Introduction: Epithelial to mesenchymal transition (EMT) is considered an essential process in the metastatic cascade. EMT is characterised by upregulation of vimentin, Twist, Snail, Slug and Sip1 among others. Metastasis is also associated with the presence of circulating tumour cells (CTCs) and disseminated tumour cells in the blood and bone marrow, respectively, of breast cancer patients, but the expression of EMT markers in these cells has not been reported so far. Methods: The expression of Twist and vimentin in CTCs of 25 metastatic and 25 early breast cancer patients was investigated by using double-immunofluorescence experiments in isolated peripheral blood mononuclear cell cytospins using anti-cytokeratin (anti-CK) anti-mouse (A45-B/B3) and anti-Twist or anti-vimentin anti-rabbit antibodies. Results: Among early breast cancer patients, vimentin-and Twist-expressing CK⁺ CTCs were identified in 77% and 73% of the patients, respectively, and in 100% of the patients with metastatic breast cancer for both markers (P = 0.004 and P = 0.037, respectively). Among patients with early disease, 56% and 53% of the CK⁺ CTCs were double-stained with vimentin and Twist, and the corresponding values for metastatic patients were 74% and 97%, respectively (P = 0.005 and P = 0.0001, respectively). The median expression of CK⁺vimentin⁺ and CK⁺Twist⁺ cells per patient in metastatic patients was 98% and 100%, and in an adjuvant chemotherapy setting the corresponding numbers were 56% and 40.6%, respectively. Triple-staining experiments revealed that all CK⁺Twist⁺ or CK⁺vimentin⁺ cells were also CD45^-, confirming their epithelial origin. Immunomagnetic separation of CTCs and triple-immunofluorescence with anti-CK/anti-Twist/anti-vimentin antibodies demonstrated that both mesenchymal markers could be coexpressed in the same CK⁺ cell, since 64% of the total identified CTCs were triple-stained. There was a significant correlation (P = 0.005) between the number of CTCs expressing Twist and vimentin within the same setting. Conclusions: CTCs expressing Twist and vimentin, suggestive of EMT, are identified in patients with breast cancer. The high incidence of these cells in patients with metastatic disease compared to early stage breast cancer strongly supports the notion that EMT is involved in the metastatic potential of CTCs.

The detection of circulating tumor cells (CTCs) in peripheral blood (PB) of patients with breast cancer predicts poor clinical outcome. Cancer cells with stemness and epithelial-to-mesenchymal transition (EMT) features display enhanced malignant and metastatic potential. A new methodology was developed in order to investigate the co-expression of a stemness and an EMT marker (ALDH1 and TWIST, respectively) on single CTCs of patients with early and metastatic breast cancer. Triple immunofluorescence using anti-pancytokeratin (A45-B/B3), anti-ALDH1 and anti-TWIST antibodies was performed in cytospins prepared from hepatocellular carcinoma HepG2 cells and SKBR-3, MCF-7 and MDA.MB.231 breast cancer cell lines. Evaluation of ALDH1 expression levels (high, low or absent) and TWIST subcellular localization (nuclear, cytoplasmic or absent) was performed using the ARIOL system. Cytospins prepared from peripheral blood of patients with early (n = 80) and metastatic (n = 50) breast cancer were analyzed for CTC detection (based on pan-cytokeratin expression and cytomorphological criteria) and characterized according to ALDH1 and TWIST. CTCs were detected in 13 (16%) and 25 (50%) patients with early and metastatic disease, respectively. High ALDH1 expression (ALDH1high) and nuclear TWIST localization (TWISTnuc) on CTCs was confirmed in more patients with metastatic than early breast cancer (80% vs. 30.8%, respectively; p = 0.009). In early disease, ALDH1low/neg CTCs (p = 0.006) and TWISTcyt/neg CTCs (p = 0.040) were mainly observed. Regarding co-expression of these markers, ALDH1high/TWISTnuc CTCs were more frequently evident in the metastatic setting (76% vs. 15.4% of patients, p = 0.001; 61.5% vs. 12.9% of total CTCs), whereas in early disease ALDH1low/neg/TWISTcyt/neg CTCs were mainly detected (61.5% vs. 20% of patients, p = 0.078; 41.9% vs. 7.7% of total CTCs). A new assay is provided for the evaluation of ALDH1 and TWIST co-expression at the single CTC-level in patients with breast cancer. A differential expression pattern for these markers was observed both in early and metastatic disease. CTCs expressing high ALDH1, along with nuclear TWIST were more frequently detected in patients with metastatic breast cancer, suggesting that these cells may prevail during disease progression.

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

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

The truncated form of human epidermal growth factor receptor 2 (p95HER2) lacks the HER2 extracellular domain and has been associated with poor prognosis and resistance to trastuzumab. In the present study, the expression of p95HER2 was investigated on circulating tumor cells (CTCs) from breast cancer patients. Triple-staining immunofluorescent experiments were performed on peripheral blood mononuclear cells’ (PBMCs) cytospins obtained from patients with early (n = 24) and metastatic (n = 37) breast cancer. Cells were stained with the pancytokeratin (A45-B/B3) antibody coupled with antibodies against the extracellular (ECD) and the intracellular (ICD) domains of HER2. Slides were analyzed with either confocal laser scanning microscopy or with the Ariol system. HER2-positive CTCs were identified in 55.6 % of early and 65.2 % of metastatic CTC-positive breast cancer patients. p95HER2-positive CTCs were identified in 11.1 % of early and 39.1 % of metastatic breast cancer patients (p = 0.047). In 14 patients with metastatic HER2-positive breast cancer, CTCs were also analyzed before and after first-line trastuzumab therapy. Trastuzumab reduced the percentage of patients with full-length HER2-positive CTCs from 70 % at baseline to 50 % (p = 0.035) after treatment while increased the percentage of patients with p95HER2-positive CTCs from 40 % to 63 %. Moreover, the overall survival of metastatic patients with p95HER2-positive CTCs was significantly decreased (p = 0.03). p95HER2-positive CTCs can be detected in both early and metastatic breast cancer patients. Their incidence is increased in the metastatic setting and their presence is associated with poor survival. Longitudinal studies during anti-HER2 treatment are required to determine the clinical relevance of p95HER2-expressing CTCs.

KRAS mutations are found in approximately one third of non-small cell lung cancer (NSCLC) patients. In this study, we aim to investigate whether KRAS G12/G13 mutant allele fraction (MAF) in cell-free DNA (cfDNA) can provide meaningful prognostic information in NSCLC. Multiplex droplet-digital PCR was used to quantitatively assess KRAS G12/G13 MAF in cfDNA from 114 pre-treated advanced disease NSCLC patients. In 14 patients, changes in KRAS G12/G13 MAF were longitudinally monitored during treatment. Plasma KRAS G12/G13 status was associated with poor patients’ outcome in terms of progression-free survival (PFS) (p < 0.001) and overall survival (OS) (p < 0.001). In multivariate analysis, the detection of plasma KRAS mutations was an independent predictor of adverse PFS (HR = 3.12; p < 0.001) and OS (HR = 2.53; p = 0.002). KRAS G12/G13 MAF at first treatment evaluation (T1) was higher (p = 0.013) among patients experiencing progressive disease compared to those with disease control, and increased KRAS MAF at T1 was associated (p = 0.005) with shorter PFS. On the contrary, no association was observed between tissue KRAS mutation status and patients’ prognosis. Our results show that ddPCR-based detection of KRAS G12/G13 mutations in plasma could serve as an independent biomarker of unfavorable prognosis in NSCLC patients. Changes in KRAS MAF can provide valuable information for monitoring patient outcome during treatment.