SUMMARY Clusters of circulating tumor cells (CTC-clusters) are present in the blood of patients with cancer but their contribution to metastasis is not well defined. Using mouse models with tagged mammary tumors, we demonstrate that CTC-clusters arise from oligoclonal tumor cell groupings and not from intravascular aggregation events. Although rare in the circulation compared with single CTCs, CTC-clusters have 23-50-fold increased metastatic potential. In patients with breast cancer, single-cell resolution RNA sequencing of CTC-clusters and single CTCs, matched within individual blood samples, identifies the cell junction component plakoglobin as highly differentially expressed. In mouse models, knockdown of plakoglobin abrogates CTC-cluster formation and suppresses lung metastases. In breast cancer patients, both abundance of CTC-clusters and high tumor plakoglobin levels denote adverse outcomes. Thus, CTC-clusters are derived from multicellular groupings of primary tumor cells held together through plakoglobin-dependent intercellular adhesion, and while rare, they greatly contribute to the metastatic spread of cancer.

Epithelial-mesenchymal transition (EMT) of adherent epithelial cells to a migratory mesenchymal state has been implicated in tumor metastasis in preclinical models. To investigate its role in human cancer, we characterized EMT in circulating tumor cells (CTCs) from breast cancer patients. Rare primary tumor cells simultaneously expressed mesenchymal and epithelial markers, but mesenchymal cells were highly enriched in CTCs. Serial CTC monitoring in 11 patients suggested an association of mesenchymal CTCs with disease progression. In an index patient, reversible shifts between these cell fates accompanied each cycle of response to therapy and disease progression. Mesenchymal CTCs occurred as both single cells and multicellular clusters, expressing known EMT regulators, including transforming growth factor (TGF)–β pathway components and the FOXC1 transcription factor. These data support a role for EMT in the blood-borne dissemination of human breast cancer.

Circulating tumor cells (CTCs) are present at low concentrations in the peripheral blood of patients with solid tumors. It has been proposed that the isolation, ex vivo culture, and characterization of CTCs may provide an opportunity to noninvasively monitor the changing patterns of drug susceptibility in individual patients as their tumors acquire new mutations. In a proof-of-concept study, we established CTC cultures from six patients with estrogen receptor–positive breast cancer. Three of five CTC lines tested were tumorigenic in mice. Genome sequencing of the CTC lines revealed preexisting mutations in the PIK3CA gene and newly acquired mutations in the estrogen receptor gene (ESR1), PIK3CA gene, and fibroblast growth factor receptor gene (FGFR2), among others. Drug sensitivity testing of CTC lines with multiple mutations revealed potential new therapeutic targets. With optimization of CTC culture conditions, this strategy may help identify the best therapies for individual cancer patients over the course of their disease.

Circulating tumor cells (CTCs) are shed into the bloodstream from primary and metastatic tumor deposits. Their isolation and analysis hold great promise for the early detection of invasive cancer and the management of advanced disease, but technological hurdles have limited their broad clinical utility. We describe an inertial focusing–enhanced microfluidic CTC capture platform, termed “CTC-iChip,” that is capable of sorting rare CTCs from whole blood at 107 cells/s. Most importantly, the iChip is capable of isolating CTCs using strategies that are either dependent or independent of tumor membrane epitopes, and thus applicable to virtually all cancers. We specifically demonstrate the use of the iChip in an expanded set of both epithelial and nonepithelial cancers including lung, prostate, pancreas, breast, and melanoma. The sorting of CTCs as unfixed cells in solution allows for the application of high-quality clinically standardized morphological and immunohistochemical analyses, as well as RNA-based single-cell molecular characterization. The combination of an unbiased, broadly applicable, high-throughput, and automatable rare cell sorting technology with generally accepted molecular assays and cytology standards will enable the integration of CTC-based diagnostics into the clinical management of cancer.

Prostate cancer is initially responsive to androgen deprivation, but the effectiveness of androgen receptor (AR) inhibitors in recurrent disease is variable. Biopsy of bone metastases is challenging, hence sampling circulating tumor cells (CTCs) may reveal drug resistance mechanisms. We established single cell RNA-sequencing profiles of 77 intact CTCs isolated from 13 patients (mean 6 CTCs/patient) using microfluidic enrichment. Single CTCs from each individual display considerable heterogeneity, including expression of AR gene mutations and splicing variants. Retrospective analysis of CTCs from patients progressing on AR inhibitor, compared with untreated cases indicates activation of noncanonical Wnt signaling (P=0.0064). Ectopic expression of Wnt5a in prostate cancer cells attenuates the antiproliferative effect of AR inhibition, while its suppression in drug-resistant cells restores partial sensitivity, a correlation also evident in an established mouse model. Thus, single cell analysis of prostate CTCs reveals heterogeneity in signaling pathways that could contribute to treatment failure.

Cancer cells metastasize through the bloodstream either as single migratory circulating tumor cells (CTCs) or as multicellular groupings (CTC-clusters). Existing technologies for CTC enrichment are designed primarily to isolate single CTCs, and while CTC-clusters are detectable in some cases, their true prevalence and significance remain to be determined. Here, we developed a microchip technology (Cluster-Chip) specifically designed to capture CTC-clusters independent of tumor-specific markers from unprocessed blood. CTC-clusters are isolated through specialized bifurcating traps under low shear-stress conditions that preserve their integrity and even two-cell clusters are captured efficiently. Using the Cluster-Chip, we identify CTC-clusters in 30–40% of patients with metastatic cancers of the breast, prostate and melanoma. RNA sequencing of CTC-clusters confirms their tumor origin and identifies leukocytes within the clusters as tissue-derived macrophages. Together, the development of a device for efficient capture of CTC-clusters will enable detailed characterization of their biological properties and role in cancer metastasis.

Summary The aberrant transcription factor EWS-FLI1 drives Ewing sarcoma yet its molecular function is incompletely understood. We find that EWS-FLI1 reprograms gene regulatory circuits in Ewing sarcoma by directly inducing or repressing enhancers. At GGAA repeat elements, which lack evolutionary conservation and regulatory potential in other cell types, EWS-FLI1 multimers induce chromatin opening and create de novo enhancers that physically interact with target promoters. Conversely, EWS-FLI1 inactivates conserved enhancers containing canonical ETS motifs by displacing wild type ETS transcription factors. These divergent chromatin-remodeling patterns repress tumor suppressors and mesenchymal lineage regulators, while activating oncogenes and new potential therapeutic targets, such as the kinase VRK1. Our findings demonstrate how EWS-FLI1 establishes an oncogenic regulatory program governing both tumor survival and differentiation.

Purpose On the basis of the ACCORD trial, FOLFIRINOX is effective in metastatic pancreatic adenocarcinoma (PDAC), making it a rational choice for locally advanced PDAC (LA). Aims of this study are to evaluate the accuracy of imaging in determining the resectability of PDAC and to determine the surgical and clinicopathologic outcomes of pancreatic resections after neoadjuvant FOLFIRINOX therapy. Patients and Methods Clinicopathologic data were retrospectively collected for surgical PDAC patients receiving neoadjuvant FOLFIRINOX or no neoadjuvant therapy between April 2011 and February 2014. Americas Hepato-Pancreato-Biliary Association/Society of Surgical Oncology/Society for Surgery of the Alimentary Tract consensus guidelines defined LA and borderline. Imaging was reviewed by a blinded senior pancreatic surgeon. Results Of 188 patients undergoing resection for PDAC, 40 LA/borderline received FOLFIRINOX and 87 received no neoadjuvant therapy. FOLFIRINOX resulted in a significant decrease in tumor size, yet 19 patients were still classified as LA and 9 as borderline. Despite post-FOLFIRINOX imaging suggesting continued unresectability, 92% had an R0 resection. When compared with no neoadjuvant therapy, FOLFIRINOX resulted in significantly longer operative times (393 vs 300 minutes) and blood loss (600 vs 400 mL), but significantly lower operative morbidity (36% vs 63%) and no postoperative pancreatic fistulas. Length of stay (6 vs 7 days), readmissions (20% vs 30%), and mortality were equivalent (1% vs 0%). On final pathology, the FOLFIRINOX group had a significant decrease in lymph node positivity (35% vs 79%) and perineural invasion (72% vs 95%). Median follow-up was 11 months with a significant increase in overall survival with FOLFIRINOX. Conclusions After neoadjuvant FOLFIRINOX imaging no longer predicts unresectability. Traditional pathologic predictors of survival are improved, and morbidity is decreased in comparison to patients with clearly resectable cancers at the time of presentation.