A better understanding of the features that define the interplay between cancer cells and immune cells is key to identify new cancer therapies 1 . Yet, focus is often given to those interactions that occur within the primary tumor and its microenvironment, while the role of immune cells during cancer dissemination in patients remains largely uncharacterized 2,3 . Circulating tumor cells (CTCs) are precursors of metastasis in several cancer types [4][5][6] , and are occasionally found within the bloodstream in association with non-malignant cells such as white blood cells (WBCs) 7,8 . The identity and function of these CTC-associated WBCs, as well as the molecular features that define the interaction between WBCs and CTCs are unknown. Here, we achieve the isolation and interrogation of individual CTC-associated WBCs, alongside with corresponding cancer cells within each CTC-WBC cluster, from multiple breast cancer patients and mouse models. Single-cell RNA sequencing reveals a specific pattern of WBCs attached to CTCs, with neutrophils representing the majority of the cases. When comparing the transcriptome profiles of CTCs that were associated to neutrophils with that of CTCs alone, we detect a number of differentially expressed genes that outline cell cycle progression, leading to a higher ability to efficiently seed metastasis. Additionally, we identify cell-cell junction and cytokine-receptor pairs that define CTC-neutrophil clusters, representing key vulnerabilities of the metastatic process. Thus, the association between neutrophils and CTCs fuels cell cycle progression within the bloodstream and expands the metastatic potential of CTCs, providing a rationale for targeting this interaction in breast cancer. 3/28 Main TextCirculating tumor cells (CTCs) are precursors of metastasis in various solid cancers including breast cancer 6 , and are occasionally found in association to white blood cells (WBCs) 7 . The role of CTC-WBC clusters in metastasis development as well as the principles that govern the interplay between CTCs and WBCs during blood-borne metastasis are largely uncharacterized.We first sought to determine the number and composition of CTC-WBC clusters in breast cancer patients and mouse models. We obtained blood samples from 70 patients with invasive breast cancer that discontinued their treatment due to progressive disease, as well as from five different breast cancer mouse models, and we enriched for CTCs using the Parsortix microfluidic device 9 (Extended Data Fig. 1a-e). Live CTCs were stained for cancer-associated cell surface markers EpCAM, HER2, and EGFR or imaged directly for the expression of GFP, as well as labeled for CD45 to identify WBCs (Fig. 1a and Extended Data Fig. 1f). Among 70 patients, 34 (48.6%) had detectable CTCs, with a mean number of 22 CTCs per 7.5ml of blood (Supplementary Tables 1 and 2). While the majority of CTCs were single (88.0%), we also detected CTC clusters (8.6%) and CTC-WBC clusters (3.4%) (Fig. 1b and Extended Data Fig. 1g,h). Similarly, we observed that CTC-...

SummaryThe ability of circulating tumor cells (CTCs) to form clusters has been linked to increased metastatic potential. Yet biological features and vulnerabilities of CTC clusters remain largely unknown. Here, we profile the DNA methylation landscape of single CTCs and CTC clusters from breast cancer patients and mouse models on a genome-wide scale. We find that binding sites for stemness- and proliferation-associated transcription factors are specifically hypomethylated in CTC clusters, including binding sites for OCT4, NANOG, SOX2, and SIN3A, paralleling embryonic stem cell biology. Among 2,486 FDA-approved compounds, we identify Na+/K+ ATPase inhibitors that enable the dissociation of CTC clusters into single cells, leading to DNA methylation remodeling at critical sites and metastasis suppression. Thus, our results link CTC clustering to specific changes in DNA methylation that promote stemness and metastasis and point to cluster-targeting compounds to suppress the spread of cancer.

This study documents the long-term outcome of [(90)Y-DOTA]-TOC treatment in a large cohort. Response to [(90)Y-DOTA]-TOC is associated with longer survival. Somatostatin receptor imaging is predictive for both survival after [(90)Y-DOTA]-TOC treatment and occurrence of renal toxicity.

BackgroundInsulin-like growth factor-1 (IGF-I) signalling is important for cancer initiation and progression. Given the emerging evidence for the role of the stroma in these processes, we aimed to characterize the effects of IGF-I on cancer cells and stromal cells separately.MethodsWe used an ex vivo culture model and measured gene expression changes after IGF-I stimulation with cDNA microarrays. In vitro data were correlated with in vivo findings by comparing the results with published expression datasets on human cancer biopsies.ResultsUpon stimulation with IGF-I, breast cancer cells and stromal fibroblasts show some common and other distinct response patterns. Among the up-regulated genes in the stromal fibroblasts we observed a significant enrichment in proliferation associated genes. The expression of the IGF-I induced genes was coherent and it provided a basis for the segregation of the patients into two groups. Patients with tumours with highly expressed IGF-I induced genes had a significantly lower survival rate than patients whose tumours showed lower levels of IGF-I induced gene expression (P = 0.029 - Norway/Stanford and P = 7.96e-09 - NKI dataset). Furthermore, based on an IGF-I induced gene expression signature derived from primary lung fibroblasts, a separation of prognostically different lung cancers was possible (P = 0.007 - Bhattacharjee and P = 0.008 - Garber dataset).ConclusionExpression patterns of genes induced by IGF-I in primary breast and lung fibroblasts accurately predict outcomes in breast and lung cancer patients. Furthermore, these IGF-I induced gene signatures derived from stromal fibroblasts might be promising predictors for the response to IGF-I targeted therapies.See the related commentary by Werner and Bruchim: http://www.biomedcentral.com/1741-7015/8/2