Cancer micrometastasis and tumour dormancy

Tumor Dormancy and Reactivation: The Role of Heat Shock Proteins

Tumors are a heterogeneous group of cell masses originating in various organs or tissues. The cellular composition of the tumor cell mass interacts in an intricate manner, influenced by humoral, genetic, molecular, and tumor microenvironment cues that dictate tumor growth or suppression. As a result, tumors undergo a period of a dormant state before their clinically discernible stage, which surpasses the clinical dormancy threshold. Moreover, as a genetically imprinted strategy, early-seeder cells, a distinct population of tumor cells, break off to dock nearby or extravasate into blood vessels to secondary tissues, where they form disseminated solitary dormant tumor cells with reversible capacity. Among the various mechanisms underlying the dormant tumor mass and dormant tumor cell formation, heat shock proteins (HSPs) might play one of the most important roles in how the dormancy program plays out. It is known that numerous aberrant cellular processes, such as malignant transformation, cancer cell stemness, tumor invasion, metastasis, angiogenesis, and signaling pathway maintenance, are influenced by the HSPs. An accumulating body of knowledge suggests that HSPs may be involved in the angiogenic switch, immune editing, and extracellular matrix (ECM) remodeling cascades, crucial genetically imprinted strategies important to the tumor dormancy initiation and dormancy maintenance program. In this review, we highlight the biological events that orchestrate the dormancy state and the body of work that has been conducted on the dynamics of HSPs in a tumor mass, as well as tumor cell dormancy and reactivation. Additionally, we propose a conceptual framework that could possibly underlie dormant tumor reactivation in metastatic relapse.

Prognostic role of lymph node micrometastasis in pN0 esophageal cancer: A meta-analysis

BACKGROUND

To further identify the association between the lymph node micrometastasis (LNM) and long-term survival among pN0 esophageal cancer patients receiving the surgery.

METHODS

Several databases were searched for relevant studies up to June 22, 2023. The primary and secondary outcomes were separately overall survival (OS) and relapse-free survival (RFS) and hazard ratios (HRs) with 95% confidence intervals (CIs) were combined. Subgroup analysis based on pathological type and source of HR was further performed. All statistical analyses were conducted by STATA 15.0 software.

RESULTS

A total of 20 studies involving 1830 pN0 patients were included in this meta-analysis. The pooled results demonstrated that the presence of LNM indicated significantly worse OS (HR = 2.19, 95% CI = 1.77-2.70, P < .001) and RFS (HR = 2.15, 95% CI = 1.65-2.80, P < .001). Besides, subgroup analysis for the OS and RFS stratified by the pathological type (squamous cell carcinoma vs mixed esophageal cancer) and source of HR (reported vs estimated) further identified the significant relationship of LNM with prognosis in surgical esophageal cancer.

CONCLUSION

The presence of LNM indicated significantly poorer long-term survival among operated pN0 esophageal cancer patients. LNM could serve as a novel and reliable prognostic indicator in surgical esophageal cancer.

The Role of TAM Receptors in Bone

The TAM (TYRO3, MERTK, and AXL) family of receptor tyrosine kinases are pleiotropic regulators of adult tissue homeostasis maintaining organ integrity and self-renewal. Disruption of their homeostatic balance fosters pathological conditions like autoinflammatory or degenerative diseases including rheumatoid arthritis, lupus erythematodes, or liver fibrosis. Moreover, TAM receptors exhibit prominent cell-transforming properties, promoting tumor progression, metastasis, and therapy resistance in various cancer entities. Emerging evidence shows that TAM receptors are involved in bone homeostasis by regulating osteoblastic bone formation and osteoclastic bone resorption. Therefore, TAM receptors emerge as new key players of the regulatory cytokine network of osteoblasts and osteoclasts and represent accessible targets for pharmacologic therapy for a broad set of different bone diseases, including primary and metastatic bone tumors, rheumatoid arthritis, or osteoporosis.

Quantification of circulating tumour cells over time in dogs with appendicular osteosarcoma

Enumeration of circulating tumour cells (CTC) has shown promise for prognostication and guidance of therapeutic decisions in human cancers. The objective of this study was to enumerate CTC over time in dogs with naturally occurring osteosarcoma (OSA), and to determine correlation with patient outcome. Twenty-six dogs with OSA and no evidence of metastatic disease at the time of amputation were enrolled. Dogs were assessed for lung metastases and CTC prior to and following amputation, and at each chemotherapy visit. Twenty-one dogs completed the study. Nineteen dogs were euthanized and two were alive and free of metastases. Overall survival time ranged from 88 to 1058 days (median survival time (MST) 374 days). Increased serum alkaline phosphatase activity, advanced age, and higher body weight were significantly associated with lower MST. Dogs with OSA had a mean of 356 (0 to 4443) CTC/106 leukocytes. In 12 of 15 dogs that developed radiographic evidence of metastasis, a pre-metastatic CTC spike was retrospectively detectable on average 36.5 (1-100 days) days prior to metastasis and was associated with significantly shorter MST (301 ± 64 vs. 626 ± 55 days; p = .0107). In a multivariable analysis, dogs with a CTC spike were 10× more likely to die compared with those without. These results suggest that a spike in CTC frequency precedes detection of metastasis in dogs with OSA and is associated with shorter survival. More frequent enumeration of CTC in a larger cohort of dogs with OSA may be warranted.

KISS1 metastasis suppressor in tumor dormancy: a potential therapeutic target for metastatic cancers?

Present therapeutic approaches do not effectively target metastatic cancers, often limited by their inability to eliminate already-seeded non-proliferative, growth-arrested, or therapy-resistant tumor cells. Devising effective approaches targeting dormant tumor cells has been a focus of cancer clinicians for decades. However, progress has been limited due to limited understanding of the tumor dormancy process. Studies on tumor dormancy have picked up pace and have resulted in the identification of several regulators. This review focuses on KISS1, a metastasis suppressor gene that suppresses metastasis by keeping tumor cells in a state of dormancy at ectopic sites. The review explores mechanistic insights of KISS1 and discusses its potential application as a therapeutic against metastatic cancers by eliminating quiescent cells or inducing long-term dormancy in tumor cells.

Mechanisms of cancer metastasis

Metastatic cancer is almost always terminal, and more than 90% of cancer deaths result from metastatic disease. Combating cancer metastasis and post-therapeutic recurrence successfully requires understanding each step of metastatic progression. This review describes the current state of knowledge of the etiology and mechanism of cancer progression from primary tumor growth to the formation of new tumors in other parts of the body. Open questions, avenues for future research, and therapeutic approaches with the potential to prevent or inhibit metastasis through personalization to each patient's mutation and/or immune profile are also highlighted.

Molecular mechanisms of cancer metastasis via the lymphatic versus the blood vessels

Cancer metastasis is the process by which primary cancer cells invade through the lymphatic or blood vessels to distant sites. The molecular mechanisms by which cancer cells spread either through the lymphatic versus blood vessels or both are not well established. Two major developments have helped us to understand the process more clearly. First, the development of the sentinel lymph node (SLN) concept which is well established in melanoma and breast cancer. The SLN is the first lymph node in the draining nodal basin to receive cancer cells. Patients with a negative SLN biopsy show a significantly lower incidence of distant metastasis, suggesting that the SLN may be the major gateway for cancer metastasis in these cancer types. Second, the discovery and characterization of several biomarkers including VEGF-C, LYVE-1, Podoplanin and Prox-1 have opened new vistas in the understanding of the induction of lymphangiogenesis by cancer cells. Cancer cells must complete multiple steps to invade the lymphatic system, some of which may be enabled by the evolution of new traits during cancer progression. Thus, cancer cells may spread initially through the main gateway of the SLN, from which evolving cancer clones can invade the blood vessels to distant sites. Cancer cells may also enter the blood vessels directly, bypassing the SLN to establish distant metastases. Future studies need to pinpoint the molecules that are used by cancer cells at different stages of metastasis via different routes so that specific therapies can be targeted against these molecules, with the goal of stopping or preventing cancer metastasis.

Doxorubicin-Resistant TNBC Cells Exhibit Rapid Growth with Cancer Stem Cell-like Properties and EMT Phenotype, Which Can Be Transferred to Parental Cells through Autocrine Signaling

Emerging evidence suggests that breast cancer stem cells (BCSCs), and epithelial-mesenchymal transition (EMT) may be involved in resistance to doxorubicin. However, it is unlear whether the doxorubicin-induced EMT and expansion of BCSCs is related to cancer dormancy, or outgrowing cancer cells with maintaining resistance to doxorubicin, or whether the phenotypes can be transferred to other doxorubicin-sensitive cells. Here, we characterized the phenotype of doxorubicin-resistant TNBC cells while monitoring the EMT process and expansion of CSCs during the establishment of doxorubicin-resistant MDA-MB-231 human breast cancer cells (DRM cells). In addition, we assessed the potential signaling associated with the EMT process and expansion of CSCs in doxorubicin-resistance of DRM cells. DRM cells exhibited morphological changes from spindle-shaped MDA-MB-231 cells into round-shaped giant cells. They exhibited highly proliferative, EMT, adhesive, and invasive phenotypes. Molecularly, they showed up-regulation of Cyclin D1, mesenchymal markers (β-catenin, and N-cadherin), MMP-2, MMP-9, ICAM-1 and down-regulation of E-cadherin. As the molecular mechanisms responsible for the resistance to doxorubicin, up-regulation of EGFR and its downstream signaling, were suggested. AKT and ERK1/2 expression were also increased in DRM cells with the advancement of resistance to doxorubicin. Furthermore, doxorubicin resistance of DRM cells can be transferred by autocrine signaling. In conclusion, DRM cells harbored EMT features with CSC properties possessing increased proliferation, invasion, migration, and adhesion ability. The doxorubicin resistance, and doxorubicin-induced EMT and CSC properties of DRM cells, can be transferred to parental cells through autocrine signaling. Lastly, this feature of DRM cells might be associated with the up-regulation of EGFR.

Cellular dormancy in minimal residual disease following targeted therapy

BACKGROUND

Breast cancer mortality is principally due to tumor recurrence, which can occur following extended periods of clinical remission that may last decades. While clinical latency has been postulated to reflect the ability of residual tumor cells to persist in a dormant state, this hypothesis remains unproven since little is known about the biology of these cells. Consequently, defining the properties of residual tumor cells is an essential goal with important clinical implications for preventing recurrence and improving cancer outcomes.

METHODS

To identify conserved features of residual tumor cells, we modeled minimal residual disease using inducible transgenic mouse models for HER2/neu and Wnt1-driven tumorigenesis that recapitulate cardinal features of human breast cancer progression, as well as human breast cancer cell xenografts subjected to targeted therapy. Fluorescence-activated cell sorting was used to isolate tumor cells from primary tumors, residual lesions following oncogene blockade, and recurrent tumors to analyze gene expression signatures and evaluate tumor-initiating cell properties.

RESULTS

We demonstrate that residual tumor cells surviving oncogenic pathway inhibition at both local and distant sites exist in a state of cellular dormancy, despite adequate vascularization and the absence of adaptive immunity, and retain the ability to re-enter the cell cycle and give rise to recurrent tumors after extended latency periods. Compared to primary or recurrent tumor cells, dormant residual tumor cells possess unique features that are conserved across mouse models for human breast cancer driven by different oncogenes, and express a gene signature that is strongly associated with recurrence-free survival in breast cancer patients and similar to that of tumor cells in which dormancy is induced by the microenvironment. Although residual tumor cells in both the HER2/neu and Wnt1 models are enriched for phenotypic features associated with tumor-initiating cells, limiting dilution experiments revealed that residual tumor cells are not enriched for cells capable of giving rise to primary tumors, but are enriched for cells capable of giving rise to recurrent tumors, suggesting that tumor-initiating populations underlying primary tumorigenesis may be distinct from those that give rise to recurrence following therapy.

CONCLUSIONS

Residual cancer cells surviving targeted therapy reside in a well-vascularized, desmoplastic microenvironment at both local and distant sites. These cells exist in a state of cellular dormancy that bears little resemblance to primary or recurrent tumor cells, but shares similarities with cells in which dormancy is induced by microenvironmental cues. Our observations suggest that dormancy may be a conserved response to targeted therapy independent of the oncogenic pathway inhibited or properties of the primary tumor, that the mechanisms underlying dormancy at local and distant sites may be related, and that the dormant state represents a potential therapeutic target for preventing cancer recurrence.

Low RAI2 expression is a marker of poor prognosis in breast cancer

PURPOSE

Retinoic acid-induced 2 (RAI2) has been shown to be a putative suppressor of the early hematogenous dissemination of tumor cells to the bone marrow in breast cancer. Here, we investigated the associations of RAI2 mRNA and protein expression with clinicopathological factors and prognosis in breast cancer patients with long-term follow-up.

METHODS

Invasive breast cancer tissues (n = 604) were analyzed for RAI2 mRNA expression. We examined the associations of clinicopathological factors with the expression levels of RAI2 mRNA in these samples. We also analyzed RAI2 protein expression by immunohistochemistry in invasive breast cancer tissues (n = 422).

RESULTS

We identified significant positive associations between low expression of RAI2 mRNA and shorter disease-free survival (DFS), breast-cancer-specific survival (BCSS), and overall survival (OS) in breast cancer patients. We also identified significant positive associations between negative for RAI2 protein expression and shorter DFS, BCSS, and OS in breast cancer patients. Low RAI2 mRNA and negative for RAI2 protein expression were positively associated with larger tumor size, higher tumor grade, and ERα-negativity. Multivariate analyses indicated that not only RAI2 mRNA but also RAI2 protein expression were independent risk factors for both DFS and BCSS in breast cancer patients. The median follow-up periods were 10.3 and 9.3 years for the RAI2 mRNA and protein expression analyses, respectively.

CONCLUSIONS

Our findings suggest that RAI2 has a role in the metastasis of breast cancer, and that RAI2 expression could be a promising candidate biomarker of prognosis in breast cancer patients.

Single-Cell NGS-Based Analysis of Copy Number Alterations Reveals New Insights in Circulating Tumor Cells Persistence in Early-Stage Breast Cancer

Simple Summary

Circulating tumor cells (CTCs) are crucial for the identification of patients with a higher risk of relapse, including those diagnosed with breast cancer (BC). The aim of this study was to explore their molecular aspects in 11 early-stage BC patients during patient management, focusing on copy number alterations (CNAs) and exploiting a single-CTC next-generation sequencing approach. CTCs showed different degrees of aberration based on access time. Moreover, CTCs, in particular those persisting even months after tumor resection, shared CNAs with matched tumor tissue. Enrichment analyses of CNAs on CTCs highlighted peculiar aberrations, especially associated with interferon (IFN)-associated terms. The study of CTCs CNAs can provide information about the molecular mechanisms involving CTC-related processes and their survival ability in occult niches, supporting the goal of exploiting their application in patients’ surveillance and follow-up.

Abstract

Circulating tumor cells (CTCs) are a rare population of cells representing a key player in the metastatic cascade. They are recognized as a validated tool for the identification of patients with a higher risk of relapse, including those diagnosed with breast cancer (BC). However, CTCs are characterized by high levels of heterogeneity that also involve copy number alterations (CNAs), structural variations associated with gene dosage changes. In this study, single CTCs were isolated from the peripheral blood of 11 early-stage BC patients at different time points. A label-free enrichment of CTCs was performed using OncoQuick, and single CTCs were isolated using DEPArray. Libraries were prepared from single CTCs and DNA extracted from matched tumor tissues for a whole-genome low-coverage next-generation sequencing (NGS) analysis using the Ion Torrent S5 System. The analysis of the CNA burden highlighted that CTCs had different degrees of aberration based on the time point and subtype. CTCs were found even six months after surgery and shared CNAs with matched tumor tissue. Tumor-associated CNAs that were recurrent in CTCs were patient-specific, and some alterations involved regions associated with BC and survival (i.e., gains at 1q21-23 and 5p15.33). The enrichment analysis emphasized the involvement of aberrations of terms, associated in particular with interferon (IFN) signaling. Collectively, our findings reveal that these aberrations may contribute to understanding the molecular mechanisms involving CTC-related processes and their survival ability in occult niches, supporting the goal of exploiting their application in patients’ surveillance and follow-up.

Reciprocal Interplay Between Fibrillar Collagens and Collagen-Binding Integrins: Implications in Cancer Progression and Metastasis

Cancers are complex ecosystems composed of malignant cells embedded in an intricate microenvironment made of different non-transformed cell types and extracellular matrix (ECM) components. The tumor microenvironment is governed by constantly evolving cell-cell and cell-ECM interactions, which are now recognized as key actors in the genesis, progression and treatment of cancer lesions. The ECM is composed of a multitude of fibrous proteins, matricellular-associated proteins, and proteoglycans. This complex structure plays critical roles in cancer progression: it functions as the scaffold for tissues organization and provides biochemical and biomechanical signals that regulate key cancer hallmarks including cell growth, survival, migration, differentiation, angiogenesis, and immune response. Cells sense the biochemical and mechanical properties of the ECM through specialized transmembrane receptors that include integrins, discoidin domain receptors, and syndecans. Advanced stages of several carcinomas are characterized by a desmoplastic reaction characterized by an extensive deposition of fibrillar collagens in the microenvironment. This compact network of fibrillar collagens promotes cancer progression and metastasis, and is associated with low survival rates for cancer patients. In this review, we highlight how fibrillar collagens and their corresponding integrin receptors are modulated during cancer progression. We describe how the deposition and alignment of collagen fibers influence the tumor microenvironment and how fibrillar collagen-binding integrins expressed by cancer and stromal cells critically contribute in cancer hallmarks.

Dormancy and NKG2D system in brain metastases: Analysis of immunogenicity

Patients with breast cancer (BC) and lung cancer (LC) are prone to developing brain metastases, which are associated with devastating prognoses. Dormant tumor cells, a population of non-apoptotic quiescent cells and immunological escape mechanisms, including the Natural Killer Group 2 member D (NKG2D) receptor-ligand system, represent potential mechanisms of tumor recurrence. To date, the immunological characteristics of dormant tumor cells concerning the NKG2D system in cerebral malignancies are mostly unknown. In the present study, an extensive characterization of dormant and NKG2D ligand (NKG2DL)⁺ cells in cerebral metastases was performed. The expression profiles and localization patterns of various NKG2DL and several dormancy markers were analyzed in solid human brain metastases from patients with BC and LC using immunostaining and reverse transcription-quantitative polymerase chain reaction analyses. Statistical analysis was performed using Student's t-test and Bravais-Pearson correlation analysis. Not only 'peripheral', but also 'central' dormancy markers, which had been previously described in primary brain tumors, were identified in all cerebral metastases at detectable levels at protein and mRNA levels. Notably, the majority of NKG2DL⁺ cells were also positive for 'central' dormancy markers, but not 'peripheral' dormancy markers in both patient groups. This cell population may represent a promising future therapeutic target.

Cancer Ecology and Evolution: Positive interactions and system vulnerability

Parallels of cancer with ecology and evolution have provided new insights into the initiation and spread of cancer, and new approaches to therapy. This review describes those parallels while emphasizing some key contrasts. We argue that cancers are less like invasive species than like native species or even crops that have escaped control, and that ecological control and homeo-static control differ fundamentally through both their ends and their means. From our focus on the role of positive interactions in control processes, we introduce a novel mathematical modeling framework that tracks how individual cell lineages arise, and how the many layers of control break down in the emergence of cancer. The next generation of therapies must continue to look beyond cancers as being created by individual renegade cells and address not only the network of interactions those cells inhabit, but the evolutionary logic that created those interactions and their intrinsic vulnerability.

Dormant disseminated tumor cells and cancer stem/progenitor-like cells: Similarities and opportunities

Distant recurrences occurring years after removal of the primary tumor arise from disseminated tumor cells (DTCs) that lie dormant (quiescent/asymptomatic) until they emerge to overt metastases. These quiescent DTCs are resistant to conventional treatments. Hence, to date there is no available treatment which targets dormant DTCs before they form overt metastases. Therefore, understanding the biology of dormant DTCs and the mechanisms of their reactivation is vital in our pursuit to develop therapies to prevent cancer from ever recurring. This review will address the striking similarities between the biology of DTCs and the biology of cancer stem cells (CSCs) or CSC-like cells including cancer progenitor-like cells. These similarities are related to intrinsic mechanisms of survival and quiescence, and their cross-talk with mediators, produced in their surrounding niches that may support either dormancy or outgrowth. Unraveling these similarities may provide us with exciting opportunities to either mitigate the survival of residing dormant DTCs/CSCs or maintain them in a dormant state. Whether the stemness properties of CSCs/cancer progenitor-like cells already comprising the recurring tumor can be exploited in order to differentiate them, and thus promote their dormancy, will be explored as well. Overall, these emerging concepts may provide us with new opportunities to prevent lethal recurrences.

Cell-to-cell influence on growth in large populations

Recent studies have revealed the importance of outlier cells in complex cellular systems. Quantifying heterogeneity in such systems may lead to a better understanding of organ engineering, microtumor growth, and disease models, as well as more precise drug design. We used the ability of quantitative phase imaging to perform long-term imaging of cell growth to estimate the "influence" of cellular clusters on their neighbors. We validated our approach by analyzing epithelial and fibroblast cultures imaged over the course of several days. Interestingly, we found that there is a significant number of cells characterized by a medium correlation between their growth rate and distance (modulus of the Pearson coefficient between 0.25-.5). Furthermore, we found a small percentage of cells exhibiting strong such correlations, which we label as "influencer" cellular clusters. Our approach might find important applications in studying dynamic phenomena, such as organogenesis and metastasis.

The role of SOX family members in solid tumours and metastasis

Cancer is a heavy burden for humans across the world with high morbidity and mortality. Transcription factors including sex determining region Y (SRY)-related high-mobility group (HMG) box (SOX) proteins are thought to be involved in the regulation of specific biological processes. The deregulation of gene expression programs can lead to cancer development. Here, we review the role of the SOX family in breast cancer, prostate cancer, renal cell carcinoma, thyroid cancer, brain tumours, gastrointestinal and lung tumours as well as the entailing therapeutic implications. The SOX family consists of more than 20 members that mediate DNA binding by the HMG domain and have regulatory functions in development, cell-fate decision, and differentiation. SOX2, SOX4, SOX5, SOX8, SOX9, and SOX18 are up-regulated in different cancer types and have been found to be associated with poor prognosis, while the up-regulation of SOX11 and SOX30 appears to be favourable for the outcome in other cancer types. SOX2, SOX4, SOX5 and other SOX members are involved in tumorigenesis, e.g. SOX2 is markedly up-regulated in chemotherapy resistant cells. The SoxF family (SOX7, SOX17, SOX18) plays an important role in angio- and lymphangiogenesis, with SOX18 seemingly being an attractive target for anti-angiogenic therapy and the treatment of metastatic disease in cancer. In summary, SOX transcription factors play an important role in cancer progression, including tumorigenesis, changes in the tumour microenvironment, and metastasis. Certain SOX proteins are potential molecular markers for cancer prognosis and putative potential therapeutic targets, but further investigations are required to understand their physiological functions.

Engineered In Vitro Models of Tumor Dormancy and Reactivation

Metastatic recurrence is a major hurdle to overcome for successful control of cancer-associated death. Residual tumor cells in the primary site, or disseminated tumor cells in secondary sites, can lie in a dormant state for long time periods, years to decades, before being reactivated into a proliferative growth state. The microenvironmental signals and biological mechanisms that mediate the fate of disseminated cancer cells with respect to cell death, single cell dormancy, tumor mass dormancy and metastatic growth, as well as the factors that induce reactivation, are discussed in this review. Emphasis is placed on engineered, in vitro, biomaterial-based approaches to model tumor dormancy and subsequent reactivation, with a focus on the roles of extracellular matrix, secondary cell types, biochemical signaling and drug treatment. A brief perspective of molecular targets and treatment approaches for dormant tumors is also presented. Advances in tissue-engineered platforms to induce, model, and monitor tumor dormancy and reactivation may provide much needed insight into the regulation of these processes and serve as drug discovery and testing platforms.

Analysis of circulating tumor DNA in breast cancer as a diagnostic and prognostic biomarker

Despite all the advances in diagnosis and treatment of breast cancer, a large number of patients suffer from late diagnosis or recurrence of their disease. Current available imaging modalities do not reveal micrometastasis and tumor biopsy is an invasive method to detect early stage or recurrent cancer, signifying the need for an inexpensive, non-invasive diagnostic modality. Cell-free tumor DNA (ctDNA) has been tried for early detection and targeted therapy of breast cancer, but its diagnostic and prognostic utility is still under investigation. This review summarizes the existing evidence on the use of ctDNA specifically in breast cancer, including detection methods, diagnostic accuracy, role in genetics and epigenetics evaluation of the tumor, and comparison with other biomarkers. Current evidence suggests that increasing levels of ctDNA in breast cancer can be of significant diagnostic value for early detection of breast cancer although the sensitivity and specificity of the methods is still suboptimal. Additionally, ctDNA allows for characterizing the tumor in a non-invasive way and monitor the response to therapy, although discordance of ctDNA results with direct biopsy (i.e. due to tumor heterogeneity) is still considered a notable limitation.

METCAM/MUC18 Decreases the Malignant Propensity of Human Ovarian Carcinoma Cells

METCAM/MUC18 is an integral membrane cell adhesion molecule (CAM) in the Ig-like gene super-family. It can carry out common functions of CAMs which is to perform intercellular interactions and interaction of cell with extracellular matrix in tumor microenvironment, to interact with various signaling pathways and to regulate general behaviors of cells. We and other two groups previously suggested that METCAM/MUC18 probably be utilized as a biomarker for predicting the malignant tendency of clinical ovarian carcinomas, since METAM/MUC18 expression appears to associate with the carcinoma at advanced stages. It has been further postulated to promote the malignant tendency of the carcinoma. However, our recent research results appear to support the conclusion that the above positive correlation is fortuitous; actually METCAM/MUC18 acts as a tumor and metastasis suppressor for the ovarian carcinoma cells. We also suggest possible mechanisms in the METCAM/MUC18-mediated early tumor development and metastasis of ovarian carcinoma. Moreover, we propose to employ recombinant METCAM/MUC18 proteins and other derived products as therapeutic agents to treat the ovarian cancer patients by decreasing the malignant potential of ovarian carcinoma.

EMT and Stemness in Tumor Dormancy and Outgrowth: Are They Intertwined Processes?

Metastases are the major cause of cancer patients' mortality and can occur years and even decades following apparently successful treatment of the primary tumor. Early dissemination of cancer cells, followed by a protracted period of dormancy at distant sites, has been recently recognized as the clinical explanation for this very-long latency. The mechanisms that govern tumor dormancy at distant sites and their reactivation to proliferating metastases are just beginning to be unraveled. Tumor cells, that survive the immune surveillance and hemodynamic forces along their journey in the circulation and successfully colonize and adopt to the new and "hostile" microenvironment and survive in a quiescent dormant state for years before emerging to proliferative state, must display high plasticity. Here we will discuss whether the plasticity of dormant tumor cells is required for their long-term survival and outgrowth. Specifically, we will focus on whether epithelial mesenchymal transition and acquisition of stem-like properties can dictate their quiescent and or their proliferative fate. Deeper understanding of these intertwining processes may facilitate in the future the development of novel therapies.

Cancer Metastases to Bone: Concepts, Mechanisms, and Interactions with Bone Osteoblasts

The skeleton is a unique structure capable of providing support for the body. Bone resorption and deposition are controlled in a tightly regulated balance between osteoblasts and osteoclasts with no net bone gain or loss. However, under conditions of disease, the balance between bone resorption and deposition is upset. Osteoblasts play an important role in bone homeostasis by depositing new bone osteoid into resorption pits. It is becoming increasingly evident that osteoblasts additionally play key roles in cancer cell dissemination to bone and subsequent metastasis. Our laboratory has evidence that when osteoblasts come into contact with disseminated breast cancer cells, the osteoblasts produce factors that initially reduce breast cancer cell proliferation, yet promote cancer cell survival in bone. Other laboratories have demonstrated that osteoblasts both directly and indirectly contribute to dormant cancer cell reactivation in bone. Moreover, we have demonstrated that osteoblasts undergo an inflammatory stress response in late stages of breast cancer, and produce inflammatory cytokines that are maintenance and survival factors for breast cancer cells and osteoclasts. Advances in understanding interactions between osteoblasts, osteoclasts, and bone metastatic cancer cells will aid in controlling and ultimately preventing cancer cell metastasis to bone.

A history of exploring cancer in context

The concept that progression of cancer is regulated by interactions of cancer cells with their microenvironment was postulated by Stephen Paget over a century ago. Contemporary tumour microenvironment (TME) research focuses on the identification of tumour-interacting microenvironmental constituents, such as resident or infiltrating non-tumour cells, soluble factors and extracellular matrix components, and the large variety of mechanisms by which these constituents regulate and shape the malignant phenotype of tumour cells. In this Timeline article, we review the developmental phases of the TME paradigm since its initial description. While illuminating controversies, we discuss the importance of interactions between various microenvironmental components and tumour cells and provide an overview and assessment of therapeutic opportunities and modalities by which the TME can be targeted.

Risk of recurrence and death in patients with breast cancer after delayed deep inferior epigastric perforator flap reconstruction

Background

Postmastectomy reconstruction using a deep inferior epigastric perforator (DIEP) flap is increasingly being performed in patients with breast cancer. The procedure induces extensive tissue trauma, and it has been hypothesized that the release of growth factors, angiogenic agonists and immunomodulating factors may reactivate dormant micrometastasis. The aim of the present study was to estimate the risk of breast cancer recurrence in patients undergoing DIEP flap reconstruction compared with that in patients treated with mastectomy alone.

Methods

Each patient who underwent delayed DIEP flap reconstruction at Karolinska University Hospital, Sweden, between 1999 and 2013, was compared with up to four controls with breast cancer who did not receive a DIEP flap. The control patients were selected using incidence density matching with respect to age, tumour and nodal status, neoadjuvant therapy and year of mastectomy. The primary endpoint was breast cancer‐specific survival. Survival analysis was carried out using Kaplan–Meier survival estimates and Cox proportional hazard regression analysis.

Results

The analysis included 250 patients who had 254 DIEP flap reconstructions and 729 control patients. Median follow‐up was 89 and 75 months respectively (P = 0·053). Breast cancer recurrence developed in 50 patients (19·7 per cent) in the DIEP group and 174 (23·9 per cent) in the control group (P = 0·171). The 5‐year breast cancer‐specific survival rate was 92·0 per cent for patients with a DIEP flap and 87·9 per cent in controls (P = 0·032). Corresponding values for 5‐year overall survival were 91·6 and 84·7 per cent (P < 0·001). After adjustment for tumour and patient characteristics and treatment, patients without DIEP flap reconstruction had significantly lower overall but not breast cancer‐specific survival.

Conclusion

The present findings do not support the hypothesis that patients with breast cancer undergoing DIEP flap reconstruction have a higher rate of breast cancer recurrence than those who have mastectomy alone.

Deep inferior epigastric perforator is safe

Modeling treatment-dependent glioma growth including a dormant tumor cell subpopulation

Background

Tumors comprise a variety of specialized cell phenotypes adapted to different ecological niches that massively influence the tumor growth and its response to treatment.

Methods

In the background of glioblastoma multiforme, a highly malignant brain tumor, we consider a rapid proliferating phenotype that appears susceptible to treatment, and a dormant phenotype which lacks this pronounced proliferative ability and is not affected by standard therapeutic strategies. To gain insight in the dynamically changing proportions of different tumor cell phenotypes under different treatment conditions, we develop a mathematical model and underline our assumptions with experimental data.

Results

We show that both cell phenotypes contribute to the distinct composition of the tumor, especially in cycling low and high dose treatment, and therefore may influence the tumor growth in a phenotype specific way.

Conclusion

Our model of the dynamic proportions of dormant and rapidly growing glioblastoma cells in different therapy settings suggests that phenotypically different cells should be considered to plan dose and duration of treatment schedules.

Metastases of malignant neoplasms: Historical, biological, & clinical considerations

The metastasis of neoplastic cells from their site of origin to distant anatomic locations continues to be the principal cause of death from malignant tumors, and that fact has been recognized by physicians for over a century. After the work done by Halsted in the treatment of breast cancer in the 1880s, accepted surgical canon held that metastasis occurred in a linear fashion, with centrifugal "growth in continuity" from the primary neoplasm that first involved regional lymph nodes. Those structures were considered to then be the sources of more distant, visceral metastases. With that premise in mind, radical and "ultra-radical" surgical procedures were devised to remove as many lymph nodes as possible in the treatment of carcinomas and melanomas. However, such interventions were ineffective in altering tumor-related mortality. This review considers the details of the historical material just mentioned. It also reviews currently-held concepts on biological mechanisms of metastasis, the "sentinel" lymph node biopsy technique, and the important topic of metastatic tumor "dormancy" as the cause of surgical treatment failure. Finally, predictive models of tumor behavior are discussed, which are based on gene signatures. These will likely be the key to identifying malignant lesions of low surgical stage that ultimately prove fatal through later manifestation of metastasis.

Molecular Profiling and Significance of Circulating Tumor Cell Based Genetic Signatures

Cancer kills by metastasizing beyond the primary site. Early detection, surgical intervention and other treatments have improved the survival rates of patients with cancer, however, once metastasis occurs, responses to conventional therapies become significantly less effective, and this remains the leading cause of death. Circulating tumor cells (CTCs) are tumor cells that have preferentially disseminated from the primary tumor mass into the hematological system, and are en route to favorable distant sites where if they survive, can develop into metastases. They may be the earliest detectable cells with metastatic ability, and are gaining increasing attention because of their prognostic value in many types of cancers including breast, prostate, colon and lung. Recent technological advances have removed barriers that previously hindered the detection and isolation of these rare cells from blood, and have exponentially improved the genetic resolution at which we can characterize signatures that define CTCs. Some of the most significant observations from such examinations are described here. Firstly, aberrations that were thought to be unique to CTCs are detected at subclonal frequencies within primary tumors with measurable heterogeneity, indicating pre-existing genetic signatures for metastasis. Secondly, these subclonal events are enriched in CTCs and metastases, pointing towards the selection of a more 'fit' component of tumor cells with survival advantages. Lastly, this component of cancer cells may also be the chemoresistant portion that escapes systemic treatment, or acquires resistance during progression of the disease. The future of cancer management may include a standardized method of measuring intratumor heterogeneity of the primary as well as matched CTCs. This will help identify and target rare aberrations within primary tumors that make them more adept to disseminate, and also to monitor the development of treatment resistant subclones as cancer progresses.

Increased kinetic growth rate during late phase liver regeneration impacts the risk of tumor recurrence after colorectal liver metastases resection

BACKGROUND

Although experimental data strongly support the pro-tumorigenic role of postoperative liver regeneration, this hypothesis has not been clinically investigated. We aimed to examine the impact of liver regeneration determined by volumetric imaging on recurrence following resection of colorectal liver metastasis (CRLM).

METHODS

Resected liver volume was subtracted from total liver volume (TLV) to define postoperative remnant liver volume (RLV_p). Early and late kinetic growth rates (KGR) were defined as the postoperative increases in liver volume within 2-3 and 8-10 months from surgery, respectively, divided by the corresponding time interval.

RESULTS

Median early and late KGR was 2.6%/month (IQR: -0.9 to 12.3) and 1.0%/month (IQR: -0.64 to 2.91), respectively. Late KGR predicted intrahepatic recurrence after 1 year from surgery (AUC 0.677, P = 0.011). Specifically, patients with a late KGR ≥1% had a higher cumulative risk of recurrence compared with patients with a KGR <1% (P = 0.038). In multivariate analysis, KGR ≥1% independently predicted recurrence (P = 0.027).

DISCUSSION

A KGR ≥1% during the late regeneration phase was associated with increased risk of intrahepatic recurrence. These data may inform the timing of adjuvant therapy administration and focus surveillance strategies for high-risk patients.

Challenges and unanswered questions for the next decade of circulating tumour cell research in lung cancer

Since blood borne circulating tumour cells (CTCs) initially shed from the primary tumour can seed and initiate metastasis at distant sites a better understanding of the biology of CTCs and their dissemination could provide valuable information that could guide therapeutic intervention and real time monitoring of disease progression. Although CTC enumeration has provided a reliable prognostic readout for a number of cancers, including lung cancer, the precise clinical utility of CTCs remains to be established. The rarity of CTCs together with the vanishingly small amounts of nucleic acids present in a single cell as well as cell to cell heterogeneity has stimulated the development of a wide range of powerful cellular and molecular methodologies applied to CTCs. These technical developments are now enabling researchers to focus on understanding the biology of CTCs and their clinical utility as a predictive and pharmacodynamics markers. This review summarises recent advances in the field of CTC research with focus on technical and biological challenges as well the progress made towards clinical utility of characterisation of CTCs with emphasis on studies in lung cancer.

METCAM/MUC18 promoted tumorigenesis of human breast cancer SK-BR-3 cells in a dosage-specific manner

OBJECTIVE

Overexpression of METCAM/MUC18, an immunoglobulin-like cell-adhesion molecule, promotes tumorigenesis and progression of human breast cancer cells. We also observed an intriguing phenomenon that a high-expressing SK-BR-3 clone manifested a transient tumor suppression effect in vivo. The purpose of this study was to understand if this was caused by clonal variation, METCAM/MUC18-dosage effect, or the number of cells injected.

MATERIALS AND METHODS

Several G418-resistant clones of SK-BR-3, expressing different levels of METCAM/MUC18, were obtained for testing effects of human METCAM/MUC18 on in vitro motility, invasiveness, and anchorage-independent colony formation (in vitro tumorigenicity) and in vivo tumorigenesis in female Balb/C athymic nude mice. Tumor sections were made for histology and immunohistochemistry analyses, and tumor lysates for Western blot analysis to determine the effects of human METCAM/MUC18 expression on levels of various downstream effectors.

RESULTS

METCAM/MUC18 promoted in vitro motility, invasiveness, and in vitro tumorigenicity of SK-BR-3 cells in a dosage-specific manner. Overexpression of METCAM/MUC18 could promote in vivo tumorigenesis of SK-BR-3 cells even when one tenth of the previously used cell number (5 × 10(5)) was injected and in vivo tumorigenesis of SK-BR-3 cells was directly proportional to the dosage of the protein. The previously observed transient tumor suppression effect from the same clone was no longer observed. The downstream effector, such as phospho-AKT/AKT ratio, was elevated in the tumors.

CONCLUSION

Transient suppression observed previously in the clone was caused by injection of a high cell number (2 × 10(6)-5 × 10(6)). METCAM/MUC18 positively promotes tumorigenesis of SK-BR-3 cells by increasing the survival and proliferation pathway.

PHOX2B is a suppressor of neuroblastoma metastasis

Paired like homeobox 2B (PHOX2B) is a minimal residual disease (MRD) marker of neuroblastoma. The presence of MRD, also referred to as micro-metastases, is a powerful marker of poor prognosis in neuroblastoma.

Lung metastasis is considered a terminal event in neuroblastoma. Lung micro-metastatic neuroblastoma (MicroNB) cells show high expression levels of PHOX2B and possess a less malignant and metastatic phenotype than lung macro metastatic neuroblastoma (MacroNB) cells, which hardly express PHOX2B.

In vitro assays showed that PHOX2B knockdown in MicroNB cells did not affect cell viability; however it decreased the migratory capacity of the MicroNB-shPHOX2B cells. An orthotopic inoculation of MicroNB-shPHOX2B cells into the adrenal gland of nude mice resulted in significantly larger primary tumors and a heavier micro-metastatic load in the lungs and bone-marrow, than when control cells were inoculated.

PHOX2B expression was found to be regulated by methylation. The PHOX2B promoter in MacroNB cells is significantly more methylated than in MicroNB cells. Demethylation assays using 5-azacytidine demonstrated that methylation can indeed inhibit PHOX2B transcription in MacroNB cells.

These pre-clinical data strongly suggest that PHOX2B functions as a suppressor of neuroblastoma progression.

FXR1a-associated microRNP: A driver of specialized non-canonical translation in quiescent conditions

Eukaryotic protein synthesis is a multifaceted process that requires coordination of a set of translation factors in a particular cellular state. During normal growth and proliferation, cells generally make their proteome via conventional translation that utilizes canonical translation factors. When faced with environmental stress such as growth factor deprivation, or in response to biological cues such as developmental signals, cells can reduce canonical translation. In this situation, cells adapt alternative modes of translation to make specific proteins necessary for required biological functions under these distinct conditions. To date, a number of alternative translation mechanisms have been reported, which include non-canonical, cap dependent translation and cap independent translation such as IRES mediated translation. Here, we discuss one of the alternative modes of translation mediated by a specialized microRNA complex, FXR1a-microRNP that promotes non-canonical, cap dependent translation in quiescent conditions, where canonical translation is reduced due to low mTOR activity.

Mathematical models of breast and ovarian cancers

Women constitute the majority of the aging United States (US) population, and this has substantial implications on cancer population patterns and management practices. Breast cancer is the most common women's malignancy, while ovarian cancer is the most fatal gynecological malignancy in the US. In this review, we focus on these subsets of women's cancers, seen more commonly in postmenopausal and elderly women. In order to systematically investigate the complexity of cancer progression and response to treatment in breast and ovarian malignancies, we assert that integrated mathematical modeling frameworks viewed from a systems biology perspective are needed. Such integrated frameworks could offer innovative contributions to the clinical women's cancers community, as answers to clinical questions cannot always be reached with contemporary clinical and experimental tools. Here, we recapitulate clinically known data regarding the progression and treatment of the breast and ovarian cancers. We compare and contrast the two malignancies whenever possible in order to emphasize areas where substantial contributions could be made by clinically inspired and validated mathematical modeling. We show how current paradigms in the mathematical oncology community focusing on the two malignancies do not make comprehensive use of, nor substantially reflect existing clinical data, and we highlight the modeling areas in most critical need of clinical data integration. We emphasize that the primary goal of any mathematical study of women's cancers should be to address clinically relevant questions. WIREs Syst Biol Med 2016, 8:337-362. doi: 10.1002/wsbm.1343 For further resources related to this article, please visit the WIREs website.

Investigating the Impact of a Primary Tumor on Metastasis and Dormancy Using MRI: New Insights into the Mechanism of Concomitant Tumor Resistance

Dormant cancer cells, also referred to as quiescent, slowly cycling or “nonproliferative” cells, are believed to contribute to tumor recurrence and present a therapeutic problem because they are nonresponsive to current therapies that target proliferating cells. Concomitant tumor resistance (CTR) is the ability of a primary tumor to restrict the growth of secondary metastases. In this paper, we investigate these 2 cancer concepts using cellular magnetic resonance imaging (MRI). A new model for CTR is presented where a primary mammary fat pad tumor is generated using a human breast cancer cell line (231) and breast cancer brain metastases are generated using a cell line derived from 231 to be brain metastatic (231-BR). Iron oxide particles are used to label the 231BR cells to allow for tracking of the proliferating cells, which form metastases, and the nonproliferating cells, which remain dormant in the brain. Bioluminescence and fluorescence-activated cell sorting are used to validate the MRI data. The presence of a primary 231 mammary fat pad tumor inhibited the formation of MRI-detectable 231BR brain metastases. More iron-retaining cells persisted in the brains of mice with a primary tumor. Bioluminescence and fluorescence-activated cell sorting provide evidence that signal voids detectable by MRI on day 0 represent live, iron-labeled cells in the brain. This work shows that retention of iron by nonproliferative cancer cells can be exploited to monitor the fate of this important cell population in vivo, and it points to a new mechanism for CTR, the enhancement of dormancy by a primary tumor.

Minimal residual disease in breast cancer: an overview of circulating and disseminated tumour cells

Within the field of cancer research, focus on the study of minimal residual disease (MRD) in the context of carcinoma has grown exponentially over the past several years. MRD encompasses circulating tumour cells (CTCs)—cancer cells on the move via the circulatory or lymphatic system, disseminated tumour cells (DTCs)—cancer cells which have escaped into a distant site (most studies have focused on bone marrow), and resistant cancer cells surviving therapy—be they local or distant, all of which may ultimately give rise to local relapse or overt metastasis. Initial studies simply recorded the presence and number of CTCs and DTCs; however recent advances are allowing assessment of the relationship between their persistence, patient prognosis and the biological properties of MRD, leading to a better understanding of the metastatic process. Technological developments for the isolation and analysis of circulating and disseminated tumour cells continue to emerge, creating new opportunities to monitor disease progression and perhaps alter disease outcome. This review outlines our knowledge to date on both measurement and categorisation of MRD in the form of CTCs and DTCs with respect to how this relates to cancer outcomes, and the hurdles and future of research into both CTCs and DTCs.

Intravital imaging of the effects of 5-fluorouracil on the murine liver microenvironment using 2-photon laser scanning microscopy

5-fluorouracil (5FU) is often used in the treatment of colorectal cancer. 5FU improves the median overall and disease-free survival rates and reduces recurrence rates in patients who have undergone curative surgical resection. However, in the adjuvant setting, whether 5FU eradicates clinically undetectable micrometastases in target organs such as the liver, or whether 5-FU inhibits the adhesion of circulating tumor cells has not yet been established. In the present study, 5FU was administered following the inoculation of red fluorescent protein-expressing HT29 cells into green fluorescent protein (GFP)-transgenic nude mice to examine its inhibitory effect. 2-photon laser scanning microscopy was performed at selected time points for time-series imaging of liver metastasis of GFP-transgenic mice. The cell number in vessels was quantified to evaluate the response of the tumor microenvironment to chemotherapy. HT29 cells were visualized in hepatic sinusoids at the single-cell level. A total of 2 hours after the injection (early stage), time-series imaging revealed that the number of caught tumor cells gradually reduced over time. In the 5FU treatment group, no significant difference was observed in the cell number in the early stage. One week after the injection (late stage), a difference in morphology was observed. The results of the present study indicated that 5FU eradicated clinically undetectable micrometastases in liver tissues by acting as a cytotoxic agent opposed to preventing adhesion. The present study indicated that time-series intravital 2-photon laser scanning microscopic imaging of metastatic tumor xenografts may facilitate the screening and evaluation of novel chemotherapeutic agents with less interindividual variability.

Annual Hazard Rates of Recurrence for Breast Cancer During 24 Years of Follow-Up: Results From the International Breast Cancer Study Group Trials I to V

PURPOSE

Predicting the pattern of recurrence can aid in the development of targeted surveillance and treatment strategies. We identified patient populations that remain at risk for an event at a median follow-up of 24 years from the diagnosis of operable breast cancer.

PATIENTS AND METHODS

International Breast Cancer Study Group clinical trials I to V randomly assigned 4,105 patients between 1978 and 1985. Annualized hazards were estimated for breast cancer-free interval (primary end point), disease-free survival, and overall survival.

RESULTS

For the entire group, the annualized hazard of recurrence was highest during the first 5 years (10.4%), with a peak between years 1 and 2 (15.2%). During the first 5 years, patients with estrogen receptor (ER)--positive disease had a lower annualized hazard compared with those with ER-negative disease (9.9% v 11.5%; P = .01). However, beyond 5 years, patients with ER-positive disease had higher hazards (5 to 10 years: 5.4% v 3.3%; 10 to 15 years: 2.9% v 1.3%; 15 to 20 years: 2.8% v 1.2%; and 20 to 25 years: 1.3% v 1.4%; P < .001). Among patients with ER-positive disease, annualized hazards of recurrence remained elevated and fairly stable beyond 10 years, even for those with no axillary involvement (2.0%, 2.1%, and 1.1% for years 10 to 15, 15 to 20, and 20 to 25, respectively) and for those with one to three positive nodes (3.0%, 3.5%, and 1.5%, respectively).

CONCLUSION

Patients with ER-positive breast cancer maintain a significant recurrence rate during extended follow up. Strategies for follow up and treatments to prevent recurrences may be most efficiently applied and studied in patients with ER-positive disease followed for a long period of time.

Cancer Metastases: Early Dissemination and Late Recurrences

BACKGROUND

Metastatic cells from a primary tumor can occur before the primary cancer is detected. Metastatic cells can also remain in the patient for many years after removal of the primary tumor without proliferating. These dormant malignant cells can awaken and cause recurrent disease decades after the primary treatment. The purpose of this article is to review the clinical evidence for early dissemination and late recurrences in human malignant tumors. We used the following definitions: dormancy of cells may be defined as a nonproliferating state or an arrest in the cell cycle that results in a prolonged G0 phase. If one accepts the term "late metastases" to indicate a period exceeding 10 years from the removal of the primary tumor, then the two malignancies in which this occurs most frequently are cutaneous malignant melanoma (CMM) and renal cell carcinoma (RCC).

METHODS

PubMed, Web of Science, and Scopus were searched with the keywords "metastases," "early dissemination," "late recurrences," "inadvertently transmitted cancer," "tumor growth rate," "dormancy," "circulating tumor cells," and "transplantation of cancer."

RESULTS

Several case reports of early dissemination and late recurrences of various types of malignancies were found. Analyses of the growth rates of several malignant tumors in the original host indicated that the majority of cancers had metastasized years before they were detected. CMM, RCC, and malignant glioblastoma were the three most common malignancies resulting from an organ transplantation. CMM and RCC were also the two most common malignancies that showed dormancy. In several cases of transplanted CMM and RCC, the donor did not have any known malignancy or had had the malignancy removed so long ago that the donor was regarded as cured.

CONCLUSION

(1) Metastases can frequently exist prior to the detection of the primary tumor. (2) Metastatic cells may reside in organs in the original host that are not usually the site of detectable secondary tumors, for example, the kidneys and heart. (3) Metastatic cells remain dormant for decades after the primary tumor has been removed. (4) Dormancy might be reversible and lead to late recurrences.

Biology, detection, and clinical implications of circulating tumor cells

Cancer metastasis is the main cause of cancer-related death, and dissemination of tumor cells through the blood circulation is an important intermediate step that also exemplifies the switch from localized to systemic disease. Early detection and characterization of circulating tumor cells (CTCs) is therefore important as a general strategy to monitor and prevent the development of overt metastatic disease. Furthermore, sequential analysis of CTCs can provide clinically relevant information on the effectiveness and progression of systemic therapies (e.g., chemo-, hormonal, or targeted therapies with antibodies or small inhibitors). Although many advances have been made regarding the detection and molecular characterization of CTCs, several challenges still exist that limit the current use of this important diagnostic approach. In this review, we discuss the biology of tumor cell dissemination, technical advances, as well as the challenges and potential clinical implications of CTC detection and characterization.

Investigating breast cancer cell behavior using tissue engineering scaffolds

Despite early detection through the use of mammograms and aggressive intervention, breast cancer (BC) remains a clinical dilemma. BC can resurge after >10 years of remission. Studies indicate that BC cells (BCCs) with self-renewal and chemoresistance could be involved in dormancy. The majority of studies use in vitro, two-dimensional (2-D) monolayer cultures, which do not recapitulate the in vivo microenvironment. Thus, to determine the effect of three-dimensional (3-D) microenvironment on BCCs, this study fabricated tissue engineering scaffolds made of poly (ε-caprolactone) (PCL) having aligned or random fibers. Random and aligned fibers mimic, respectively, the random and highly organized collagen fibers found in the tumor extracellular matrix. Chemoresistant BCCs were obtained by treating with carboplatin. Western blot analysis of carboplatin resistant (treated) MDA-MB-231 (highly invasive, basal-like) and T47D (low-invasive, luminal) BCCs showed an increase in Bcl-2, Oct-4 and Sox-2, suggesting protection from apoptosis and increase in stem-like markers. Further studies with MDA-MB-231 BCCs seeded on the scaffolds showed little to no change in cell number over time for non-treated BCCs whereas on tissue culture polystyrene (TCP), non-treated BCCs displayed a significant increase in cell number at days 4 and 7 as compared to day 1 (p<0.05). Treated BCCs did not proliferate on TCP and the fibrous scaffolds. Little to no cyclin D1 was expressed for non-treated BCCs on TCP. On fibrous scaffolds, non-treated BCCs stained for cyclin D1 during the 7-day culture period. Treated BCCs expressed cyclin D1 on TCP and fibrous scaffolds during the 7-day culture period. Proliferation, viability and cell cycle analysis indicated that this 3-D culture prompted the aggressive BCCs to adopt a dormant phenotype, while the treated BCCs retained their phenotype. The findings indicate that random and aligned fibrous PCL scaffolds may provide a useful system to study how the 3-D microenvironment affects the behavior of BCCs.

Leukocytes as carriers for targeted cancer drug delivery

INTRODUCTION

Metastasis contributes to over 90% of cancer-related deaths. Numerous nanoparticle platforms have been developed to target and treat cancer, yet efficient delivery of these systems to the appropriate site remains challenging. Leukocytes, which share similarities to tumor cells in terms of their transport and migration through the body, are well suited to serve as carriers of drug delivery systems to target cancer sites.

AREAS COVERED

This review focuses on the use and functionalization of leukocytes for therapeutic targeting of metastatic cancer. Tumor cell and leukocyte extravasation, margination in the bloodstream, and migration into soft tissue are discussed, along with the potential to exploit these functional similarities to effectively deliver drugs. Current nanoparticle-based drug formulations for the treatment of cancer are reviewed, along with methods to functionalize delivery vehicles to leukocytes, either on the surface and/or within the cell. Recent progress in this area, both in vitro and in vivo, is also discussed, with a particular emphasis on targeting cancer cells in the bloodstream as a means to interrupt the metastatic process.

EXPERT OPINION

Leukocytes interact with cancer cells both in the bloodstream and at the site of solid tumors. These interactions can be utilized to effectively deliver drugs to targeted areas, which can reduce both the amount of drug required and various nonspecific cytotoxic effects within the body. If drug delivery vehicle functionalization does not interfere with leukocyte function, this approach may be utilized to neutralize tumor cells in the bloodstream to prevent the formation of new metastases, and also to deliver drugs to metastatic sites within tissues.

Suppression of early hematogenous dissemination of human breast cancer cells to bone marrow by retinoic Acid-induced 2

Regulatory pathways that drive early hematogenous dissemination of tumor cells are insufficiently defined. Here, we used the presence of disseminated tumor cells (DTC) in the bone marrow to define patients with early disseminated breast cancer and identified low retinoic acid-induced 2 (RAI2) expression to be significantly associated with DTC status. Low RAI2 expression was also shown to be an independent poor prognostic factor in 10 different cancer datasets. Depletion of RAI2 protein in luminal breast cancer cell lines resulted in dedifferentiation marked by downregulation of ERα, FOXA1, and GATA3, together with increased invasiveness and activation of AKT signaling. Functional analysis of the previously uncharacterized RAI2 protein revealed molecular interaction with CtBP transcriptional regulators and an overlapping function in controlling the expression of a number of key target genes involved in breast cancer. These results suggest that RAI2 is a new metastasis-associated protein that sustains differentiation of luminal breast epithelial cells.

SIGNIFICANCE

We identified downregulation of RAI2 as a novel metastasis-associated genetic alteration especially associated with early occurring bone metastasis in ERα-positive breast tumors. We specified the role of the RAI2 protein to function as a transcriptional regulator that controls the expression of several key regulators of breast epithelial integrity and cancer.

Identification of genomic signatures in circulating tumor cells from breast cancer

Levels of circulating tumor cells (CTCs) in blood have prognostic value in early and metastatic breast cancer. CTCs also show varying degrees of concordance with molecular markers of primary tumors they originate from. It is expected that individual cells reflect the heterogeneity and evolution of tumor cells as they acquire new functions and differential responses to chemotherapy. However, a degree of commonality is also plausible, highlighting alterations that allow tumor cells to perform CTC-defining activities such as invasion and intravasation. Using a matched tumor-normal approach, we performed high-resolution copy number profiling of CTCs from breast cancer to identify occult changes occurring during progression to metastasis. We identified a signature of recurrent gain in CTCs, consisting of 90 minimal common regions (MCRs) of copy number gain. These were predominantly found across chromosome 19 and were identified at low frequencies (3-4%) in 787 primary breast carcinomas examined. CTC genomic signatures clustered into two groups independent of subtype: a dormancy-related signature with 16 MCRs (AKT2, PTEN, CADM2); and a tumor-aggressiveness related signature with 358 MCRs (ANGPTL4, BSG, MIR-373). There were two MCRs in common between the groups on 19q13 and 21q21, containing genes involved in resistance to anoikis, TGFβ-signaling and metastasis (TFF3, LTBP4, NUMBL). Furthermore, a region harboring the ERBB2 gene was gained in a majority of patients. Regions 20q13 and 15q24 were associated with distant metastasis. The distinctiveness of CTC signatures highlights cell populations with different functional or metastatic potential. Such novel targets could help to specifically identify and block dissemination.

The host microenvironment influences prostate cancer invasion, systemic spread, bone colonization, and osteoblastic metastasis

Prostate cancer (PCa) is the second leading cause of cancer death in men worldwide. Most PCa deaths are due to osteoblastic bone metastases. What triggers PCa metastasis to the bone and what causes osteoblastic lesions remain unanswered. A major contributor to PCa metastasis is the host microenvironment. Here, we address how the primary tumor microenvironment influences PCa metastasis via integrins, extracellular proteases, and transient epithelia-mesenchymal transition (EMT) to promote PCa progression, invasion, and metastasis. We discuss how the bone-microenvironment influences metastasis; where chemotactic cytokines favor bone homing, adhesion molecules promote colonization, and bone-derived signals induce osteoblastic lesions. Animal models that fully recapitulate human PCa progression from primary tumor to bone metastasis are needed to understand the PCa pathophysiology that leads to bone metastasis. Better delineation of the specific processes involved in PCa bone metastasize is needed to prevent or treat metastatic PCa. Therapeutic regimens that focus on the tumor microenvironment could add to the PCa pharmacopeia.

Perforin-dependent direct cytotoxicity in natural killer cells induces considerable knockdown of spontaneous lung metastases and computer modelling-proven tumor cell dormancy in a HT29 human colon cancer xenograft mouse model

BACKGROUND

For long, natural killer (NK) cells have been suspected to play a critical role in suppressing the development of spontaneous metastases in cancer patients. Despite a wide range of studies it remains unclear so far to what extent primary tumor growth together with formation of distant metastases and NK cell activity influence each other.

METHODS

To precisely investigate the role of NK cells with a perforin-deficiency in cancer growth and metastasis formation, human HT29 colon cancer cells were subcutaneously grafted into pore forming protein and recombination activating gene 2 double knock out (pfp/rag2) mice and in recombination activating gene 2 only knock out (rag2) mice both with black six background. Both mice lack B and T cell functions due to the absence of rag2.

RESULTS

Primary tumors developed in 16/16 in pfp/rag2 and 20/20 rag2 mice. At sacrifice primary tumor weight did not differ significantly. However, tumors grew faster in pfp/rag2 mice (50 days) than in pfp/rag2 mice (70 days). Circulating tumor cells (CTC) in murine blood were nearly three times higher in pfp/rag2 (68 cells/ml) than in rag2 mice (24 cells/ml). Lung metastases occurred frequently in pfp/rag2 mice (13/16) and infrequently in rag2 mice (5/20). The mean number of metastases was 789 in pfp/rag2 mice compared to 210 in rag2 mice. Lung metastases in pfp/rag2 mice consisted of 10-100 tumor cells while those in rag2 mice were generally disseminated tumor cells (DTCs).Computer modelling showed that perforin-dependent killing of NK cells decelerates the growth of the primary tumour and kills 80% of CTCs. Furthermore, perforin-mediated cytotoxicity hampers the proliferation of the malignant cells in host tissue forcing them to stay dormant for at least 30 days.

CONCLUSION

The results exactly quantified the effect of perforin-dependent direct cytotoxicity of NK cells on HT29 on primary tumor growth, number of CTCs in the blood and the number of metastases. The largest effects were seen in the number of mice developing spontaneous lung metastases and the mean number of lung metastases. Hence, perforin-mediated cytotoxicity used for direct killing by NK cells is more important than indirect killing by secretion of death-inducing ligands by NK cells.

Prognostic relevance of minimal residual disease in colorectal cancer

Presence of occult minimal residual disease in patients with colorectal cancer (CRC) has a strong prognostic impact on survival. Minimal residual disease plays a major role in disease relapse and formation of metastases in CRC. Analysis of circulating tumor cells (CTC) in the blood is increasingly used in clinical practice for disease monitoring of CRC patients. In this review article the role of CTC, disseminated tumor cells (DTC) in the bone marrow and micrometastases and isolated tumor cells (ITC) in the lymph nodes will be discussed, including literature published until September 2013. Occult disease is a strong prognostic marker for patient survival in CRC and defined by the presence of CTC in the blood, DTC in the bone marrow and/or micrometastases and ITC in the lymph nodes. Minimal residual disease could be used in the future to identify patient groups at risk, who might benefit from individualized treatment options.

Prognostic value of bone marrow micrometastasis in patients with operable esophageal squamous cell carcinoma: a long-term follow-up study

INTRODUCTION

Detection of bone marrow micrometastasis (BMM) has been focused on as a prognostic parameter in various malignant neoplasms recently. This study was designed to evaluate the prognostic significance of BMM detection in patients with operable esophageal squamous cell carcinoma (ESCC) after long-term follow-up.

METHODS

In 61 consecutive patients with ESCC who had undergone radical surgical resection, BMM was detected through reverse transcriptase-polymerase chain reaction (RT-PCR). Correlation between BMM detection and prognosis of the 61 patients was analyzed.

RESULTS

BMM was found in 13 patients (21.3%). No significant correlation between BMM detection and tumor, node, metastasis (TNM) stage was found. The median survival time, 5-year overall survival rate, 5-year disease-free survival rate, and 5-year distant disease-free survival rate for cases with positive BMM were 13.0 months, 15.4%, 7.7%, and 34.2%, respectively, compared with that of 66.0 months, 59.7%, 49.1%, and 60.6% for cases with negative BMM (p < 0.05). In multivariate analysis, BMM were found to be an independent factor in the prediction of overall survival (odds ratio [OR] 3.928, p = 0.001), disease-free survival (OR 4.285, p < 0.001), and distant disease-free survival (OR 3.270, p = 0.013).

CONCLUSIONS

BMM is an independent prognostic factor in the prediction of the subsequent development of metastatic disease and disease outcome for operable ESCC patients, and may be a useful adjunct to conventional tumor staging. Further studies are required to evaluate the value of neoadjuvant or adjuvant systemic therapy in ESCC patients with BMM.