Negative Circulating Tumor Cells Research Articles

Real-world use of a CSF circulating tumor cell assay in the diagnosis and management of leptomeningeal metastasis.

2029 Background: The diagnosis of leptomeningeal metastasis (LM) can be challenging due to variability in clinical symptoms, radiographic, and cerebrospinal fluid (CSF) findings. The National Comprehensive Cancer Network (NCCN) guidelines recommend assessment of circulating tumor DNA (ctDNA) to increase sensitivity of tumor cell detection and assess the response to treatment. We hypothesize that the real-world use of an assay for the direct detection and enumeration of circulating tumor cells (CTCs) in the CSF is clinically useful for accurate diagnosis of LM, particularly in an early stage of disease. Methods: We report a series of 55 patients treated at our institution with a cancer diagnosis and either neurological symptoms or radiographic findings that suggested LM. All patients underwent a lumbar puncture, assessment for CSF CTCs, and conventional hospital-based cytology testing between 6/1/2020 and 8/1/2023. Survival data cutoff was 12/31/2023. Patient outcomes are reported. Results: 55 patients were tested, and 30 patients were found to be positive for CTCs and diagnosed with LM. Only 10 patients were concurrently positive for CTCs and cytology at our institution, whereas 20 patients with positive CTCs had a negative or ambiguous cytology. No patients with a negative CTC result (25 patients) were subsequently diagnosed with LM, whereas 4 patients with a positive CTC result remained without progressive neurological symptoms. 5 patients diagnosed with LM were alive at the time of data cutoff. The histologic breakdown for LM was: breast (11), non-small cell lung cancer (NSCLC) (16), gastrointestinal (GI) (3). Median overall survival (OS) was longer in patients with a positive CTC and negative cytology result compared to patients with concurrent positive CTC and cytology (172 vs. 63 days, p = 0.06). Median OS was also longer in breast cancer LM compared to NSCLC LM (235 vs. 63 days, p = 0.008). Most patients diagnosed with LM received therapies including Ommaya reservoir placement, intrathecal chemotherapy, and/or radiation. Conclusions: The use of a CSF circulating tumor cell assay aided the diagnosis of LM and led to timely initiation of treatment. A negative result of the CTC assay was associated with ruling out LM. Diagnosis of LM with the CTC assay and negative cytology was associated with longer survival, possibly due to earlier treatment initiation, and not solely a lead time bias. Breast cancer LM patients had improved survival compared to NSCLC and GI cancer patients, possibly due to more effective treatment options.

Presence of molecular residual disease after pathologic complete response among patients with inflammatory breast cancer.

3044 Background: Inflammatory breast cancer (IBC) is known to recur more frequently than non-IBC after pathologic complete response (pCR). The presence of circulating tumor cells (CTCs), a marker of molecular residual disease (MRD), has been associated with higher likelihood of metastasis. We sought to characterize CTCs and its relationship with pCR in IBC patients. Methods: Patients diagnosed with IBC were enrolled in a prospective registry from 2005-2022. Serial blood draws were performed before, during, and after neoadjuvant systemic therapy (NST), and 6-months and 1-year post-surgery. CTCs were enumerated using CellSearch™. Patients with ≥ 1 CTC at any timepoint in the post-operative period were included in the positive CTC cohort. T-tests, one-way ANOVA, and chi-squared tests were used to compare differences between groups. Kaplan-Meier analysis was used for survival outcomes. Results: A total of 112 patients were included. The median age of diagnosis was 50.5 years (IQR 17) and BMI was 29.3 kg/m2 (IQR 11.3). Patients were predominantly White (85, 75.9%) with clinical stage IIIB-C (94, 84.9%), node-positive (107, 95.5%), and HER2-negative (66, 59.0%) disease. Almost all patients (109, 97.3%) received trimodality therapy – NST, modified radical mastectomy, and adjuvant radiation. At a median follow-up period of 7.1 years (95% CI: 4.7-9.4), the overall survival (OS) rate was 72.3%. Baseline CTC positivity rate was 61.8% (42/68). More than half of the patients (61, 54.5%) had a positive CTC at some point in the post-operative surveillance period. Among the 39 patients who achieved pCR (34.8%), 15 (38.5%) had positive CTCs during follow-up. There were no differences in age, BMI, menopause status, clinical stage, nodal status, grade, presence of LVI, and number of lymph nodes (LNs) removed by CTC status. However, patients with positive CTCs had a significantly higher number of positive LNs at resection (p = 0.01), were more likely to be HER2-negative (p = 0.001), and were less likely to achieve pCR (p = 0.01). Triple negative disease (p < 0.0001), lack of pCR (p = 0.006), and positive CTCs (0.007) were associated with poor prognosis. When pCR was combined with CTC status, patients with positive CTCs demonstrated significantly worse survival, despite having achieved pCR, compared to those with pCR and negative CTC status (5-year OS: 35.0% vs. 83.1%, respectively, p = 0.016). Conclusions: A high proportion of IBC patients who achieved pCR had MRD, as demonstrated by persistent CTCs. CTCs portended worse prognosis in patients with IBC, even after pCR. Future incorporation of longitudinal CTC monitoring may be helpful in identifying patients at risk for relapse despite having achieved a pCR. [Table: see text]

Abstract 7043: Genomic profiling of DLL3-positive and negative CTCs in small cell lung cancer

Abstract BACKGROUND: Delta-like ligand 3 (DLL3), an atypical Notch family protein implicated in neuroendocrine tumorigenesis, has emerged as a promising therapeutic target in small cell lung cancer (SCLC), prompting numerous clinical trials investigating DLL3-targeted treatments. Exploring DLL3 in circulating tumor cells (CTCs) through liquid biopsy, coupled with comprehensive genomic analysis, presents an invaluable and minimally-invasive avenue for monitoring disease progression. This approach holds the potential to tailor personalized treatment strategies, emphasizing the critical need for in-depth investigations into both DLL3-positive and negative cell genomic compositions. METHODS: This study examined blood collected in CellSave preservative tubes from stage I (n=17) and stage IV (n=12) SCLC patients, as well as healthy donors (n=10). The CELLSEARCH® platform was employed to count EpCAM-enriched CTCs and evaluate DLL3 protein expression. Subsequently, individual CTCs were isolated based on the presence and absence of DLL3 expression using the DEPArray™ PLUS. The isolated DLL3-negative and positive CTCs were subjected to low-pass sequencing using the Ampli1™ LowPass Kit to uncover genomic aberrations. RESULTS: CTCs were absent in the healthy control group. In stage I patients, CTCs were identified in 5.8% of blood samples, while in stage IV patients, they were present in 50% of samples, with an average CTC count of 148 in stage IV. Among a total of 2074 detected CTCs, 460 were DLL3-positive, accounting for 6-28% of EpCAM-enriched CTCs in individual patients. Analysis of >300 copy number alteration (CNA) profiles of sorted single cells revealed considerable inter-patient and intra-patient heterogeneity, delineating recurrent clonality and specific genomic alterations in DLL3-negative CTCs. In contrast, DLL3-positive cells showed more stochastic CNA profiles, suggestive of apoptosis-related DNA fragmentation. CONCLUSIONS: Integrating CellSearch, DEPArray, and low-pass sequencing provides a minimally-invasive approach to compare genomic characteristics in DLL3-positive and negative CTCs from SCLC patients. Extension of this approach to a larger patient cohort and employing machine learning algorithms will facilitate identification of patterns within diverse CNA profiles, improving patient stratification and predicting treatment responses for personalized therapeutic strategies in SCLC. Citation Format: Zoltan Simandi, Thai Bui, Alberto Ferrarini, Steven Hepburn, Richard G. Del Mastro. Genomic profiling of DLL3-positive and negative CTCs in small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7043.

Frequency and Prognostic Value of Circulating Tumor Cells in Cancer of Unknown Primary.

Cancer of unknown primary (CUP) is defined as a primary metastatic malignancy, in which the primary tumor remains elusive in spite of a comprehensive diagnostic workup. The frequency and prognostic value of circulating tumor cells (CTCs), which are considered to be the source of metastasis, has not yet been systematically evaluated in CUP. A total of 110 patients with a confirmed diagnosis of CUP according to the European Society for Medical Oncology (ESMO) guidelines, who presented to our clinic between July 2021 and May 2023, provided blood samples for CTC quantification using CellSearch methodology. CTC counts were correlated with demographic, clinical, and molecular data generated by comprehensive genomic profiling of tumor tissue. CTCs were detected in 26% of all patients at initial presentation to our department. The highest CTC frequency was observed among patients with unfavorable CUP (35.5%), while patients with single-site/oligometastatic CUP harbored the lowest CTC frequency (11.4%). No statistically significant association between CTC positivity and the number of affected organs (P = 0.478) or disease burden (P = 0.120) was found. High CTC levels (≥5 CTCs/7.5 mL; 12/95 analyzed patients) predicted for adverse overall survival compared to negative or low CTC counts (6-months overall survival rate 90% vs 32%, log-rank P < 0.001; HR 5.43; 95% CI 2.23-13.2). CTC dynamics were also prognostic for overall survival by landmark analysis (log-rank P < 0.001, HR 10.2, 95% CI 1.95-52.9). CTC frequency is a strong, independent predictor of survival in patients with CUP. CTC quantification provides a useful prognostic tool in the management of these patients.

Abstract B016: Liquid biopsy biomarker analysis of a phase II trial of sacituzumab govitecan in castrate resistant metastatic prostate cancer

Abstract Background: Sacituzumab Govitecan (SG) is an antibody-drug conjugate targeting Trop-2 and has been approved for use in breast and bladder cancers. Trop-2 has been shown to be overexpressed in multiple solid tumors including prostate cancer. Here we report an interim analysis of longitudinal liquid biopsies collected in a phase II clinical trial of SG to identify biomarkers of response and resistance. Methods: We collected longitudinal blood samples from 20 patients for circulating tumor cell (CTC) and cell-free DNA (cfDNA) analysis as part of an open label Phase II trial of SG in patients with mCRPC (ClinicalTrials.gov Identifier: NCT03725761). Eligibility criteria for the trial included rising PSA and radiographic progression on abiraterone acetate or enzalutamide in the mCRPC setting. Liquid biopsies were collected at baseline, C1D8, and then every 3 cycles until disease progression. cfDNA was sequenced using a custom 822 gene targeted capture panel (IDT). CTCs were isolated with antibodies to either EpCAM or Trop-2 followed by parallel enumeration, EpCAM and Trop-2 protein phenotyping and RNA extraction for AR/NEPC marker transcriptional profiling. Results: Although no PSA50 responses were observed, the 6-month rPFS rate was 45% (64% in chemotherapy naïve patients). For this analysis, these patients will be termed responding patients. The number of Trop-2-postive CTCs at baseline was significantly higher in responding (24.3 ±13.4 per 7.5 mL blood) than non-responding (10.0±3.8) patients. During treatment the number of Trop-2 positive CTCs in responders significantly decreased by C3D1 to 10.0 ±3.8. Interestingly, while the number of Trop-2 positive CTCs continued to decline to 2.8±1.99 cells/7.5 mL, EpCAM-positive CTCs increased from 12.5±10.52 cells/7.5 mL to 23.2±19.49 at end of trial. Gene expression analysis demonstrated high expression of genes specific to adenocarcinoma including AR-splice variants, TMPRSS2, KLK2 and KLK3 in the majority of patients, with conversion to AR-variant negative CTCs identified in responders. Preliminary cfDNA analysis identified one patient with a mutation acquired in the gene encoding topoisomerase 1 (TOP1) upon progression on SG, with additional analysis ongoing. Conclusions: Patients who responded to SG had a more Trop-2 positive CTCs with adenocarcinoma characteristics with expression of AR pathway genes. Longitudinal analysis of liquid biopsy biomarkers identified multiple mechanisms of acquired SG resistance. Decline in Trop2-CTC population with parallel expansion of EpCAM-CTC population in multiple patients suggests loss of Trop2 surface protein expression as resistance mechanism, while identification of a cfDNA TOP1 mutation in one patient at time of progression is consistent with acquired resistance to the topoisomerase inhibitor payload as has been reported in metastatic triple negative breast cancer. Citation Format: Jamie M. Sperger, Amy K. Taylor, Yue Shi, Charlotte N. Stahlfeld, Kyle Helzer, Matthew Bootsma, Katherine R. Kaufmann, Marina N. Sharifi, Christos E. Kyriakopoulos, Susan Slovin, Scott Tagawa, Scott Dehm, Shuang G. Zhao, Joshua M. Lang. Liquid biopsy biomarker analysis of a phase II trial of sacituzumab govitecan in castrate resistant metastatic prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B016.

Bone scan index (BSI) scoring by using bone scintigraphy and circulating tumor cells (CTCs): predictive factors for enzalutamide effectiveness in patients with castration-resistant prostate cancer and bone metastases

Reports of Bone Scan Index (BSI) calculations as imaging biomarkers to predict survival in patients with metastatic castration-resistant prostate cancer (mCRPC) have been mainly from retrospective studies. To evaluate the effectiveness of enzalutamide (ENZ) in Japanese patients with mCRPC and bone metastases using BSI (bone scintigraphy) and circulating tumor cell (CTC) analysis. Prospective, single-arm study at Juntendo University affiliated hospitals, Japan. Patients were administered 160 mg ENZ daily, with 3 monthly assessments: BSI, prostate specific antigen (PSA), CTC and androgen receptor splicing variant-7 (AR-V7) status. Primary endpoint: BSI-decreasing rate after ENZ treatment. Secondary endpoints: PSA-decreasing rate and progression free survival (PFS). Statistical analyses included the Wilcoxon t-test, Cox proportional hazard regression analysis, and log-rank test. Median observation period: 17.9 months, and median PFS: 13.8 (2.0–43.9) months (n = 90 patients). A decrease in BSI compared to baseline as best BSI change on ENZ treatment was evident in 69% patients at the end of the observation period (29% patients showed a complete response, BSI 0.00). At 3 months 67% patients showed a ≥ 50% PSA reduction, and 70% after ENZ treatment. PSA decline (3 months) significantly associated with a prolonged median PFS: 18.0 (estimated) versus 6.4 months (HR 2.977 [95% CI 1.53–5.78], p = 0.001). Best BSI decline response significantly associated with a prolonged PFS: 18.1(estimated) versus 7.8 months (HR 2.045 [95% CI: 1.07–3.90], p = 0.029). CTC negative status (n = 20) significantly associated with a prolonged PFS: 13.4 [estimated] vs 8.6 months (HR 2.366, 95% CI 0.97–5.71, p = 0.041). CTC positive/AR-V7 positive status significantly associated with a shorter PFS: 5.9 months (HR 8.56, 95% CI 2.40–30.43, p = 0.0087). -reduction (3 months) and BSI-reduction (on ENZ treatment) were significant response biomarkers, and a negative CTC status was a predictive factor for ENZ efficacy in patients with mCRPC.

Abstract P1-05-23: OPTIMIZING THE DIAGNOSIS OF LEPTOMENINGEAL METASTASES IN BREAST CANCER PATIENTS BY CIRCULATING TUMOR CELLS AND CIRCULATING TUMOR DNA

Abstract Introduction: Leptomeningeal metastases (LM) occur in approximately 5% of patients with breast cancer, negatively impacting their prognosis. Reliable diagnosis of LM is challenging, but timely diagnosis could lead to more treatment options and consequently a better prognosis. Circulating tumor DNA (ctDNA) and circulating tumor cells (CTCs) in cerebrospinal fluid (CSF) are potential methods to improve the diagnosis of LM. In this prospective study we compared cytology (current gold standard for CSF analysis in diagnosing LM) with CTC enumeration and ctDNA detection in CSF for diagnosing LM in patients with breast cancer. Methods: In a prospective study in patients with clinical suspicion of LM who were planned to undergo a diagnostic lumbar puncture (LP) for CSF cytology the presence of CTCs/ctDNA in CSF was compared to the presence of tumor cells in CSF by cytology. CTC enumeration was performed using the FDA approved CellSearch System (Menarini). The detection of ctDNA was performed using the mFAST-Seqs method, which detects aneuploidy throughout the genome by selective amplification of long interspaced nuclear element sequences (LINE-1 elements). In a control group consisting of 15 patients with a hematologic malignancy with suspicion of LM, 2 cases had 1 CTC in their CSF, therefore the cutoff for a positive CTC test was set at 2 CTCs. Results: In total 80 patients with breast cancer were included from January 2016 till January 2022. In 16 out of 80 patients CSF cytology was positive of whom 14 (87.5%) had a positive CTC test. From the 2 patients in which the CTC test was negative, one patient had 1 CTC detected in CSF and for both patients a lower volume of CSF was available for the CTC test compared to the volume used for cytology. In 2 of the 16 cytology positive patients, who underwent a second LP, CTCs were positive in the CSF from the first LP, while cytology was only positive in the CSF of the second LP. Of the 64 patients with a negative cytology, 7 (10.9%) patients had a positive CTC test. Two of these 7 patients had typical symptoms of LM, a suspicious MRI and a course of disease matching with LM according to the neuro-oncologist. Overall survival (OS) was shorter in patients with a positive CTC test compared to patients with a negative test (median OS: 19.2 months vs. 3.4 months, log-rank test, p=0.007). When only patients with a negative cytology were included in this analysis, OS remains significantly shorter in the group with a positive CTC test (n=7) compared to the group with the negative CTCs (n=57) (median OS 19.3 months vs. 3.5 months, long-rank test, p=0.003). Additionally, ctDNA detection in CSF was compared to CSF cytology in 51 patients, of which 11 had a positive CSF cytology result. For 8 of these 11 patients ctDNA was detected (72.2%) while 1 of the 40 patients with a negative cytology had ctDNA. Discussion: Both CTC enumeration and ctDNA detection can be used to detect LM in CSF. CTC detection could even improve timely diagnosis of LM in patients with breast cancer. However, the added value of ctDNA seems less evident. Citation Format: Elisabeth M Jongbloed, Lindsay Angus, Martin J van den Bent, Joost LM Jongen, John WM Martens, Ngoc M Van, Vanja de Weerd, Carolien HM van Deurzen, Jaco Kraan, Saskia M Wilting, Agnes Jager. OPTIMIZING THE DIAGNOSIS OF LEPTOMENINGEAL METASTASES IN BREAST CANCER PATIENTS BY CIRCULATING TUMOR CELLS AND CIRCULATING TUMOR DNA [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-05-23.

Circulating tumor cells dynamics during chemotherapy predict survival and response in advanced non-small-cell lung cancer patients.

Circulating tumor cells (CTCs) are prognostic biomarker in non-small-cell lung cancer (NSCLC). CTCs could also be used as predictor of efficacy of systemic treatments in advanced NSCLC. We described the dynamic changes of CTCs during first-line platinum-based chemotherapy in advanced NSCLC and clarified the correlation between CTC counts and efficacy of chemotherapy. Chemotherapy is administered and blood specimens are collected at four time points from baseline to disease progression for CTC detection. This multicenter prospective study enrolled patients with previously untreated stage III or IV NSCLC fit for standard platinum-based chemotherapy. Bloods were sampled as per standard operating procedures at baseline, cycle 1 and cycle 4 of chemotherapy, and at disease progression for CTC analysis using the CellSearch system. Among 150 patients enrolled, median overall survival (OS) was 13.8, 8.4, and 7.9 months in patients with CTC-, KIT-CTC, and KIT+CTC at baseline (p = 0.002). Patients with persistent negative CTC (46.0%) had longer progression-free survival [5.7 months, 95% confidence interval (CI): 5.0-6.5 versus 3.0 months, 0.6-5.4; hazard ratio (HR): 0.34, 95% CI: 0.18-0.67) and OS (13.1 months, 10.9-15.3 versus 5.6 months, 4.1-7.1; HR: 0.17, 0.08-0.36) compared with patients with persistent positive CTC (10.7%), which was not impacted by chemotherapy. Chemotherapy decreased CTC from 36.0% (54/150) to 13.7% (13/95). CTC persistent presence during treatment represents poor prognosis and resistance to chemotherapy in advanced NSCLC. Chemotherapy could effectively eliminate CTCs. Molecular characterization and the functionalization of CTC will be warranted for further intensive investigation. NCT01740804.

Circulating Tumor Cells as a Predictive Biomarker in Resectable Lung Cancer: A Systematic Review and Meta-Analysis.

In breast, prostate, and other epithelial tumors, circulating tumor cells (CTC) in peripheral blood may predict survival. Our study evaluated the prognostic significance of baseline and postoperative CTC in patients with early non-small cell lung cancer (NSCLC) through a meta-analytic approach. Prospective studies comparing survival outcomes between positive (CTC+) and negative CTC (CTC-) patients were systematically searched. Primary outcomes were overall (OS) and disease-free survival (DFS) with hazard ratio (HR) and 95% confidence interval (CI) as the effect measure. Pooled HR determined the prognostic role under a fixed-effect or random-effect model depending on heterogeneity. Eighteen studies with 1321 patients were eligible. CTC+ patients were associated with an increased risk of death (HR 3.53, 95% CI 2.51-4.95; p &lt; 0.00001) and relapse (HR 2.97, 95% CI 2.08-4.22; p &lt; 0.00001). Subgroup analysis results were consistent in different subsets, including time points (baseline and postoperative) and sources (peripheral and pulmonary vein) of blood collection, detection methods (label-free, label-dependent, and RT-PCR), and follow-up duration. Our meta-analysis revealed that CTC is a promising predictive biomarker for stratifying survival outcomes in patients with early-stage NSCLC. However, future studies are required to validate these findings and standardize detection methods.

Correlation between circulating tumor cells and different molecular biological characteristics in breast cancer patients.

This study sought to detect the number of circulating tumor cells (CTCs) in breast cancer patients, and examine the relationship between CTCs and molecular biological characteristics. From June 2016 to June 2018, 150 female patients with invasive breast cancer detected by CTCs at the Department of Breast Surgery, Fudan University Cancer Hospital were enrolled in this study. The patients had an average age of 52.6±7.8 (range, 35-77) years. Routine pathological and immunohistochemical examinations were performed on tissues obtained during surgery. In this study, CTCs were detected using the immunomagnetic bead negative enrichment technique (i.e., the Cyttel technique). The measurement data are expressed by x ± s, and were compared by t-tests. A univariate analysis of variance was used to compare differences between groups. The count data are expressed as the absolute value, and the test χ2 or Fisher's exact test were used to compare differences. There were 109 cases of positive CTC (≥3 CTCs/4 mL) (72.7%), and 41 cases of negative CTC (<3 CTCs/4 mL) (27.3%). There were no significant differences in terms of age and menopausal status between the two groups (P>0.05). There was no significant difference in the positive rate of CTC in T1, T2, and T3 and above patients (P>0.05). There was no significant difference in the CTC positive rate between ER positive and negative patients, PR positive and negative patients, and Ki-67 ≥14% and <14% patients (P>0.05). However, there was a statistical difference in the positive rate of CTC between human epidermal growth factor receptor 2 (HER-2) positive and negative patients (P<0.05). There was no significant difference in the CTC positive rate among patients with Luminal A type, B type, HER-2 overexpression type, and triple negative breast cancer (TNBC) (P>0.05). There was no significant difference in the positive rate of CTC among patients with invasive ductal carcinoma, invasive lobular carcinoma, and other types of invasive carcinoma (P>0.05). It can be concluded that there is a relationship between CTC and HER-2 expression, which has certain predictive value for patients with positive HER-2 expression, thus predicting poor prognosis.

Integration of Deep Learning Radiomics and Counts of Circulating Tumor Cells Improves Prediction of Outcomes of Early Stage NSCLC Patients Treated With Stereotactic Body Radiation Therapy

We develop a deep learning (DL) radiomics model and integrate it with circulating tumor cell (CTC) counts as a clinically useful prognostic marker for predicting recurrence outcomes of early-stage (ES) non-small cell lung cancer (NSCLC) patients treated with stereotactic body radiation therapy (SBRT). A cohort of 421 NSCLC patients was used to train a DL model for gleaning informative imaging features from computed tomography (CT) data. The learned imaging features were optimized on a cohort of 98 ES-NSCLC patients treated with SBRT for predicting individual patient recurrence risks by building DL models on CT data and clinical measures. These DL models were validated on the third cohort of 60 ES-NSCLC patients treated with SBRT to predict recurrent risks and stratify patients into subgroups with distinct outcomes in conjunction with CTC counts. The DL model obtained a concordance-index of 0.880 (95% confidence interval, 0.879-0.881). Patient subgroups with low and high DL risk scores had significantly different recurrence outcomes (P = 3.5e-04). The integration of DL risk scores and CTC measures identified 4 subgroups of patients with significantly different risks of recurrence (χ2 = 20.11, P = 1.6e-04). Patients with positive CTC measures were associated with increased risks of recurrence that were significantly different from patients with negative CTC measures (P = 0.0447). In this first-ever study integrating DL radiomics models and CTC counts, our results suggested that this integration improves patient stratification compared with either imagining data or CTC measures alone in predicting recurrence outcomes for patients treated with SBRT for ES-NSCLC.

Circulating tumor cells counts are associated with CD8+ T cell levels in programmed death-ligand 1-negative non-small cell lung cancer patients after radiotherapy: A retrospective study.

This study aimed to explore the dynamics of circulating tumor cells (CTCs) and CD8+ T cells in stage II–III non-small cell lung cancer patients with CTCs in different programmed death-ligand 1 (PD-L1) status treated with radiotherapy and evaluate the correlation between CTCs and CD8+ T cells.This study was a retrospective study which reviewed 69 stage II–III non-small cell lung cancer patients underwent postoperative radiotherapy and peripheral blood tests of CTCs and T lymphocyte were available before radiation, 1 week after radiation and 1 month after radiation.In this study, 25 patients had PD-L1 positive CTCs and 44 patients had PD-L1 negative CTCs. The CTCs count was significantly decreased compared with baseline in patients with different PD-L1 status CTCs at 1 week and 1 month after radiotherapy. The proportion of CD8+ T cells was significantly increased at 1 month after radiotherapy compared with baseline in the total population (mean change, 7.24 ± 2.12; P < .05) and patients with PD-L1 negative CTCs (mean change, 7.17 ± 2.65; P < .05). One month after radiotherapy, the proportion of CD8+ T cells was negatively correlated with the CTCs count in the total population (r = −0.255, P = .034) and PD-L1 negative patients (r = –0.330, P = .029). In patients with PD-L1 negative CTCs, the CTCs count 1 week after radiotherapy (hazard ratio, 0.150 [95% confidence intervals., 0.027–0.840], P = .031) and the proportion of CD8+ T cells 1 month after radiotherapy (hazard ratio, 7.961 [95% confidence intervals, 1.028–61.68], P = .047) were independent prognostic factors for disease recurrence.After radiotherapy, only PD-L1-negative patients had a significant increase in the CD8+ T cell levels, while it was negatively correlated with CTCs count and was an independent prognostic factors of disease recurrence.

Abstract 599: Investigation of PD-L1 expression in circulating tumor cells isolated using the Parsortix system in metastatic lung and breast cancer patients

Abstract Programmed death-ligand 1 (PD-L1) allows cancer cells to evade the host immune response when upregulated. PD-L1 antagonists have been shown to be effective immunotherapies. The FDA approved the PD-L1 inhibitor nivolumab for treatment of previously treated, non-responding metastatic non-small cell lung cancer (NSCLC) patients, independent of the PD-L1 status identified in tumour tissue, likely due to the controversial value of PD-L1 detection on tissue biopsy that may be out-of-date. Measurement of PD-L1 expression in circulating tumor cells (CTCs) may enable repeat testing to provide up-to-date PD-L1 status and the potential to monitor patients on these therapies. Whilst the epitope-dependent CELLSEARCH® system is the only technology FDA-cleared for the enumeration of CTCs, its application is limited to epithelial CTCs and has limited sensitivity in NSCLC. We developed a research use only assay for the characterisation of PD-L1 expression on CTCs isolated using the Parsortix® system, a label-independent microfluidic device that harvests CTCs of all phenotypes (epithelial and/or mesenchymal) based on size and compressibility. Peripheral blood (8 – 10mL) was drawn into K2EDTA tubes from 17 healthy volunteers, 17 metastatic breast cancer (MBC) patients and 18 metastatic NSCLC patients and processed on Parsortix systems within 24 hours. Harvested CTCs were cytospun and immunofluorescently stained for detection of cytokeratins and PD-L1. Slides were imaged using a BioView AllegroPlus imaging system.No CTCs were identified in the healthy volunteers, highlighting the specificity of the assay. CTCs (≥1) were identified in 70% of the MBC patients and 55% of the NSCLC patients. Importantly, the positivity rate observed in NSCLC patients was 2-fold higher than that in previously described studies using the CELLSEARCH system. A mean of 9 CTCs/tube of blood were identified in the CTC positive MBC patients, with a range of 1 – 128 CTCs. A mean of 11 CTCs/tube of blood were identified in the CTC positive NSCLC patients, with a range of 1 – 23 CTCs. CTC clusters, consisting of 3 – 45 cells per cluster, were observed in both NSCLC and MBC patients. High heterogeneity of PD-L1 expression was observed. The CTC positive patients were classified into three groups: patients with CTCs positive for both cytokeratins (CK+) and PD-L1 (36% in MBC and 40% in NSCLC), patients with a mixed population of CK+, PD-L1+/- CTCs (27% in MBC and 40% in NSCLC) and patients with CK+, PD-L1- CTCs only (36% in MBC and 20% in NSCLC).The optimized assay for detection of PD-L1 expression on CTCs allowed for the identification of PD-L1 positive and PD-L1 negative CTCs in a significant proportion of the NSCLC and MBC patients studied. The ability to isolate significant numbers of PD-L1 positive CTCs in blood lays the groundwork for development of dynamic PD-L1 monitoring to support personalized patient management. Citation Format: Mariacristina Ciccioli, Amy Davis, Ofure Alenkhe, Anne-Sophie Pailhes-Jimenez. Investigation of PD-L1 expression in circulating tumor cells isolated using the Parsortix system in metastatic lung and breast cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 599.

Abstract PS2-15: The HER2 circulating ratio to define HER2 expressing circulating tumor cells in advanced breast cancer

Abstract Background Currently, there are no validated data derived from prospective trials that demonstrate a benefit from anti-HER2 targeted therapy in HER2 negative advanced breast cancer (ABC) patients (pts) bearing HER2 expressing (HER2+) circulating tumor cells (CTCs). Although some retrospective studies suggest that a group of these pts could benefit from a target treatment, a substantial proportion of those will never respond. A better characterization of the HER2+ CTCs could improve the pts selection. We hypothesize that a high correlation between different HER2+ CTCs subgroups and the HER2 status on solid biopsy can predict the likelihood of response of the corresponding subgroup. Here we propose a simple algorithm to identify those HER2+ CTCs subgroups that have demonstrated a higher correlation with HER2+ positivity in the solid biopsy. Methods The IRB-approved study retrospectively analyzed blood samples at two different timepoints (before treatment and at the first evaluation) from 110 ABC pts treated at Northwestern University (Chicago, IL) between 2016 and 2019. CTCs were enumerated through CellSearch™ (Menarini Silicon Biosystems, Bologna, Italy), and characterized for HER2 expression using the CellSearch CXC Kit. HER2 expression in CTCs was defined and categorized in 4 different categories (0,1+,2+,3+) as previously reported (Riethdorf et al., 2010). Four different scores were assessed in their ability to predict a HER2 positive disease (based on metastases HER2 status). Score 0 (negative CTCs), Score 1 (1+ CTCs), Score 2 (2+ CTCs), Score 3 (3+ CTCs) and Score 4 (cHER2 ratio, defined as the sum of 2+ CTCs and 3+ CTCs divided by the total number of CTCs). The performance of these 4 different biomarkers was explored longitudinally through the Wilcoxon test. Results: Out of 110 pts, 49 showed a CTCs count ≥ 5 (stage IV aggressive). Among these pts, Score 0 was associated with a HER2 negative disease with an area under the ROC curve (AUC) of 0.14. No correlation was found between Score 1 and HER2 status (AUC 0.45). A marginally significant association was found in Score 2 and Score 3 (AUC respectively 0.67 and 0.64). A direct correlation was observed between Score 4 and Her2 status (AUC 0.73). The analysis performed on stage IV indolent patients showed a non-significant association among all 4 scores. Significant association was not found among the scores and molecular subtypes, only a numerical increase among HER2+ disease and Score 3 and Score 4 (respectively p=0.06 and p=0.1). The patients were observed longitudinally and a dynamic Score evaluation was performed. No significant changes were found among Score 1 and Score 2 at the two different timepoints (p= 0.35 and p=0.11). Both, Score 0 and Score 4 were significantly decreased among pts at the second timepoint (p=0.0019 and 0.006) Conclusions The data highlighted a strong performance of cHER2 ratio (score4) identifying a HER2 positive disease on tissue biopsy, comparable with the known ability of score0 (presence of only HER2 negative CTCs) to predict a HER2 negative tissue biopsy. Furthermore, the cHER2 ratio has proven to be dependent on the treatment administration, allowing to be considered as a predictive biomarker in future study, to gain a prospective validation. Citation Format: Paolo D'Amico, Lorenzo Gerratana, Ami Shah, Qiang Zhang, Andrew Davis, Youbin Zhang, Saya Jacob, Elena Vagia, Amir Behdad, Carolina Reduzzi, Giuseppe Curigliano, Massimo Cristofanilli. The HER2 circulating ratio to define HER2 expressing circulating tumor cells in advanced breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS2-15.

Abstract PD3-12: Efficacy of the tyrosine kinase inhibitor lapatinib in the treatment of patients with HER2-negative metastatic breast cancer and HER2-positive circulating tumor cells - results from the randomized phase III DETECT III trial

Abstract Background: It is well-known that tumor biology may change during the course of the disease due to clonal evolution, and such changes might have important implications for response to targeted treatments. Circulating tumor cells (CTCs) could serve as a real-time liquid biopsy to detect changes in tumor biology. It has been demonstrated that patients with HER2-negative metastatic breast cancer (MBC) may have discordant, HER2-positive CTCs in the peripheral blood. However, up to now there is no randomized clinical trial investigating whether treatment decisions based on CTC phenotype provide benefits in terms of improved outcome. The aim of the DETECT III study is to investigate whether patients with initially HER2-negative MBC and HER2-positive CTCs benefit from HER2-targeted therapy with the tyrosine kinase inhibitor lapatinib. In addition, the significance of CTCs as an early predictive marker for response to therapy will be analyzed. Methods: The randomized phase III DETECT III trial (NCT01619111) compares lapatinib in combination with standard therapy versus standard therapy alone in patients with initially HER2-negative MBC and HER2-positive CTCs. Efficacy of lapatinib treatment is evaluated by CTC clearance rate, progression-free survival (PFS) and overall survival (OS). In addition, we investigate the association between CTC results and both PFS and OS to assess the utility of CTCs as an early predictive marker for treatment response. CTC enumeration and phenotyping was performed using the CellSearch® technology (Menarini Silicon Biosystems; Bologna, Italy). Survival data are analyzed using log rank tests, univariable and adjusted multivariable cox regressions. Results: First results on CTC clearance rates, PFS and OS of 105 prospectively randomized patients will be presented. Conclusion: This first randomized clinical trial in breast cancer patients with treatment decisions being based on the phenotype of CTCs will show whether patients with HER2 negative MBC and HER2 positive CTCs benefit from additional HER2-targeted therapy with lapatinib. This finding might be increasingly important as novel HER2-targeted drugs become available. Citation Format: Tanja Fehm, Volkmar Mueller, Maggie Banys-Paluchowski, Peter A Fasching, Thomas WP Friedl, Andreas Hartkopf, Jens Huober, Christian Loehberg, Brigitte Rack, Sabine Riethdorf, Andreas Schneeweiss, Diethelm Wallwiener, Franziska Meier-Stiegen, Oliver Hoffmann, Lothar Müller, Pauline Wimberger, Eugen Ruckhaeberle, Jens Blohmer, Wolfgang Janni. Efficacy of the tyrosine kinase inhibitor lapatinib in the treatment of patients with HER2-negative metastatic breast cancer and HER2-positive circulating tumor cells - results from the randomized phase III DETECT III trial [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD3-12.

Abstract PS2-19: Circulating tumor cell (CTC) enumeration in a phase II trial of pazopanib in addition to endocrine therapy in patients with hormone resistant advanced breast cancer (ABC)

Abstract Background: CTCs are detectable in approximately 50% of pts with metastatic breast cancer, and elevated CTC levels are an independent negative prognostic factor. CTCs have been shown to play a valuable role in predicting outcomes in pts with ABC treated with chemotherapy or endocrine therapy. This phase II trial was conducted to evaluate the clinical benefit (CB) of pazopanib, a VEGF receptor tyrosine kinase inhibitor (TKI) combined with nonsteroidal aromatase inhibitors (NSAIs) in pts with ABC resistant to NSAIs. As an exploratory analysis, we hypothesized that CTC levels might be correlated with response to pazopanib plus endocrine therapy. Methods: Eligibility included postmenopausal women with hormone receptor positive (HR+) ABC and progressive disease after at least one month of NSAIs. Treatment was pazopanib 800 mg/day plus either letrozole or anastrozole. The primary endpoint was clinical benefit rate at 12 weeks (CBR12, wks). Secondary endpoints included progression free survival (PFS), safety, and the impact of pazopanib and NSAI on CTCs. A CBR of 20% was considered a clinically meaningful comparison to the expected CBR of &amp;lt;5% with continued NSAIs after PD. Blood samples were collected for CTC analysis at baseline, then every 4 wks while on treatment. The presence of CTCs was assessed using the FDA-cleared CellSearch System; CTCs were defined as EPCAM-positive, CD45-negative nucleated cells. Samples with 5 CTCs per 7.5 mLs of blood were considered CTC-positive. Results: 32 pts were enrolled; 28 are evaluable for study endpoints. The median age was 58 years (range: 41-77). Pts were heavily pre-treated, with a median of 2 prior hormone therapies (range 1-6) and 1 prior chemotherapy (range 0-8). 8 pts (28.6%) stopped treatment due to adverse events, and 6 pts progressed before wk 12. CBR12 was 46.4% (12 SD, 1 PR), and CBR24 was 25% (5 SD, 2 PR). Safety has been presented (ASCO 2020). Median PFS was 20 wks, and median PFS for pts with CBR12 was 24 wks. Five (22%) of 23 pts with CTC data were CTC-positive (5 CTC/7.5 mL). There was no significant association between CBR12 and CTC status at baseline, or between CBR12 and change in CTC status (baseline to 4 wks after initiation of treatment). 7 pts had non-CBR12 and CTC data; 4 pts (n=4/7; 57%) were CTC positive at either baseline, week 4 or both. 11 pts had CBR12 and CTC data; all patients were CTC negative at baseline and remained negative at 4 wks. 7 pts had PFS &amp;gt;6 months (24, 32, 36, 36, 48, 184 and 274 wks), and 6 had CTC data: all were CTC-negative at baseline and 4 wks, then remained negative at 12 wks. Based on baseline values only, CTC-positive pts had a shorter median PFS compared to CTC-negative pts, but the difference was not statistically significant (11 wks vs 14 wks, p=0.18). Persistently CTC negative patients had significantly longer PFS compared to patients who were CTC positive at any time during study treatment (36 wks vs 11 wks, p=0.01). Conclusions: The addition of pazopanib to NSAIs resulted in a CBR12 of 46.4%, and a CBR24 of 25% in pts with heavily pre-treated ABC resistant to NSAIs. These results support clinical efficacy of antiangiogenic TKI in HR+ ABC and suggest benefit in hormone resistant disease. Consistently negative CTCs correlated with response and response duration. PFS was significantly longer in patients who were consistently CTC negative, further defining the prognostic role of CTCs in HR+ ABC. (NCT01466972) Citation Format: Ozge Gumusay, Mark Jesus M. Magbanua, Melanie C. Majure, Travis Deal, Jonathan R. Renslo, Chiara A. Wabl, Michelle E. Melisko, A. Jo Chien, Andrei Goga, Mark M. Moasser, John W. Park, Jimmy Hwang, Hope S. Rugo. Circulating tumor cell (CTC) enumeration in a phase II trial of pazopanib in addition to endocrine therapy in patients with hormone resistant advanced breast cancer (ABC) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS2-19.

Abstract 780: Alpha tubulin and EMT-related molecules expressed in circulating tumor cells (CTCs) isolated from non-small cell lung cancer patients

Abstract Introduction: Vimentin (VIM) expression in CTCs is a poor prognostic factor for breast cancer patients. Furthermore, upregulation of alpha Tubulin (TUB) and Detyrosynated tubulin (GLU) in CTCs is related to patients' outcome. In the current study, we evaluated TUB, GLU and VIM in NSCLC cell lines and in patients' CTCs. Methods: Four NSCLC cell lines were used for the evaluation of our method. In addition, 60 patients with metastatic NSCLC before the initiation of any line of treatment, were enrolled in this study. Thirty-three patients' samples were taken prior to the 1st line treatment and 27 patients were enrolled before the initiation of ≥2 lines of treatment. CTCs were isolated using ISET platform and stained with pancytokeratin (CK)/CD45/TUB and CK/GLU/VIM antibodies. Samples were analyzed using confocal laser scanning microscopy. Results: In patients' samples, CK(+)/CD45(-) cells were observed in 90% (54 out of 60 patients). CTCs with high expression of TUB were detected in 62.96% (34/54) of the patients. Among the total isolated CTCs/patient, 30.57 % belonged to the (CK+TUB+CD45) phenotype. The rest of the CTCs presented with either low (31.2%) or no expression (24.8%) of TUB. Interestingly, 4.15% of the CTCs (only in advanced disease) belonged to (CK-TUB+CD45-) phenotype. The proportion of TUB low or negative CTCs was statistically higher in treatment-naïve compared to pre-treated patients (p= 0.004 and p=0.007, respectively) whereas the proportion of TUB high CTCs was increased in pre-treated compared to treatment-naïve patients (85.72% vs 64.52%), implying that these CTCs persist after chemotherapy. Further analysis revealed that patients with high TUB expression in their CTCs experienced shorter OS compared to patients with CTCs with low or no TUB expression (7 vs 14 months, respectively; p=0.023). GLU and VIM were also evaluated in the same cohort of patients. The frequency of the observed phenotypes were as follow: (CK-GLU-VIM-): 35.19% (19/54 patients), (CK+GLU+VIM+): 62.96% (34/54), (CK+GLU+VIM-): 16.67% (9/54) and (CK+GLU-VIM+): 72.22%. The last one was the most abundant subclone in treatment naïve patients 81.25% (26/32). Furthermore the most abundant phenotypes in advanced disease were the (CK+GLU-VIM-) 59.09% (13/22), (CK+GLU-VIM+) 59.09% (13/22) and (CK+ GLU+ VIM+): 54.55% (12/22). The expression of VIM in advanced patients was also related to poor OS (1 vs 10 months, p=0.010). Conclusions: In agreement to our previous results in breast cancer patients, current study also revealed that alpha-Tubulin, GLU and Vimentin are overexpressed in CTCs from NSCLC patients. In addition, the presence of TUB and/or VIM-positive CTCs is potentially related to poor patients' outcome. Citation Format: Galatea Kallergi, Spyridoula D. Katsarou, Anastasia Voumvouraki, Christos Stournaras, Stuart S. Martin, Vassilis Georgoulias. Alpha tubulin and EMT-related molecules expressed in circulating tumor cells (CTCs) isolated from non-small cell lung cancer patients [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 780.

The Combination of Immunomagnetic Bead-Based Cell Isolation and Optically Induced Dielectrophoresis (ODEP)-Based Microfluidic Device for the Negative Selection-Based Isolation of Circulating Tumor Cells (CTCs).

Negative selection-based circulating tumor cell (CTC) isolation is able to harvest viable, label-free, and clinically meaningful CTCs from the cancer patients’ blood. Nevertheless, its main shortcoming is its inability to isolate high-purity CTCs, restricting subsequent CTC-related analysis. To address this issue, this study proposed a two-step optically-induced dielectrophoresis (ODEP) cell manipulation to process the cell sample harvested by negative selection-/immunomagnetic microbeads-based CTC isolation. The working mechanism is that the ODEP force acting on the cells with and without magnetic microbeads binding is different. Accordingly, the use of ODEP cell manipulation in a microfluidic system was designed to first separate and then isolate the cancer cells from other magnetic microbead-bound cells. Immunofluorescent microscopic observation and ODEP cell manipulation were then performed to refine the purity of the cancer cells. In this study, the optimum operating conditions for effective cell isolation were determined experimentally. The results revealed that the presented method was able to further refine the purity of cancer cell in the sample obtained after negative selection-based CTC isolation with high cell purity (81.6~86.1%). Overall, this study proposed the combination of immunomagnetic bead-based cell isolation and ODEP cell manipulation for the negative selection-based isolation of CTCs.

New Screening Test Improves Detection of Prostate Cancer Using Circulating Tumor Cells and Prostate-Specific Markers.

The current screening-test for prostate cancer, affecting 10% of men worldwide, has a high false negative rate and a low true positive rate. A more reliable screening test is needed. Circulating-Tumor-Cells (CTC) provide a biomarker for early carcinogenesis, cancer progression and treatment effectiveness. The cytology-based ISET®-CTC Test is a clinically validated blood test with high sensitivity and specificity. This study aimed to evaluate the ISET®-CTC test combined with prostate-specific-marker staining as a screening test for the detection of prostate cancer. We selected a group of 47 men from our ongoing CTC screening study involving 2,000 patient-tests from Sep-2014 to July-2019, who also underwent standard diagnostic cancer testing before or after CTC testing. While 20 of the 47 men were diagnosed with prostate cancer before the ISET®-CTC test, 27 men underwent screening. We studied the CTC identified in 45 CTC-positive men by Immuno-Cyto-Chemistry (ICC) assays with the prostate-specific-marker PSA. CTC were ICC-PSA-marker positive in all men diagnosed with primary prostate cancer (n = 20). Secondary cancers were detected in 63% (n = 7/11) of men with mixed CTC-population (ICC-PSA-positive/ICC-PSA-negative). Of the 27 men screened, 25 had CTC, and 84% of those (n = 20) were positive for the prostate-specific-PSA-marker. Follow-up testing suggested suspected prostate cancer in 20/20 men by a positive PSMA-PET scan, and biopsies performed in 45% (n = 9/20) men confirmed the diagnosis of early prostate cancer. Kidney cancer or B-cell lymphoma were detected in two men with ICC-PSA-marker negative CTC. Our study suggests that the combination of ISET®-CTC and ICC-PSA-marker-testing has an estimated positive-predictive-value (PPV) of 99% and a negative-predictive-value (NPV) of 97%, providing a more reliable screening test for prostate cancer than the standard PSA-blood-test (PPV = 25%; NPV = 15.5%). Our findings warrant further studies to evaluate the new test's potential for prostate cancer screening on a population level.

Insulin-like growth factor-1 receptor (IGF-1R) expression on circulating tumor cells (CTCs) and metastatic breast cancer outcome: results from the TransMYME trial.

To evaluate the prognostic value of IGF-1R expression on circulating tumor cells (CTCs) in a prospective randomized clinical trial comparing chemotherapy plus metformin with chemotherapy alone in metastatic breast cancer (MBC) patients. CTCs were collected at baseline and at the end of chemotherapy. An automated sample preparation and analysis system (CellSearch) were customized for detecting IGF-1R expression. The prognostic role of CTC count and IGF-1R was assessed for PFS and OS by univariate and multivariate analyses. Seventy-two out of 126 randomized patients were evaluated: 57% had ≥ 1 IGF-1R positive CTC and 37.5% ≥ 4 IGF-1R negative cells; 42% had CTC count ≥ 5/7.5ml. At univariate analysis, the number of IGF-1R negative CTCs was strongly associated with risk of progression and death: HR 1.93 (P = 0.013) and 3.65 (P = 0.001), respectively; no association was detected between number of IGF-1R positive CTCs and PFS or OS (P = 0.322 and P = 0.840). The prognostic role of CTC count was confirmed: HR 1.69, P = 0.042 for PFS and HR 2.80 for OS, P = 0.002. By multivariate analysis, the prognostic role of the number of IGF-1R negative CTCs was maintained, while no residual prognostic role of CTC count or number of IGF-1R positive cells was found. Loss of IGF-1R in CTCs is associated with a significantly worse outcome in MBC patients. This finding supports further evaluation for the role of IGF-1R on CTCs to improve patient stratification and to implement new targeted strategies. Clinicaltrials.gov (NCT01885013); European Clinical Trials Database (EudraCT No.2009-014,662-26).