A reinforcement learning framework for pooled oligonucleotide design.

MOTIVATION: The goal of oligonucleotide (oligo) design is to select oligos that optimize a set of design criteria. Oligo design problems are combinatorial in nature and require computationally intensive models to evaluate design criteria. Even relatively small problems can be intractable for brute-force approaches that test every possible combination of oligos, so heuristic approaches must be used to find near-optimal solutions. RESULTS: We present a general reinforcement learning (RL) framework, called OligoRL, to solve oligo design problems with complex constraints. OligoRL allows 'black-box' design criteria and can be adapted to solve many oligo design problems. We highlight the flexibility of OligoRL by building tools to solve three distinct design problems: (i) finding pools of random DNA barcodes that lack restriction enzyme recognition sequences (CutFreeRL); (ii) compressing large, non-degenerate oligo pools into smaller degenerate ones (OligoCompressor) and (iii) finding Not-So-Random hexamer primer pools that avoid rRNA and other unwanted transcripts during RNA-seq library preparation (NSR-RL). OligoRL demonstrates how RL offers a general solution for complex oligo design problems. AVAILABILITY AND IMPLEMENTATION: OligoRL and all simulation codes are available as a Julia package at http://jensenlab.net/tools and archived at https://archive.softwareheritage.org/browse/origin/directory/?origin_url=https://github.com/bmdavid2/OligoRL. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Nucleus of Circulating Tumor Cell Determines Its Translocation Through Biomimetic Microconstrictions and Its Physical Enrichment by Microfiltration.

The mechanism of cells passing through microconstrictions, such as capillaries and endothelial junctions, influences metastasis of circulating tumor cells (CTCs) in vivo, as well as size-based enrichment of CTCs in vitro. However, very few studies observe such translocation of microconstrictions in real time, and thus the inherent biophysical mechanism is poorly understood. In this study, a multiplexed microfluidic device is fabricated for real-time tracking of cell translocation under physiological pressure and recording deformation of the whole cell and nucleus, respectively. It is found that the deformability and size of the nucleus instead of the whole cell dominate cellular translocation through microconstrictions under a normal physiological pressure range. More specifically, cells with a large and stiff nucleus are prone to be blocked by relatively small constrictions. The same phenomenon is also observed in the size-based enrichment of CTCs from peripheral blood of metastatic cancer patients. These findings are different from a popular viewpoint that the size and deformability of a whole cell mainly determine cell translation through microconstrictions, and thus may elucidate interactions between CTCs and capillaries from a new perspective and guide the rational design of size-based microfilters for rare cell enrichment.

Flexible micro spring array device for high-throughput enrichment of viable circulating tumor cells.

BACKGROUND: The dissemination of circulating tumor cells (CTCs) that cause metastases in distant organs accounts for the majority of cancer-related deaths. CTCs have been established as a cancer biomarker of known prognostic value. The enrichment of viable CTCs for ex vivo analysis could further improve cancer diagnosis and guide treatment selection. We designed a new flexible micro spring array (FMSA) device for the enrichment of viable CTCs independent of antigen expression. METHODS: Unlike previous microfiltration devices, flexible structures at the micro scale minimize cell damage to preserve viability, while maximizing throughput to allow rapid enrichment directly from whole blood with no need for sample preprocessing. Device performance with respect to capture efficiency, enrichment against leukocytes, viability, and proliferability was characterized. CTCs and CTC microclusters were enriched from clinical samples obtained from breast, lung, and colorectal cancer patients. RESULTS: The FMSA device enriched tumor cells with 90% capture efficiency, higher than 10(4) enrichment, and better than 80% viability from 7.5-mL whole blood samples in <10 min on a 0.5-cm(2) device. The FMSA detected at least 1 CTC in 16 out of 21 clinical samples (approximately 76%) compared to 4 out of 18 (approximately 22%) detected with the commercial CellSearch® system. There was no incidence of clogging in over 100 tested fresh whole blood samples. CONCLUSIONS: The FMSA device provides a versatile platform capable of viable enrichment and analysis of CTCs from clinically relevant volumes of whole blood.

A Dual-Filtration System for Single-Cell Sequencing of Circulating Tumor Cells and Clusters in HCC.

Hepatocellular carcinoma (HCC) is a leading cause of cancer death worldwide. Identification and sequencing of circulating tumor (CT) cells and clusters may allow for noninvasive molecular characterization of HCC, which is an unmet need, as many patients with HCC do not undergo biopsy. We evaluated CT cells and clusters, collected using a dual-filtration system in patients with HCC. We collected and filtered whole blood from patients with HCC and selected individual CT cells and clusters with a micropipette. Reverse transcription, polymerase chain reaction, and library preparation were performed using a SmartSeq2 protocol, followed by single-cell RNA sequencing (scRNAseq) on an Illumina MiSeq V3 platform. Of the 8 patients recruited, 6 had identifiable CT cells or clusters. Median age was 64 years old; 7 of 8 were male; and 7 of 8 had and Barcelona Clinic Liver Cancer stage C. We performed scRNAseq of 38 CT cells and 33 clusters from these patients. These CT cells and clusters formed two distinct groups. Group 1 had significantly higher expression than group 2 of markers associated with epithelial phenotypes (CDH1 [Cadherin 1], EPCAM [epithelial cell adhesion molecule], ASGR2 [asialoglycoprotein receptor 2], and KRT8 [Keratin 8]), epithelial-mesenchymal transition (VIM [Vimentin]), and stemness (PROM1 [CD133], POU5F1 [POU domain, class 5, transcription factor 1], NOTCH1, STAT3 [signal transducer and activator of transcription 3]) (P < 0.05 for all). Patients with identifiable group 1 cells or clusters had poorer prognosis than those without them (median overall survival 39 vs. 384 days; P = 0.048 by log-rank test). Conclusion: A simple dual-filtration system allows for isolation and sequencing of CT cells and clusters in HCC and may identify cells expressing candidate genes known to be involved in cancer biology. Presence of CT cells/clusters expressing candidate genes is associated with poorer prognosis in advanced-stage HCC.

Expansion of Circulating Tumor Cells from Patients with Locally Advanced Pancreatic Cancer Enable Patient Derived Xenografts and Functional Studies for Personalized Medicine.

Improvement in pancreatic cancer treatment represents an urgent medical goal that has been hampered by the lack of predictive biomarkers. Circulating Tumor Cells (CTCs) may be able to overcome this issue by allowing the monitoring of therapeutic response and tumor aggressiveness through ex vivo expansion. The successful expansion of CTCs is challenging, due to their low numbers in blood and the high abundance of blood cells. Here, we explored the utility of pancreatic CTC cultures as a preclinical model for treatment response. CTCs were isolated from ten patients with locally advanced pancreatic cancer using the Labyrinth, a biomarker independent, size based, inertial microfluidic separation device. Three patient-derived CTC samples were successfully expanded in adherent and spheroid cultures. Molecular and functional characterization was performed on the expanded CTC lines. CTC lines exhibited KRAS mutations, consistent with pancreatic cancers. Additionally, we evaluated take rate and metastatic potential in vivo and examined the utility of CTC lines for cytotoxicity assays. Patient derived expanded CTCs successfully generated patient derived xenograft (PDX) models with a 100% take rate. Our results demonstrate that CTC cultures are possible and provide a valuable resource for translational pancreatic cancer research, while also providing meaningful insight into the development of distant metastasis, as well as treatment resistance.

High-Throughput Label-Free Isolation of Heterogeneous Circulating Tumor Cells and CTC Clusters from Non-Small-Cell Lung Cancer Patients.

(1) Background: Circulating tumor cell (CTC) clusters are emerging as clinically significant harbingers of metastases in solid organ cancers. Prior to engaging these CTC clusters in animal models of metastases, it is imperative for technology to identify them with high sensitivity. These clusters often present heterogeneous surface markers and current methods for isolation of clusters may fall short. (2) Methods: We applied an inertial microfluidic Labyrinth device for high-throughput, biomarker-independent, size-based isolation of CTCs/CTC clusters from patients with metastatic non-small-cell lung cancer (NSCLC). (3) Results: Using Labyrinth, CTCs (PanCK+/DAPI+/CD45-) were isolated from patients (n = 25). Heterogeneous CTC populations, including CTCs expressing epithelial (EpCAM), mesenchymal (Vimentin) or both markers were detected. CTCs were isolated from 100% of patients (417 ± 1023 CTCs/mL). EpCAM- CTCs were significantly greater than EpCAM+ CTCs. Cell clusters of ≥2 CTCs were observed in 96% of patients-of which, 75% were EpCAM-. CTCs revealed identical genetic aberrations as the primary tumor for RET, ROS1, and ALK genes using fluorescence in situ hybridization (FISH) analysis. (4) Conclusions: The Labyrinth device recovered heterogeneous CTCs in 100% and CTC clusters in 96% of patients with metastatic NSCLC. The majority of recovered CTCs/clusters were EpCAM-, suggesting that these would have been missed using traditional antibody-based capture methods.

Targeting LRP8 inhibits breast cancer stem cells in triple-negative breast cancer.

Triple-negative breast cancer (TNBC) is the most difficult subtype of breast cancer to treat due to a paucity of effective targeted therapies. Many studies have reported that breast cancer stem cells (BCSCs) are enriched in TNBC and are responsible for chemoresistance and metastasis. In this study, we identify LRP8 as a novel positive regulator of BCSCs in TNBC. LRP8 is highly expressed in TNBC compared to other breast cancer subtypes and its genomic locus is amplified in 24% of TNBC tumors. Knockdown of LRP8 in TNBC cell lines inhibits Wnt/ß-catenin signaling, decreases BCSCs, and suppresses tumorigenic potential in xenograft models. LRP8 knockdown also induces a more differentiated, luminal-epithelial phenotype and thus sensitizes the TNBC cells to chemotherapy. Together, our study highlights LRP8 as a novel therapeutic target for TNBC as inhibition of LRP8 can attenuate Wnt/ß-catenin signaling to suppress BCSCs.

Heterogeneity of Human Breast Stem and Progenitor Cells as Revealed by Transcriptional Profiling.

During development, the mammary gland undergoes extensive remodeling driven by stem cells. Breast cancers are also hierarchically organized and driven by cancer stem cells characterized by CD44+CD24low/- or aldehyde dehydrogenase (ALDH) expression. These markers identify mesenchymal and epithelial populations both capable of tumor initiation. Less is known about these populations in non-cancerous mammary glands. From RNA sequencing, ALDH+ and ALDH-CD44+CD24- human mammary cells have epithelial-like and mesenchymal-like characteristics, respectively, with some co-expressing ALDH+ and CD44+CD24- by flow cytometry. At the single-cell level, these cells have the greatest mammosphere-forming capacity and express high levels of stemness and epithelial-to-mesenchymal transition-associated genes including ID1, SOX2, TWIST1, and ZEB2. We further identify single ALDH+ cells with a hybrid epithelial/mesenchymal phenotype that express genes associated with aggressive triple-negative breast cancers. These results highlight single-cell analyses to characterize tissue heterogeneity, even in marker-enriched populations, and identify genes and pathways that define this heterogeneity.

Targeting Breast Cancer Stem Cell State Equilibrium through Modulation of Redox Signaling.

Although breast cancer stem cells (BCSCs) display plasticity transitioning between quiescent mesenchymal-like (M) and proliferative epithelial-like (E) states, how this plasticity is regulated by metabolic or oxidative stress remains poorly understood. Here, we show that M- and E-BCSCs rely on distinct metabolic pathways and display markedly different sensitivities to inhibitors of glycolysis and redox metabolism. Metabolic or oxidative stress generated by 2DG, H2O2, or hypoxia promotes the transition of ROSlo M-BCSCs to a ROShi E-state. This transition is reversed by N-acetylcysteine and mediated by activation of the AMPK-HIF1α axis. Moreover, E-BCSCs exhibit robust NRF2-mediated antioxidant responses, rendering them vulnerable to ROS-induced differentiation and cytotoxicity following suppression of NRF2 or downstream thioredoxin (TXN) and glutathione (GSH) antioxidant pathways. Co-inhibition of glycolysis and TXN and GSH pathways suppresses tumor growth, tumor-initiating potential, and metastasis by eliminating both M- and E-BCSCs. Exploiting metabolic vulnerabilities of distinct BCSC states provides a novel therapeutic approach targeting this critical tumor cell population.

Evaluating a novel dimensional reduction approach for mechanical fractionation of cells using a tandem flexible micro spring array (tFMSA).

We present a novel methodology to establish experimental models for the rational design of cell fractionation based on physical properties of cells. Label-free microfluidic separation of cells based on size is a widely employed technique. However, close observation reveals that cell capture results cannot be explained by cell sizes alone. This is particularly apparent with viable cell fractionation, where cells retain their native deformability. We have developed a principal size cutoff (PSC) model based on the analysis of size distribution and size-based filtration efficiency for cell populations. The goal of this analysis is to use an unbiased approach to achieve dimensional reduction of deformability and other mechanical properties that affect cell capture. The PSC model provides a single calibrated principal size component that may be compared directly to device gap width, which is the critical dimension for cell filtration. The PSC model was evaluated experimentally using a tandem flexible micro spring array (tFMSA) device made of parylene filtration elements applied within micro-molded polydimethylsiloxane (PDMS) chambers. In the tFMSA device, a mixture of cells is sequentially passed through individual filters with decreasing gap widths to allow size-based selection. We applied this method to demonstrate viable separation of subgroups of cells with different mechanical properties from complex mixtures, including fractionation according to cancer cell type, cell cycle stage, cell viability status, and leukocyte nuclear phenotype. The PSC methodology and tFMSA device can advance a better understanding of complex factors affecting mechanical cell fractionation and provide a miniature platform for obtaining rationally designed cell fractions for biomedical applications.

RAD51 Mediates Resistance of Cancer Stem Cells to PARP Inhibition in Triple-Negative Breast Cancer.

INTRODUCTION: PARP inhibitors have shown promising results in early studies for treatment of breast cancer susceptibility gene (BRCA)-deficient breast cancers; however, resistance ultimately develops. Furthermore, the benefit of PARP inhibitors (PARPi) in triple-negative breast cancers (TNBC) remains unknown. Recent evidence indicates that in TNBCs, cells that display "cancer stem cell" properties are resistant to conventional treatments, mediate tumor metastasis, and contribute to recurrence. The sensitivity of breast cancer stem cells (CSC) to PARPi is unknown. EXPERIMENTAL DESIGN: We determined the sensitivity of breast CSCs to PARP inhibition in BRCA1-mutant and -wild-type TNBC cell lines and tumor xenografts. We also investigated the role of RAD51 in mediating CSC resistance to PARPi in these in vitro and in vivo models. RESULTS: We demonstrated that the CSCs in BRCA1-mutant TNBCs were resistant to PARP inhibition, and that these cells had both elevated RAD51 protein levels and activity. Downregulation of RAD51 by shRNA sensitized CSCs to PARP inhibition and reduced tumor growth. BRCA1-wild-type cells were relatively resistant to PARP inhibition alone, but reduction of RAD51 sensitized both CSC and bulk cells in these tumors to PARPi treatment. CONCLUSIONS: Our data suggest that in both BRCA1-mutant and BRCA1-wild-type TNBCs, CSCs are relatively resistant to PARP inhibition. This resistance is mediated by RAD51, suggesting that strategies aimed at targeting RAD51 may increase the therapeutic efficacy of PARPi. Clin Cancer Res; 23(2); 514-22. ©2016 AACR.

A multiplexed marker-based algorithm for diagnosis of carcinoma of unknown primary using circulating tumor cells.

Real-time, single-cell multiplex immunophenotyping of circulating tumor cells (CTCs) is hypothesized to inform diagnosis of tissue of origin in patients with carcinoma of unknown primary (CUP). In 20 to 50% of CUP patients, the primary site remains unidentified, presenting a challenge for clinicians in diagnosis and treatment. We developed a post-CellSearch CTC assay using multiplexed Q-dot or DyLight conjugated antibodies with the goal of detecting multiple markers in single cells within a CTC population. We adapted our approach to size-based CTC enrichment protocols for capturing CTCs and subsequent immunofluorescence (IF) using a minimal set of markers to predict the primary sites for common metastatic tumors. The carcinomas are characterized with cytokeratin 7 (CK7), cytokeratin 20 (CK20), thyroid transcription factor 1 (TTF-1), estrogen receptor (ER) or prostate-specific antigen (PSA. IF has been optimized in cultured tumor cells with individual antibodies, then with conjugated antibodies to form a multiplex antibody set. With IF, we evaluated antibodies specific to these 5 markers in lung, breast, colorectal, and prostate cancer cell lines and blood from metastatic prostate and breast cancer patients. This advanced technology provides a noninvasive, diagnostic blood test as an adjunct to routine tissue biopsy. Its further implementation requires prospective clinical testing.

Circulating tumor cell isolation during resection of colorectal cancer lung and liver metastases: a prospective trial with different detection techniques.

BACKGROUND: Colorectal cancer (CRC) metastasectomy improves survival, however most patient develop recurrences. Circulating tumor cells (CTCs) are an independent prognostic marker in stage IV CRC. We hypothesized that CTCs can be enriched during metastasectomy applying different isolation techniques. METHODS: 25 CRC patients undergoing liver (16 (64%)) or lung (9 (36%)) metastasectomy were prospectively enrolled (clinicaltrial.gov identifier: NCT01722903). Central venous (liver) or radial artery (lung) tumor outflow blood (7.5 ml) was collected at incision, during resection, 30 min after resection, and on postoperative day (POD) 1. CTCs were quantified with 1. EpCAM-based CellSearch® system and 2. size-based isolation with a novel filter device (FMSA). CTCs were immunohistochemically identified using CellSearch®'s criteria (cytokeratin 8/18/19+, CD45- cells containing a nucleus (DAPI+)). CTCs were also enriched with a centrifugation technique (OncoQuick®). RESULTS: CTC numbers peaked during the resection with the FMSA in contrast to CellSearch® (mean CTC number during resection: FMSA: 22.56 (SEM 7.48) (p = 0.0281), CellSearch®: 0.87 (SEM ± 0.44) (p = 0.3018)). Comparing the 2 techniques, CTC quantity was significantly higher with the FMSA device (range 0-101) than CellSearch® (range 0-9) at each of the 4 time points examined (P < 0.05). Immunofluorescence staining of cultured CTCs revealed that CTCs have a combined epithelial (CK8/18/19) and macrophage (CD45/CD14) phenotype. CONCLUSIONS: Blood sampling during CRC metastasis resection is an opportunity to increase CTC capture efficiency. CTC isolation with the FMSA yields more CTCs than the CellSearch® system. Future studies should focus on characterization of single CTCs to identify targets for molecular therapy and immune escape mechanisms of cancer cells.

Circulating tumor cells: advances in isolation and analysis, and challenges for clinical applications.

Circulating tumor cells (CTCs) are rare cancer cells released from tumors into the bloodstream that are thought to have a key role in cancer metastasis. The presence of CTCs has been associated with worse prognosis in several major cancer types, including breast, prostate and colorectal cancer. There is considerable interest in CTC research and technologies for their potential use as cancer biomarkers that may enhance cancer diagnosis and prognosis, facilitate drug development, and improve the treatment of cancer patients. This review provides an update on recent progress in CTC isolation and molecular characterization technologies. Furthermore, the review covers significant advances and limitations in the clinical applications of CTC-based assays for cancer prognosis, response to anti-cancer therapies, and exploratory studies in biomarkers predictive of sensitivity and resistance to cancer therapies.

Separable bilayer microfiltration device for viable label-free enrichment of circulating tumour cells.

The analysis of circulating tumour cells (CTCs) in cancer patients could provide important information for therapeutic management. Enrichment of viable CTCs could permit performance of functional analyses on CTCs to broaden understanding of metastatic disease. However, this has not been widely accomplished. Addressing this challenge, we present a separable bilayer (SB) microfilter for viable size-based CTC capture. Unlike other single-layer CTC microfilters, the precise gap between the two layers and the architecture of pore alignment result in drastic reduction in mechanical stress on CTCs, capturing them viably. Using multiple cancer cell lines spiked in healthy donor blood, the SB microfilter demonstrated high capture efficiency (78-83%), high retention of cell viability (71-74%), high tumour cell enrichment against leukocytes (1.7-2 × 10(3)), and widespread ability to establish cultures post-capture (100% of cell lines tested). In a metastatic mouse model, SB microfilters successfully enriched viable mouse CTCs from 0.4-0.6 mL whole mouse blood samples and established in vitro cultures for further genetic and functional analysis. Our preliminary studies reflect the efficacy of the SB microfilter device to efficiently and reliably enrich viable CTCs in animal model studies, constituting an exciting technology for new insights in cancer research.

Circulating tumor cell enrichment based on physical properties.

The metastatic dissemination and spread of malignant circulating tumor cells (CTCs) accounts for more than 90% of cancer-related deaths. CTCs detach from a primary tumor, travel through the circulatory system, and then invade and proliferate in distant organs. The detection of CTCs from blood has been established for prognostic monitoring and is predictive of patient outcome. Analysis of CTCs could enable the means for early detection and screening in cancer, as well as provide diagnostic access to tumor tissues in a minimally invasive way. The fundamental challenge with analyzing CTCs is the fact that they occur at extremely low concentrations in blood, on the order of one out of a billion cells. Various technologies have been proposed to isolate CTCs for enrichment. Here we focus on antigen-independent approaches that are not limited by specific capture antibodies. Intrinsic physical properties of CTCs, including cell size, deformability, and electrical properties, are reviewed, and technologies developed to exploit them for enrichment from blood are summarized. Physical enrichment technologies are of particular interest as they have the potential to increase yield and enable the analysis of rare CTC phenotypes that may not be otherwise obtained.

Predicting therapy response in live tumor cells isolated with the flexible micro spring array device.

Cells disseminated from primary epithelial tumors into peripheral blood, called circulating tumor cells (CTCs), can be monitored to assess metastases and to provide a surrogate marker of treatment response. Here, we demonstrate how the flexible micro spring array (FMSA) device-a novel microfluidic device that enriches CTCs by two physical parameters: size and deformability-could be used in the rational development of treatment intervention and as a method to study the fundamental biology of CTCs. Cancer cells of different origins were spiked into healthy samples of donor blood to mimic blood samples of metastatic cancer patients. This spiked human blood was filtered using the FMSA device, and the recovered cells were successfully expanded in vitro and in a novel in vivo system. A series of experiments were performed to characterize these cells and to investigate the effect of chemotherapy on the resulting cultures. As few as 20 colon cancer cells in 7.5 mL blood could be isolated with the FMSA device, expanded both in vitro and in vivo and used at 25 cells per well to obtain significant and reliable chemosensitivity data. We also show that isolating a low number of viable patient CTCs and maintaining them in culture for a few weeks is possible. The isolation of viable cancer cells from human blood using the FMSA device provides a novel and realistic means for studying the biology of viable CTCs and for testing drug efficacy on these rare cells-a hypothesis that can be tested in future clinical trials.

Viable circulating tumor cell enrichment by flexible micro spring array.

We demonstrated a high throughput versatile platform capable of isolating circulating tumor cells (CTCs) from clinically relevant volumes of blood while preserving their viability and ability to proliferate. The enrichment is based on the fact that CTCs are larger compared with normal blood cells. The incorporated system allows size-based separation of CTCs at the micro-scale, while taking advantage of a high throughput and rapid processing speed. Testing results of model systems using cell lines show that this device can enrich CTCs from 7.5 mL of whole blood samples with 90% capture efficiency, higher than 10(4) enrichment, and better than 80% viability in approximately ten minutes without any incidence of clogging.

Circulating tumor cells in melanoma patients.

Circulating tumor cells (CTCs) are of recognized importance for diagnosis and prognosis of cancer patients. With melanoma, most studies do not show any clear relationship between CTC levels and stage of disease. Here, CTCs were enriched (∼400X) from blood of melanoma patients using a simple centrifugation device (OncoQuick), and 4 melanocyte target RNAs (TYR, MLANA, MITF, and MIF) were quantified using QPCR. Approximately one-third of melanoma patients had elevated MIF and MLANA transcripts (p<0.0001 and p<0.001, respectively) compared with healthy controls. In contrast, healthy controls had uniformly higher levels of TYR and MITF than melanoma patients (p<0.0001). There was a marked shift of leukocytes into the CTC-enriched fractions (a 430% increase in RNA recovery, p<0.001), and no relationship between CTC levels and stage of disease was found. CTCs were captured on microfabricated filters and cultured. Captured melanoma CTCs were large cells, and consisted of 2 subpopulations, based on immunoreactivity. One subpopulation (∼50%) stained for both pan-cytokeratin (KRT) markers and the common leukocyte marker CD-45, whereas the second subpopulation stained for only KRT. Since similar cells are described in many cancers, we also examined blood from colorectal and pancreatic cancer patients. We observed analogous results, with most captured CTCs staining for both CD-45/KRT markers (and for the monocyte differentiation marker CD-14). Our results suggest that immature melanocyte-related cells (expressing TYR and MITF RNA) may circulate in healthy controls, although they are not readily detectable without considerable enrichment. Further, as early-stage melanomas develop, immature melanocyte migration into the blood is somehow curtailed, whereas a significant proportion of patients develop elevated CTC levels (based on MIF and MLANA RNAs). The nature of the captured CTCs is consistent with literature describing leukocyte/macrophage-tumor cell fusion hybrids, and their role in metastatic progression.