peripheral blood and the heterogeneity of CTCs make their isolation and characterization major technological challenges. Recently, nanotechnologies have been developed for sensitive CTC detection; such technologies will enable better cell and molecular characterization and open up a wide range of clinical applications, including early disease detection and evaluation of treatment response and disease progression. In this review, we summarize the nanotechnology-based strategies for CTC isolation, including representative nanomaterials (such as magnetic nanoparticles, gold nanoparticles, silicon nanopillars, nanowires, nanopillars, carbon nanotubes, dendrimers, quantum dots, and graphene oxide) and microfluidic chip technologies that incorporate nanoroughened surfaces and discuss their key challenges and perspectives in CTC downstream analyses, such as protein expression and genetic mutations that may reflect tumor aggressiveness and patient outcome.

Discordance in Human Epidermal Growth Factor Receptor 2 (HER2) Phenotype Between Primary Tumor and Circulating Tumor Cells in Women With HER2-Negative Metastatic Breast Cancer

Purpose

Discordance in human epidermal growth factor receptor 2 (HER2) status between primary tumor and metastases might have important implications for treatment response and therapy decisions. Here, we evaluate both the frequency of circulating tumor cells (CTCs) and the factors predicting HER2 discordance between primary tumor and CTCs as a potential surrogate for tumor biology and tumor heterogeneity in patients with metastatic breast cancer.

Patients and Methods

The number of CTCs in 7.5 mL of peripheral blood and HER2 status were evaluated in 1,123 women with HER2-negative metastatic breast cancer. HER2 discordance was defined as the presence of at least one CTC with a strong immunocytochemical HER2 staining intensity. Factors predicting discordance in HER2 phenotype were assessed using multivariable logistic regression.

Results

Overall, 711 (63.3%) of 1,123 screened patients were positive for CTCs (≥ one CTC). Discordance in HER2 phenotype between primary tumor and CTCs was observed in 134 patients (18.8%) and was significantly associated with histologic type (lobular v ductal; odds ratio [OR], 2.67; 95% CI, 1.63 to 4.39; P < .001), hormone receptor status (positive v negative; OR, 2.84; 95% CI, 1.15 to 7.02; P = .024), and CTC number (≥ five v one to four; OR, 7.64; 95% CI, 3.97 to 14.72; P < .001).

Conclusion

HER2 discordance between primary tumor and CTCs was observed in 18.8% of patients and was associated with histologic type, hormone receptor status of the primary tumor, and CTC number. The clinical utility of CTCs as liquid biopsy to assess tumor heterogeneity of metastatic disease and guide treatment decisions must be evaluated in prospective randomized trials.

Seed-specific expression and analysis of recombinant anti-HER2 single-chain variable fragment (scFv-Fc) in Arabidopsis thaliana

Antibodies to human epidermal growth factor receptor 2 (HER2) are a key element of breast cancer therapy; however, they are expensive to produce and their availability is limited. A seed-specific expression system can be used to produce recombinant proteins. We report a seed-specific expression system for the manufacture of anti-HER2 ScFv-Fc in Arabidopsis thaliana, driven by the Phaseolus vulgaris β-phaseolin promoter. Recombinant anti-HER2 ScFv-Fc was successfully and specifically expressed in seeds, and identified by protein analysis. The highest protein accumulation level, with a maximum of 1.1% of total soluble protein, was observed in mature seeds. We also demonstrated the anti-tumor potency of the plant-derived antibody against SK-BR-3 cells. These results suggest that seed-expression systems could contribute to the manufacture of commercial antibodies such as anti-HER2 ScFv-Fc.