Increased expression and serum levels of the stromal cell-secreted protein periostin in breast cancer bone metastases

The molecular signature of the stroma response in prostate cancer-induced osteoblastic bone metastasis highlights expansion of hematopoietic and prostate epithelial stem cell niches

The reciprocal interaction between cancer cells and the tissue-specific stroma is critical for primary and metastatic tumor growth progression. Prostate cancer cells colonize preferentially bone (osteotropism), where they alter the physiological balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption, and elicit prevalently an osteoblastic response (osteoinduction). The molecular cues provided by osteoblasts for the survival and growth of bone metastatic prostate cancer cells are largely unknown. We exploited the sufficient divergence between human and mouse RNA sequences together with redefinition of highly species-specific gene arrays by computer-aided and experimental exclusion of cross-hybridizing oligonucleotide probes. This strategy allowed the dissection of the stroma (mouse) from the cancer cell (human) transcriptome in bone metastasis xenograft models of human osteoinductive prostate cancer cells (VCaP and C4-2B). As a result, we generated the osteoblastic bone metastasis-associated stroma transcriptome (OB-BMST). Subtraction of genes shared by inflammation, wound healing and desmoplastic responses, and by the tissue type-independent stroma responses to a variety of non-osteotropic and osteotropic primary cancers generated a curated gene signature ("Core" OB-BMST) putatively representing the bone marrow/bone-specific stroma response to prostate cancer-induced, osteoblastic bone metastasis. The expression pattern of three representative Core OB-BMST genes (PTN, EPHA3 and FSCN1) seems to confirm the bone specificity of this response. A robust induction of genes involved in osteogenesis and angiogenesis dominates both the OB-BMST and Core OB-BMST. This translates in an amplification of hematopoietic and, remarkably, prostate epithelial stem cell niche components that may function as a self-reinforcing bone metastatic niche providing a growth support specific for osteoinductive prostate cancer cells. The induction of this combinatorial stem cell niche is a novel mechanism that may also explain cancer cell osteotropism and local interference with hematopoiesis (myelophthisis). Accordingly, these stem cell niche components may represent innovative therapeutic targets and/or serum biomarkers in osteoblastic bone metastasis.

A signature of epithelial-mesenchymal plasticity and stromal activation in primary tumor modulates late recurrence in breast cancer independent of disease subtype

Introduction

Despite improvements in adjuvant therapy, late systemic recurrences remain a lethal consequence of both early- and late-stage breast cancer. A delayed recurrence is thought to arise from a state of tumor dormancy, but the mechanisms that govern tumor dormancy remain poorly understood.

Methods

To address the features of breast tumors associated with late recurrence, but not confounded by variations in systemic treatment, we compiled breast tumor gene expression data from 4,767 patients and established a discovery cohort consisting of 743 lymph node-negative patients who did not receive systemic neoadjuvant or adjuvant therapy. We interrogated the gene expression profiles of the 743 tumors and identified gene expression patterns that were associated with early and late disease recurrence among these patients. We applied this classification to a subset of 46 patients for whom expression data from microdissected tumor epithelium and stroma was available, and identified a distinct gene signature in the stroma and also a corresponding tumor epithelium signature that predicted disease recurrence in the discovery cohort. This tumor epithelium signature was then validated as a predictor for late disease recurrence in the entire cohort of 4,767 patients.

Results

We identified a novel 51-gene signature from microdissected tumor epithelium associated with late disease recurrence in breast cancer independent of the molecular disease subtype. This signature correlated with gene expression alterations in the adjacent tumor stroma and describes a process of epithelial to mesenchymal transition (EMT) and tumor-stroma interactions.

Conclusions

Our findings suggest that an EMT-related gene signature in the tumor epithelium is related to both stromal activation and escape from disease dormancy in breast cancer. The presence of a late recurrence gene signature in the primary tumor also suggests that intrinsic features of this tumor regulate the transition of disseminated tumor cells into a dormant phenotype with the ability to outgrowth as recurrent disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0407-9) contains supplementary material, which is available to authorized users.

Serum periostin is associated with fracture risk in postmenopausal women: a 7-year prospective analysis of the OFELY study

PURPOSE

Periostin (POSTN) is a secreted γ-carboxyglutamic acid-containing protein expressed mainly in the periosteum in adult individuals. POSNT deficient mice develop periodontis and osteoporosis with decreased bone strength. The relationship between serum POSTN and bone metabolism and fracture risk in postmenopausal women is unknown.

SUBJECTS AND METHODS

Serum POSTN was measured in 607 postmenopausal women (mean age 66.6 ± 8.4 y) from the Os des Femmes de Lyon cohort at the ninth annual follow-up visit (baseline visit of the current analysis). Nonvertebral and clinical vertebral incident fragility fractures were reported annually during 7 years. Areal bone mineral density (BMD; measured by dual energy X-ray absorptiometry) of the hip and bone markers (intact N-terminal propeptide of type I collagen, osteocalcin, and serum type I collagen C-telopeptide) were also measured.

RESULTS

At baseline, serum POSTN did not correlate with age, bone markers, and BMD. After a median of 7 years of follow-up, 75 women sustained an incident clinical vertebral or nonvertebral fragility fracture. The proportion of women who had an incident fracture was significantly higher in women with levels of POSTN in the highest quartile than that of women in the three other quartiles (19.5% vs 10.1%, P = .018) after adjustment for age and prevalent fracture. The highest quartile of POSTN was associated with an increased risk of incident fracture with a relative risk (95% confidence interval) of 1.88 (1.1-3.2) after adjustment for age, prevalent fracture, and hip BMD T-score. Patients with both low hip BMD (T-score < -2.5) and high levels of POSTN (fourth quartile) had a relative risk of fracture of 7.1 (95% confidence interval 2.4-21.8) after adjustment for age.

CONCLUSION

High serum POSTN levels are independently associated with increased fracture risk in postmenopausal women. These data suggest that serum POSTN could be useful to improve fracture risk assessment.

Integrated extracellular matrix signaling in mammary gland development and breast cancer progression

Extracellular matrix (ECM), a major component of the cellular microenvironment, plays critical roles in normal tissue morphogenesis and disease progression. Binding of ECM to membrane receptor proteins, such as integrin, discoidin domain receptors, and dystroglycan, elicits biochemical and biomechanical signals that control cellular architecture and gene expression. These ECM signals cooperate with growth factors and hormones to regulate cell migration, differentiation, and transformation. ECM signaling is tightly regulated during normal mammary gland development. Deposition and alignment of fibrillar collagens direct migration and invasion of mammary epithelial cells during branching morphogenesis. Basement membrane proteins are required for polarized acinar morphogenesis and milk protein expression. Deregulation of ECM proteins in the long run is sufficient to promote breast cancer development and progression. Recent studies demonstrate that the integrated biophysical and biochemical signals from ECM and soluble factors are crucial for normal mammary gland development as well as breast cancer progression.

The niche component periostin is produced by cancer-associated fibroblasts, supporting growth of gastric cancer through ERK activation

Overexpression of periostin (POSTN), an extracellular matrix protein, has been observed in several cancers. We investigated the importance of POSTN in gastric cancer. Genome-wide gene expression analysis using publicly available microarray data sets revealed significantly high POSTN expression in cancer tissues from stage II-IV gastric cancer, compared with background normal tissues. The POSTN/vimentin mRNA expression ratio was highly associated with gene groups that regulate the cell cycle and cell proliferation. IHC showed that periglandular POSTN deposition, comprising linear deposition abutting the glandular epithelial cells in normal mucosa, disappeared during intestinal gastric cancer progression. Stromal POSTN deposition was also detected at the invasive front of intestinal-type and diffuse-type cancers. In situ hybridization confirmed POSTN mRNA in cancer-associated fibroblasts, but not in tumor cells themselves. POSTN enhanced the in vitro growth of OCUM-2MLN and OCUM-12 diffuse-type gastric cancer cell lines, accompanied by the activation of ERK. Furthermore, coinoculation of gastric cancer cells with POSTN-expressing NIH3T3 mouse fibroblast cells facilitated tumor formation. The OCUM-2MLN orthotopic inoculation model demonstrated that tumors of the gastric wall in Postn(-/-) mice were significantly smaller than those in wild-type mice. Ki-67 and p-ERK positive rates were both lower in Postn(-/-) mice. These findings suggest that POSTN produced by cancer-associated fibroblasts constitutes a growth-supportive microenvironment for gastric cancer.

Periostin contributes to the acquisition of multipotent stem cell-like properties in human mammary epithelial cells and breast cancer cells

Periostin (POSTN), a recently characterised matricellular protein, is frequently dysregulated in various malignant cancers and promotes tumor metastatic growth. POSTN plays a critical role in the crosstalk between murine breast cancer stem cells (CSCs) and their niche to permit metastatic colonization. However, whether pro-metastatic capability of POSTN is associated with multipotent potentials of mesenchymal stem cells (MSCs) has not been documented. Here we demonstrate that POSTN promotes a stem cell-like trait and a mesenchymal phenotype in human mammary epithelial cells and breast cancer cells. Interestingly, ectopic overexpression of POSTN or recombinant POSTN treatment can induce human mammary epithelial cells and breast cancer cells differentiation into multiple cell lineages that recapitulate part of the multilineage differentiation potentials of MSCs. Moreover, POSTN is highly expressed in bone marrow-derived MSCs and their derived adipocytes, chondrocytes, and osteoblasts in vitro. Furthermore, POSTN promotes the growth of xenograft tumors in vivo. POSTN-overexpressing human mammary epithelial cells enhance breast tumor growth and metastasis. These data thus provide evidence of a new role for POSTN in mammary epithelial neoplasia and metastasis, suggesting that epithelial cancer cells might acquire CSC-like traits and a mesenchymal phenotype, as well as the multipotent potentials of MSCs to promote tumorigenesis and metastasis. Therefore, targeting POSTN and other extracellular matrix components of tumor microenvironment may help to develop new therapeutical strategies to inhibit tumor metastasis.

High preoparative levels of serum periostin are associated with poor prognosis in patients with hepatocellular carcinoma after hepatectomy

AIMS

Periostin (POSTN) is implicated in cancer development and progression. The aim of this study was to evaluate the diagnostic and prognostic significance of serum POSTN in patients with hepatocellular carcinoma (HCC) receiving curative surgery.

METHODS

Enzyme-linked immunosorbent assay was performed to determine serum POSTN levels in 69 healthy volunteers, 30 patients with hepatolithiasis, 27 patients with cirrhosis, and 56 HCC patients. The relationships between serum POSTN and clinicopathologic features were analyzed. Receiver operating characteristics analysis was used to calculate diagnostic accuracy of serum POSTN, serum alpha-fetoprotein (AFP), and their combination. The prognostic impact of serum POSTN on overall survival (OS) and relapse-free survival (RFS) was also investigated.

RESULTS

The median serum POSTN level was significantly (P < 0.05) increased in HCC patients, compared to healthy controls, patients with hepatolithiasis, and patients with liver cirrhosis. Elevated serum POSTN was only significantly associated with Edmondson grade (P = 0.007). The combination of serum POSTN and AFP had a markedly higher area under the curve (0.805 (95% confidence interval [CI]: 0.677-0.932)) than POSTN (0.582 (95% CI: 0.427-0.736)) or AFP (0.655 (95% CI: 0.504-0.806)) alone. Kaplan-Meier analysis indicated that elevated serum POSTN was associated with OS (P = 0.031) and RFS (P = 0.027). Moreover, multivariate analysis revealed elevated serum POSTN as an independent poor prognostic marker for OS and RFS.

CONCLUSIONS

Preoperative serum POSTN has limited diagnostic value in distinguishing HCC from non-malignant liver diseases, but serves as independent prognostic biomarker in HCC patients.

Clear cell renal cell carcinoma induces fibroblast-mediated production of stromal periostin

OBJECTIVES

Increase in periostin (PN) was reported in clear cell renal cell carcinoma (ccRCC). But how PN contributes to ccRCC pathogenesis remains unclear. This research will investigate the underlying mechanism.

METHODS

The PN protein in 37 adjacent non-tumour kidney (ANK) tissues, their respective ccRCCs, 16 cases of metastasised ccRCC and xenograft tumours was analysed by immunohistochemistry. PN expression in ccRCC cells and NIH3T3 fibroblasts was examined by real time PCR (polymerase chain reaction) and western blot.

RESULTS

PN was detected at low levels in the tubular epithelial cells of ANKs. PN was robustly increased in the ccRCC-associated stroma of both organ-confined and metastasised ccRCCs. Furthermore, despite A498 ccRCC cells and their-derived xenograft tumour cells expressing a low level of PN, a strong presence of stromal PN was observed especially in the boundary region between xenograft tumour mass and non-tumour tissue. Collectively, these results suggest that the ccRCC-associated PN was derived from stroma instead of tumours. This notion was supported by the co-existence of PN with α-smooth muscle actin (αSMA), a marker of activated fibroblasts, in both local and metastasised ccRCC. Furthermore, co-culture of NIH3T3 mouse fibroblasts with either human A498 or 786-0 ccRCC cells dramatically enhanced PN transcription only in NIH3T3 cells as well as NIH3T3 cell-mediated accumulation of extracellular PN. In return, extracellular PN significantly enhanced A498 cell attachment. Elevation of PN promotes NIH3T3 cell proliferation and enhanced AKT activation.

CONCLUSIONS

ccRCC induces fibroblast-mediated accumulation of stromal PN; stromal PN enhances ccRCC cell attachment and fibroblast proliferation.

Periostin-binding DNA aptamer inhibits breast cancer growth and metastasis

Periostin is an extracellular matrix (ECM) protein that is overexpressed in a variety of human cancers, and its functions appear to be linked to tumor growth, metastasis, and angiogenesis. Recent clinical evidence suggests that aberrant periostin expression is correlated with poor outcome in patients with breast cancer. To identify novel tools to regulate the functional role of periostin, we generated benzyl-d(U)TP-modified DNA aptamers that were directed against human periostin (PNDAs) and characterized their functional roles in breast cancer progression. PNDA-3 selectively bound to the FAS-1 domain of periostin with nanomolar affinity and disrupted the interaction between periostin and its cell surface receptors, αvβ3 and αvβ5 integrins. PNDA-3 markedly antagonized the periostin-induced adhesion, migration, and invasion of breast cancer cells and blocked the activation of various components of the αvβ3 and αvβ5 integrin signal transduction pathways. In a 4T1 orthotopic mouse model, PNDA-3 administration significantly reduced primary tumor growth and distant metastasis. Thus, our results demonstrated that periostin-integrin signaling regulates breast cancer progression at multiple levels in tumor cells and the tumor microenvironment. DNA aptamers targeting periostin may potentially be used to inhibit breast cancer progression.

Clinical implications of periostin in the liver metastasis of colorectal cancer

AIM

To investigate the expression status of periostin in colorectal cancer (CRC) to lay a foundation for managing this disease.

METHODS

Periostin expression status was detected by immunohistochemistry staining in 720 CRC specimens. The relationship between the periostin protein and clinicopathological factors and prognosis was subsequently determined.

RESULT

The periostin protein was expressed significantly higher in CD133+ tumor cells compared to CD133- tumor cells. Positively expressed periostin was observed in 218 (30.28%) of the 720 cases. Spearman correlation analysis showed that periostin expression has a linear correlation to the tumor size, histological type, lymph node metastasis, TNM stage, and postoperative liver metastasis (p=0.02, 0.035, 0.001, 0.001, and 0.001, respectively). Multivariate analysis showed that histological type, lymph node metastasis, TNM stage, and periostin were found to be related to liver metastasis (p=0.01, 0.035, 0.01, and 0.001, respectively). In the Cox regression test, the histological grade, Lymph node metastasis, TNM stage, and periostin were detected as independent prognostic factors (p=0.01, 0.001, 0.001, and 0.001, respectively).

CONCLUSION

Periostin was found to be related to the liver metastasis of CRC and may be a potential target for CRC.

Cancer stem cell-related gene periostin: a novel prognostic marker for breast cancer

We investigated the expression status of periostin in breast cancer stem cells and its clinical implications in order to lay a foundation for managing breast cancer. CD44+/CD24−/line- tumor cells (CSC) from clinical specimens were sorted using flow cytometry. Periostin expression status was detected in CSC cells and 1,086 breast cancer specimens by Western blot and immunohistochemistry staining, with the CSC ratio determined by immunofluorescence double staining. The relationship between the periostin protein and clinico-pathological parameters and prognosis was subsequently determined. As a result, CSC cells are more likely to generate new tumors in mice and cell microspheres that are deficient in NOD/SCID compared to the control group. Periostin protein was expressed higher in CSC cells compared to the control cells and was found to be related to CSC chemotherapy resistance. Moreover, periostin expression was found to be related to the CSC ratio in 1,086 breast cancer specimens (P = 0.001). In total, 334 (30.76%) of the 1,086 breast cases showed high periostin expression. After universal and Spearman regression correlation analysis, periostin was observed to be related to histological grade, CSC ratio, lymph node metastasis, tumor size, and triple-negative breast cancer (all P<0.05). Furthermore, periostin was shown to attain a significantly more distant bone metastasis and worse disease-specific survival than those with none or low-expressed periostin protein (P = 0.001). In the Cox regression test, periostin protein was detected as an independent prognostic factor (P = 0.001). In conclusion, periostin was found to be related to the CSC and an independent prognostic factor for breast cancer. It is also perhaps a potential target to breast cancer.

Lysophosphatidic acid-induced ADAM12 expression mediates human adipose tissue-derived mesenchymal stem cell-stimulated tumor growth

Lysophosphatidic acid (LPA) is involved in mesenchymal stem cell-stimulated tumor growth in vivo. However, the molecular mechanism by which mesenchymal stem cells promote tumorigenesis remains elusive. In the present study, we demonstrate that conditioned medium from A549 human lung adenocarcinoma cells (A549 CM) induced the expression of ADAM12, a disintegrin and metalloproteases family member, in human adipose tissue-derived mesenchymal stem cells (hASCs). A549 CM-stimulated ADAM12 expression was abrogated by pretreatment of hASCs with the LPA receptor 1 inhibitor Ki16425 or by small interfering RNA-mediated silencing of LPA receptor 1, suggesting a key role for the LPA-LPA receptor 1 signaling axis in A549 CM-stimulated ADAM12 expression. Silencing of ADAM12 expression using small interfering RNA or short hairpin RNA abrogated LPA-induced expression of both α-smooth muscle actin, a marker of carcinoma-associated fibroblasts, and ADAM12 in hASCs. Using a xenograft transplantation model of A549 cells, we demonstrated that silencing of ADAM12 inhibited the hASC-stimulated in vivo growth of A549 xenograft tumors and the differentiation of transplanted hASCs to α-smooth muscle actin-positive carcinoma-associated fibroblasts. LPA-conditioned medium from hASCs induced the adhesion of A549 cells and silencing of ADAM12 inhibited LPA-induced expression of extracellular matrix proteins, periostin and βig-h3, in hASCs and LPA-conditioned medium-stimulated adhesion of A549 cells. These results suggest a pivotal role for LPA-stimulated ADAM12 expression in tumor growth and the differentiation of hASCs to carcinoma-associated fibroblasts expressing α-smooth muscle actin, periostin, and βig-h3.

The multiple facets of periostin in bone metabolism

Periostin is a matricellular glutamate-containing protein expressed during ontogenesis and in adult connective tissues submitted to mechanical strains including bone and, more specifically, the periosteum, periodontal ligaments, tendons, heart valves, or skin. It is also expressed in neoplastic tissues, cardiovascular and fibrotic diseases, and during wound repair. Its biological functions are extensively investigated in fields such as cardiovascular physiology or oncology. Despite its initial identification in bone, investigations of periostin functions in bone-related physiopathology are less abundant. Recently, several studies have analyzed the potential role of periostin in bone biology and suggest that periostin may be an important regulator of bone formation. The aim of this article is to provide an extensive review on the implications of periostin in bone biology and its potential use in benign and metabolic bone diseases.

Characterization and clinical evaluation of CD10+ stroma cells in the breast cancer microenvironment

PURPOSE

There is growing evidence that interaction between stromal and tumor cells is pivotal in breast cancer progression and response to therapy. Based on earlier research suggesting that during breast cancer progression, striking changes occur in CD10(+) stromal cells, we aimed to better characterize this cell population and its clinical relevance.

EXPERIMENTAL DESIGN

We developed a CD10(+) stroma gene expression signature (using HG U133 Plus 2.0) on the basis of the comparison of CD10 cells isolated from tumoral (n = 28) and normal (n = 3) breast tissue. We further characterized the CD10(+) cells by coculture experiments of representative breast cancer cell lines with the different CD10(+) stromal cell types (fibroblasts, myoepithelial, and mesenchymal stem cells). We then evaluated its clinical relevance in terms of in situ to invasive progression, invasive breast cancer prognosis, and prediction of efficacy of chemotherapy using publicly available data sets.

RESULTS

This 12-gene CD10(+) stroma signature includes, among others, genes involved in matrix remodeling (MMP11, MMP13, and COL10A1) and genes related to osteoblast differentiation (periostin). The coculture experiments showed that all 3 CD10(+) cell types contribute to the CD10(+) stroma signature, although mesenchymal stem cells have the highest CD10(+) stroma signature score. Of interest, this signature showed an important role in differentiating in situ from invasive breast cancer, in prognosis of the HER2(+) subpopulation of breast cancer only, and potentially in nonresponse to chemotherapy for those patients.

CONCLUSIONS

Our results highlight the importance of CD10(+) cells in breast cancer prognosis and efficacy of chemotherapy, particularly within the HER2(+) breast cancer disease.

Periostin: a promising target of therapeutical intervention for prostate cancer

Background

In our recent study, Periostin was up-regulated in prostate cancer(PCa) compared with benign prostate hyperplasia (BPH) by proteomics analysis of prostate biopsies. We investigated the effect of sliencing Periostin by RNA interference (RNAi) on the proliferation and migration of PCa LNCap cell line.

Methods

All the prostate biopsies from PCa, BPH and BPH with local prostatic intraepithelial neoplasm(PIN) were analyzed by iTRAQ(Isobaric tags for relative and absolute quantification) technology. Western blotting and immunohistochemical staining were used to verify Periostin expression in the tissues of PCa. Periostin expression in different PCa cell lines was determined by immunofluorescence staining, western blotting and reverse transcription PCR(RT-PCR). The LNCap cells with Periostin expression were used for transfecting shRNA-Periostin lentiviral particles. The efficancy of transfecting shRNA lentiviral particles was evaluated by immunofluorescence, western blotting and Real-time PCR. The effect of silencing Periostin expression by RNAi on proliferation of LNCap cells was determined by MTT assay and tumor xenografts. The tissue slices from theses xenografts were analyzed by hematoxylin and eosin(HE) staining. The expression of Periostin in the xenografts was deteminned by Immunohistochemical staining and western blotting. The migration of LNCap cells after silencing Periostin gene expression were analyzed in vitro.

Results

Periostin as the protein of interest was shown 9.12 fold up-regulation in PCa compared with BPH. The overexpression of Periostin in the stroma of PCa was confirmed by western blotting and immunohistochemical staining. Periostin was only expressed in PCa LNCap cell line. Our results indicated that the transfection ratio was more than 90%. As was expected, both the protein level and mRNA level of Periostin in the stably expressing shRNA-Periostin LNCap cells were significantly reduced. The stably expressing shRNA-Periostin LNCap cells growed slowly in vitro and in vivo. The tissues of xenografts as PCa were verificated by HE staining. Additionally, the weak positive Periostin expressed tumor cells could be seen in the tissues of 6 xenografts from the group of down-regulated Periostin LNCap cells which had a significant decrease of the amount of Periostin compared to the other two group. Furthermore, our results demonstrated that sliencing Periostin could inhibit migration of LNCap cells in vitro.

Conclusions

Our data indicates that Periostin as an up-regulated protein in PCa may be a promising target of therapeutical intervention for PCa in future.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.