MIMESIS: minimal DNA-methylation signatures to quantify and classify tumor signals in tissue and cell-free DNA samples.

DNA-methylation alterations are common in cancer and display unique characteristics that make them ideal markers for tumor quantification and classification. Here we present MIMESIS, a computational framework exploiting minimal DNA-methylation signatures composed by a few dozen informative DNA-methylation sites to quantify and classify tumor signals in tissue and cell-free DNA samples. Extensive analyses of multiple independent and heterogenous datasets including >7200 samples demonstrate the capability of MIMESIS to provide precise estimations of tumor content and to enable accurate classification of tumor type and molecular subtype. To assess our framework for clinical applications, we designed a MIMESIS-informed assay incorporating the minimal signatures for breast cancer. Using both artificial samples and clinical serial cell-free DNA samples from patients with metastatic breast cancer, we show that our approach provides accurate estimations of tumor content, sensitive detection of tumor signal and the ability to capture clinically relevant molecular subtype in patients' circulation. This study provides evidence that our extremely parsimonious approach can be used to develop cost-effective and highly scalable DNA-methylation assays that could support and facilitate the implementation of precision oncology in clinical practice.

Optimizing CDK4/6 inhibitors in advanced HR+/HER2- breast cancer: A personalized approach.

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) are now a backbone of treatment for hormone receptor-positive/human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer. CDK4/6i plus ET is more effective than ET alone in this setting; however, the risk of grade 3-4 adverse events also increases. Approved agents in this class have similar efficacies, but important differences due to their structural and pharmacological properties. We review biomarkers and discuss determinants to inform a rational approach to therapy choice when selecting the most appropriate ET and CDK4/6i partners. We also identify subgroups that may benefit from specific ET-CDK4/6i combinations and discuss strategies to overcome resistance. This personalized approach aims to minimize treatment-related toxicities that may affect patient QoL and compliance, and ultimately therapy efficacy.

A Dose-finding Study of Metronomic Oral Vinorelbine in Combination With Oral Cyclophosphamide and Bevacizumab in Patients With Advanced Breast Cancer.

BACKGROUND: Metronomic chemotherapy can induce disease control in patients with metastatic breast cancer (MBC) and has better safety profiles than conventional chemotherapy. Evidence suggests that cytotoxics can be anti-angiogenic in pre-clinical models and may have synergistic effects when combined with anti-vascular endothelial growth factor therapies. PATIENTS AND METHODS: Patients pretreated with ≥ 1 prior line of therapy for MBC received oral cyclophosphamide 50 mg daily in combination with oral vinorelbine at escalating doses of 20 mg (V20), 30 mg (V30), and 40 mg (V40) 3 times per week, and intravenous bevacizumab 15 mg/kg every 3 weeks. Patients with human epidermal growth factor receptor 2-positive disease were given the same regimen plus standard trastuzumab. Doses were escalated when 3 patients completed 3 treatment cycles of V20 and V30, without experiencing dose-limiting toxicities. The recommended dose was then tested in a further 6 patients. Circulating tumour cells and circulating endothelial cells (CEC) were measured in 30 mL of whole blood samples at baseline, after cycle 1, and at the disease progression. RESULTS: Fifteen patients were recruited from June 2013 to October 2015. The median age was 61 years (range, 29-72 years); 80% had estrogen receptor-positive and 33% had human epidermal growth factor receptor 2-positive disease. At least 67% had visceral metastases, and 80% had received ≥ 2 lines of prior treatment. No dose-limiting toxicities were observed at the 3 dose-levels, making V40 the recommended dose. Overall 8 (53%) patients developed grade 2 adverse events (arthralgia, n = 3 [20%]; asthenia, n = 2 [13%]; diarrhea, n = 2 [13%]; leukopenia, n = 2 [13%]). Bevacizumab was associated with grade 3 hypertension (n = 3 [20%]). Stable disease as best response was observed in 11 (73.3%) patients. The clinical benefit rate was 66.6% (10/15 patients). The median time to progression was 6.9 months. At baseline, CECs were more commonly detectable than circulating tumor cells; however, no statistical correlation was found between CEC kinetics and response. CONCLUSION: A metronomic vinorelbine dose of 40 mg combined with cyclophosphamide and bevacizumab is a promising treatment regimen in pretreated patients with MBC.

Early triple negative breast cancer: Are we getting better outcomes? A retrospective analysis from a single institution.

Overall survival (OS), disease-free survival (DFS), and distant recurrence-free interval (DRFI) were evaluated from 169 patients diagnosed with early triple negative breast cancer. Overall, 5 and 10 years OS, DFS, and DRFI were 77% and 65%; 60% and 46%; and 74% and 73%, respectively. Forty-seven patients did not receive chemotherapy. A separate analysis was performed excluding those patients. In this subgroup, 5- and 10-year OS, DFS, and DRFI were 86% and 77%; 68% and 54%, 77% both at 5 and 10 years. Prognosis is better than previously described; adjuvant chemotherapy should be offered to fit elderly patients if clinically warranted.

Prognostic role of serum thymidine kinase 1 activity in patients with hormone receptor-positive metastatic breast cancer: Analysis of the randomised phase III Evaluation of Faslodex versus Exemestane Clinical Trial (EFECT).

BACKGROUND: Thymidine kinase 1 (TK1) plays a critical role in DNA synthesis and cell proliferation. Recent studies have shown potential for serum TK1 activity (sTKa) as a prognostic marker and indicator of early response to endocrine therapy in advanced breast cancer. The aim of this study is to assess the correlation between sTKa and patient outcome. PATIENTS AND METHODS: The Evaluation of Faslodex versus Exemestane Clinical Trial (EFECT) was a double-blind, double-dummy, randomised trial of fulvestrant versus exemestane after progression on non-steroidal aromatase inhibitor therapy, in postmenopausal women with advanced breast cancer. Retrospective analyses of serum archived from EFECT were conducted. sTKa was assessed using the DiviTum® assay on samples collected at baseline, after three and six months of endocrine therapy, and at disease progression. RESULTS: The median time to progression (mTTP) for patients with low baseline sTKa levels was 5.03 months (95% confidence interval [CI]: 3.91-5.89) versus 2.57 months (95% CI: 2.04-3.52) in patients with high sTKa baseline levels (P < 0.0001). On treatment, patients whose sTKa increased from baseline had a significantly shorter mTTP (3.39 months, 95% CI: 2.14-4.11) than those without an sTKa increase (5.39 months, 95% CI: 4.01-6.68) (P = 0.0045). Similar results were observed in the separate EFECT treatment arms. After adjusting for major prognostic factors, sTKa remained an independent marker. CONCLUSION: sTKa is a potential circulating prognostic marker in patients with advanced breast cancer treated with endocrine therapy. It may also represent a tool for upfront identification of endocrine therapy resistance and early positive response to therapy. Independent validation of these results is warranted.

Clinical outcomes after palbociclib with or without endocrine therapy in postmenopausal women with hormone receptor positive and HER2-negative metastatic breast cancer enrolled in the TREnd trial.

Currently, there is limited data regarding the effectiveness of standard subsequent line therapies such as endocrine therapy, chemotherapy, or targeted agents after progression on CDK4/6 inhibitor-based regimens. This paper describes time-to-treatment failure beyond progression on palbociclib or palbociclib+endocrine therapy in patients enrolled in the phase II, multicenter TREnd trial. Our results indicate that there is limited benefit from post-palbociclib treatment, regardless of the type of therapy received. A small population of long responders were identified who demonstrated ongoing benefit from a subsequent line of endocrine therapy after progression to palbociclib-based regimens. A translational research program is ongoing on this population of outliers.

Platinum-based Agent and Fluorouracil in Metastatic Breast Cancer: A Retrospective Monocentric Study with a Review of the Literature.

BACKGROUND: The combination of platinum with 5-fluorouracil has scarcely been studied in metastatic breast cancer. As this combination does not lead to significant hepatic metabolism, in some clinical situations it may prove useful, especially in cases with liver dysfunction and an urgent clinical need for rapid tumor shrinkage. A retrospective study was conducted to evaluate the efficacy and safety of the combination of cisplatin and 5-fluorouracil in patients with metastatic breast cancer with significant alterations of biochemistry. PATIENTS AND METHODS: A total of 109 patients with metastatic breast cancer and liver dysfunction were treated; time-to-progression, overall survival and trends in liver function were evaluated. RESULTS: The median time-to-progression was 3.4 months, and median overall survival was 7.8 months. About 50% of patients obtained a complete, partial or stable biochemical response and 24 patients were subsequently able to receive additional therapies. CONCLUSION: Our results show that this therapeutic doublet represents a clinically effective, safe and well-tolerated treatment option for patients with metastatic breast cancer and liver dysfunction.

The role of abemaciclib in treatment of advanced breast cancer.

Until recently, the mainstay of treatment in the majority of hormone receptor (HR)-positive, human epidermal growth factor 2 receptor (HER2)-negative advanced breast cancer (ABC) has consisted of single-agent endocrine therapy (ET). However, as understanding of endocrine resistance has grown, newer targeted agents have come to the fore. Inhibition of cyclin-dependent kinase complexes 4 and 6 (CDK4/6) combined with ET has shown significant activity in HR+ HER2- ABC, with impressive results in terms of progression-free survival (PFS) when compared with ET alone. This review summarizes the seminal findings pertaining to CDK4/6 inhibition in this population, specifically focusing on abemaciclib, contrasted with palbociclib and ribociclib. Potential directions for future studies are discussed, as a way of addressing outstanding issues such as establishing optimal treatment sequencing and agent combinations, appropriate patient selection to derive maximal benefits, predictive biomarkers and the employment of CDK4/6 inhibition beyond the ABC setting.

Plasma thymidine kinase-1 activity predicts outcome in patients with hormone receptor positive and HER2 negative metastatic breast cancer treated with endocrine therapy.

The aim of this study was to investigate if thymidine kinase-1 (TK1), a well-known proliferation marker, could represent a valid circulating biomarker to identify hormone receptor positive (HR+)/HER2 negative (HER2neg) metastatic breast cancer (MBC) patients most likely to benefit from endocrine therapy (ET). We used the DiviTum™ assay to analyze TK1 activity in cell lysates of three HR+/HER2neg BC cell lines and in plasma of 31 HR+/HER2neg MBC patients receiving ET. Blood samples were collected at treatment initiation, after one month and at disease progression. CTCs count and ESR1/PIK3CA mutations in circulating tumor DNA were performed and correlated with TK1 activity. TK1 activity was reduced in the two endocrine-sensitive cell lines after 2 days of treatment. In patients, high baseline TK1 activity correlated with CTCs positivity (p-value=0.014). Patients with low baseline levels of TK1 activity had a significantly better PFS compared to those with high baseline TK1 activity (p-value=0.012). Patients with an early drop of TK1 activity after one month of treatment had a significantly better PFS compared to those who experienced an increase (p-value=0.0026). Our study suggests that TK1 could be a potential prognostic, predictive and monitoring marker of early ET response in HR+/HER2neg MBC patients.

Mutational analysis of single circulating tumor cells by next generation sequencing in metastatic breast cancer.

Circulating Tumor Cells (CTCs) represent a "liquid biopsy" of the tumor potentially allowing real-time monitoring of cancer biology and therapies in individual patients.The purpose of the study was to explore the applicability of a protocol for the molecular characterization of single CTCs by Next Generation Sequencing (NGS) in order to investigate cell heterogeneity and provide a tool for a personalized medicine approach.CTCs were enriched and enumerated by CellSearch in blood from four metastatic breast cancer patients and singularly isolated by DEPArray. Upon whole genome amplification 3-5 single CTCs per patient were analyzed by NGS for 50 cancer-related genes.We found 51 sequence variants in 25 genes. We observed inter- and intra-patient heterogeneity in the mutational status of CTCs.The highest number of somatic deleterious mutations was found in the gene TP53, whose mutation is associated with adverse prognosis in breast cancer.The discordance between the mutational status of the primary tumor and CTCs observed in 3 patients suggests that, in advanced stages of cancer, CTC characteristics are more closely linked to the dynamic modifications of the disease status.In one patient the mutational profiles of CTCs before and during treatment shared only few sequence variants.This study supports the applicability of a non-invasive approach based on the liquid biopsy in metastatic breast cancer patients which, in perspective, should allow investigating the clonal evolution of the tumor for the development of new therapeutic strategies in precision medicine.

Using CTCs for pharmacogenomic analysis.

In the era of precision medicine in oncology, pharmacogenomic assessment is a vital step in delivering personalized care. Increasing evidence points towards the importance of assessing molecular features of the advanced disease, rather than relying on the primary tumor sample, in order to appreciate the evolution of the tumor and to target relevant features. Circulating tumor cells (CTCs) represent a novel method of tumor sampling, as they offer a contemporaneous picture of the current disease state without the need for invasive needle biopsy. As they may derive from any number of metastatic sites, the potential to capture the heterogeneity of the disease is increased. Improvements in CTC capture, enrichment and isolation technology now allow sophisticated interrogation of these cells, such that pharmacogenomic assessment of CTCs is now possible, and the clinical potential is being explored. We review current and potential uses for CTCs for pharmacogenomic analysis.

Feasibility of a workflow for the molecular characterization of single cells by next generation sequencing.

The purpose of the study was to explore the feasibility of a protocol for the isolation and molecular characterization of single circulating tumor cells (CTCs) from cancer patients using a single-cell next generation sequencing (NGS) approach. To reach this goal we used as a model an artificial sample obtained by spiking a breast cancer cell line (MDA-MB-231) into the blood of a healthy donor. Tumor cells were enriched and enumerated by CellSearch(®) and subsequently isolated by DEPArray™ to obtain single or pooled pure samples to be submitted to the analysis of the mutational status of multiple genes involved in cancer. Upon whole genome amplification, samples were analysed by NGS on the Ion Torrent PGM™ system (Life Technologies) using the Ion AmpliSeq™ Cancer Hotspot Panel v2 (Life Technologies), designed to investigate genomic "hot spot" regions of 50 oncogenes and tumor suppressor genes. We successfully sequenced five single cells, a pool of 5 cells and DNA from a cellular pellet of the same cell line with a mean depth of the sequencing reaction ranging from 1581 to 3479 reads. We found 27 sequence variants in 18 genes, 15 of which already reported in the COSMIC or dbSNP databases. We confirmed the presence of two somatic mutations, in the BRAF and TP53 gene, which had been already reported for this cells line, but also found new mutations and single nucleotide polymorphisms. Three variants were common to all the analysed samples, while 18 were present only in a single cell suggesting a high heterogeneity within the same cell line. This paper presents an optimized workflow for the molecular characterization of multiple genes in single cells by NGS. The described pipeline can be easily transferred to the study of single CTCs from oncologic patients.

Heterogeneity of PIK3CA mutational status at the single cell level in circulating tumor cells from metastatic breast cancer patients.

Circulating Tumor Cells (CTCs) represent a "liquid biopsy of the tumor" which might allow real-time monitoring of cancer biology and therapies in individual patients. CTCs are extremely rare in the blood stream and their analysis is technically challenging. The CellSearch(®) system provides the enumeration of CTCs with prognostic significance in patients with metastatic breast cancer (mBC), but it does not allow their molecular characterization, which might be useful to identify therapeutically relevant targets for individualized treatment. Combining the CellSearch(®) and DEPArray™ technologies allows the recovery of single CTCs as a pure sample for molecular analysis. The purpose of the study was to investigate the heterogeneity of PIK3CA mutational status within single CTCs isolated from individual mBC patients. CTCs were enriched and enumerated by CellSearch(®) in blood samples collected from 39 mBC patients. In 20 out of 39 patients enriched samples with ≥5 CTCs were sorted using DEParray™ to isolate single CTCs or pools of CTCs to be submitted to Whole Genome Amplification (WGA) before sequencing analysis. In 18 out of 20 patients, it was possible to perform PIK3CA sequencing on exons 9 and 20. Twelve subjects were wild type (wt) for the PIK3CA gene. PIK3CA status could also be assessed in pools of CTCs in seven of these patients, with consistent wt status found. Six patients (33%) had a PIK3CA mutation identified. In 2 of the six patients, molecular heterogeneity was detected when mutational analysis was performed on more than one single CTC, including one patient with loss of heterozygosity on both single and pooled CTCs, and one patient with three different PIK3CA variants on single CTCs but PIK3CA wt status on pooled CTC samples. In six out of the 18 cases PIK3CA status was also evaluable on a primary tumor sample. In one of the six cases a discordance in PIK3CA status between the primary (wild-type) and the matched CTC (exon 20 mutation) was observed. This study demonstrates the feasibility of a non-invasive approach based on the liquid biopsy in mBC patients. Moreover, our data suggest the importance of characterizing CTCs at the single cell level in order to investigate the molecular heterogeneity within cells from the same patient.

International study on inter-reader variability for circulating tumor cells in breast cancer.

INTRODUCTION: Circulating tumor cells (CTCs) have been studied in breast cancer with the CellSearch® system. Given the low CTC counts in non-metastatic breast cancer, it is important to evaluate the inter-reader agreement. METHODS: CellSearch® images (N = 272) of either CTCs or white blood cells or artifacts from 109 non-metastatic (M0) and 22 metastatic (M1) breast cancer patients from reported studies were sent to 22 readers from 15 academic laboratories and 8 readers from two Veridex laboratories. Each image was scored as No CTC vs CTC HER2- vs CTC HER2+. The 8 Veridex readers were summarized to a Veridex Consensus (VC) to compare each academic reader using % agreement and kappa (κ) statistics. Agreement was compared according to disease stage and CTC counts using the Wilcoxon signed rank test. RESULTS: For CTC definition (No CTC vs CTC), the median agreement between academic readers and VC was 92% (range 69 to 97%) with a median κ of 0.83 (range 0.37 to 0.93). Lower agreement was observed in images from M0 (median 91%, range 70 to 96%) compared to M1 (median 98%, range 64 to 100%) patients (P < 0.001) and from M0 and <3CTCs (median 87%, range 66 to 95%) compared to M0 and ≥3CTCs samples (median 95%, range 77 to 99%), (P < 0.001). For CTC HER2 expression (HER2- vs HER2+), the median agreement was 87% (range 51 to 95%) with a median κ of 0.74 (range 0.25 to 0.90). CONCLUSIONS: The inter-reader agreement for CTC definition was high. Reduced agreement was observed in M0 patients with low CTC counts. Continuous training and independent image review are required.

Can biomarker assessment on circulating tumor cells help direct therapy in metastatic breast cancer?

Circulating tumor cell (CTC) count has prognostic significance in metastatic breast cancer, but the predictive utility of CTCs is uncertain. Molecular studies on CTCs have often been limited by a low number of CTCs isolated from a high background of leukocytes. Improved enrichment techniques are now allowing molecular characterisation of single CTCs, whereby molecular markers on single CTCs may provide a real-time assessment of tumor biomarker status from a blood test or "liquid biopsy", potentially negating the need for a more invasive tissue biopsy. The predictive ability of CTC biomarker analysis has predominantly been assessed in relation to HER2, with variable and inconclusive results. Limited data exist for other biomarkers, such as the estrogen receptor. In addition to the need to define and validate the most accurate and reproducible method for CTC molecular analysis, the clinical relevance of biomarkers, including gain of HER2 on CTC after HER2 negative primary breast cancer, remains uncertain. This review summarises the currently available data relating to biomarker evaluation on CTCs and its role in directing management in metastatic breast cancer, discusses limitations, and outlines measures that may enable future development of this approach.

The continued evidence from overviews: what is the clinical utility?

The Oxford Overview process has provided us with extremely high-powered meta-analyses assessing the role of adjuvant chemotherapy in early breast cancer. From the most recent publication, the proportional benefits from chemotherapy are relatively equivalent across all patient subgroups, a finding contradictory to our growing understanding of the role of tumour biology in dictating chemosensitivity. Several factors, including heterogeneity of patient groups and chemotherapy regimens, lack of data on underlying tumour biological subtypes, and confounding effect of chemotherapy-induced ovarian suppression in premenopausal women with hormone receptor positive breast cancer, impact on the applicability and clinical utility of the Overview in current and future oncological practice. With these considerations, the Overview has become less clinically relevant as a tool for guiding adjuvant chemotherapy treatment decisions, and a new direction is required.

Adjuvant chemotherapy: which patient? What regimen?

In the past, treatment decisions regarding adjuvant chemotherapy in early breast cancer (EBC) were made solely based on clinicopathologic factors. However, with increased awareness of the importance of underlying tumor biology, we are now able to use genomic analyses to determine molecular breast cancer subtype and thus identify patients with tumors that are chemotherapy resistant and unlikely to benefit from the addition of chemotherapy. Although genomics has allowed some patients to avoid chemotherapy-specifically those with luminal A-like breast cancer-these assays do not indicate which regimen is most appropriate. For this, consideration must be given to the combination of underlying tumor biology, tumor stage, and patient characteristics, such as age and tolerability of side effects.

The efficacy of lapatinib in metastatic breast cancer with HER2 non-amplified primary tumors and EGFR positive circulating tumor cells: a proof-of-concept study.

BACKGROUND: Analysis of circulating tumor cells (CTCs) provides real-time measures of cancer sub-populations with potential for CTC-directed therapeutics. We examined whether lapatinib which binds both HER2 and EGFR could induce depletion of the EGFR-positive pool of CTCs, which may in turn lead to clinical benefits. PATIENTS AND METHODS: Patients with metastatic breast cancer and HER2 non-amplified primary tumors with EGFR-positive CTCs were recruited and lapatinib 1500 mg daily was administered, in a standard two step phase 2 trial. RESULTS: There were no responses leading to termination at the first analysis with 16 patients recruited out of 43 screened. In 6 out of 14 (43%) individuals eligible for the efficacy analysis, a decrease in CTCs was observed with most of these having a greater decrease in their EGFR-positive CTC pool. CONCLUSIONS: This is one of the first studies of CTC-directed therapeutics and suggests that lapatinib monotherapy is not having any demonstrable clinical effects by reducing the EGFR-positive pool of CTCs in HER2 non-amplified primary tumors. Our attempt to expand the pool of patients eligible for a targeted therapy was unsuccessful; the role of clonal populations in cancer biology and therapeutic strategies to control them will require extensive evaluation in years to come. TRIAL REGISTRATION: Clinical trials.gov NCT00820924.

Final results of a multicenter phase II clinical trial evaluating the activity of single-agent lapatinib in patients with HER2-negative metastatic breast cancer and HER2-positive circulating tumor cells. A proof-of-concept study.

This multicenter phase II trial was designed to evaluate the activity of lapatinib in metastatic breast cancer patients with HER2-negative primary tumors and HER2-positive circulating tumor cells (CTCs). In this study MBC patients with HER2-negative primary tumors and HER2-positive CTCs previously treated with at least a first-line therapy for metastatic disease received lapatinib 1500 mg/day. The CellSearch System® was used for CTCs isolation and bio-characterization. HER2 status was assessed on CTCs by immunofluorescence. A case was defined as CTCs positive if ≥2 CTC/7.5 ml of blood were isolated and HER2-positive if ≥50% of CTCs were HER2-positive. 139 HER2-negative patients were screened, 96 patients were positive for CTCs (mean number of CTCs: 85; median number of CTCs: 19; range 2-1637). Seven of the 96 patients (7%) had ≥50% HER2-positive CTCs and were eligible for treatment with lapatinib. No objective tumor responses occurred in this population. In one patient, disease stabilization lasting 254 days (8.5 months) was observed. From the findings of this study, we concluded that a subset of patients with a HER2-negative primary tumor presents HER2-positive CTCs during disease progression, although the HER2 shift rate seems to be lower than previously reported. Despite the lack of objective response, the durable disease stabilization observed in one patient cannot rule out the hypothesis that lapatinib may have some activity in this patient population. However, considering that only 1/139 screened patients may potentially have derived benefit from this approach, future trials designed according to the presented strategy cannot be recommended.

HER2-positive circulating tumor cells in breast cancer.

PURPOSE: Circulating Tumor Cells (CTCs) detection and phenotyping are currently evaluated in Breast Cancer (BC). Tumor cell dissemination has been suggested to occur early in BC progression. To interrogate dissemination in BC, we studied CTCs and HER2 expression on CTCs across the spectrum of BC staging. METHODS: Spiking experiments with 6 BC cell lines were performed and blood samples from healthy women and women with BC were analyzed for HER2-positive CTCs using the CellSearch®. RESULTS: Based on BC cell lines experiments, HER2-positive CTCs were defined as CTCs with HER2 immunofluorescence intensity that was at least 2.5 times higher than the background. No HER2-positive CTC was detected in 42 women without BC (95% confidence interval (CI) 0-8.4%) whereas 4.1% (95%CI 1.4-11.4%) of 73 patients with ductal/lobular carcinoma in situ (DCIS/LCIS) had 1 HER2-positive CTC/22.5 mL, 7.9%, (95%CI 4.1-14.9%) of 101 women with non metastatic (M0) BC had ≥1 HER2-positive CTC/22.5 mL (median 1 cell, range 1-3 cells) and 35.9% (95%CI 22.7-51.9%) of 39 patients with metastatic BC had ≥1 HER2-positive CTC/7.5 mL (median 1.5 cells, range 1-42 cells). In CTC-positive women with DCIS/LCIS or M0 BC, HER2-positive CTCs were more commonly detected in HER2-positive (5 of 5 women) than HER2-negative BC (5 of 12 women) (p = 0.03). CONCLUSION: HER2-positive CTCs were detected in DCIS/LCIS or M0 BC irrespective of the primary tumor HER2 status. Nevertheless, their presence was more common in women with HER2-positive disease. Monitoring of HER2 expression on CTCs might be useful in trials with anti-HER2 therapies.