Colonic metastasis from carcinoma of the breast that mimics a primary intestinal cancer

Although the lung, liver, or bones are the most common location for distant metastases in breast cancer patients, metastases to the intestinal tract are very rarely recognized in the clinic. We will present an unusual case of colonic metastasis from a carcinoma of the breast that mimics a primary intestinal cancer, along with a through review of English language medical literature. Despite the fact that isolated gastrointestinal (GI) metastases are very rare and much less common than benign disease processes or second primaries of the intestinal tract in patients with a history of breast cancer, metastatic disease should be given consideration whenever a patient experiences GI symptoms.     

乳腺微钙化促进乳腺癌骨转移的研究进展

乳腺癌是女性发病率最高的癌症,在过去的十年中,全球发病率持续上升,死亡率高居不下.最新的统计学研究表明,仅2018年,全球范围内检测出约210万乳腺癌病例,其中近63万患者死亡,因而也是女性死亡率最高的癌症[1].然而,许多癌症患者的死亡并非由于肿瘤在原发部位生长,而是在于肿瘤侵袭或转移至其他部位,其中乳腺癌最容易发生...     

Breast cancer cell surface annexin II induces cell migration and neoangiogenesis via tPA dependent plasmin generation

Annexin II, an abundant phospholipids binding cell surface protein, binds tPA and functions as a regulator of fibrinolysis. Annexin II also mediates angiogenesis and enhances tumor growth and metastasis. However, the mechanism supporting this role is not known. Using human breast cancer model we show that invasive human breast cancer cells (MDA-MB231) synthesize annexin II and tissue plasminogen activator (tPA). In vitro both annexin II and tPA interacts which in turn convert zymogen plasminogen to reactive enzyme plasmin. Cell surface produced plasmin inhibited the migration of MDA-MB231 cells. Silencing of annexin II gene in MDA-MB231 cells abolished tPA binding therefore inhibited tPA dependent plasmin generation. These annexin II suppressed MDA-MB231 cells showed reduced motility. Immunohistochemical analysis of prediagnosed clinical specimens showed abundant secretion of tPA and expression of annexin II on the surface of invasive human breast cancer cells which correlates with neovascularization of the tumor. Taken together, these data indicate that annexin II may regulate localized plasmin generation in breast cancer. This may be an early event switching breast cancer from the prevascular phase to the vascular phase and thus contributing to aggressive cancer with the possibility of metastasis. The data provide a mechanism explaining the role of annexin II in breast cancer progression and suggest that annexin II may be an attractive target for therapeutic strategies aimed to inhibit angiogenesis and breast cancer.     

Primary tumour expression of the cysteine cathepsin inhibitor Stefin A inhibits distant metastasis in breast cancer

Using the clinically relevant 4T1-derived syngeneic murine model of spontaneous mammary metastasis to bone, we have identified the cysteine cathepsin inhibitor Stefin A as a gene differentially expressed in primary and metastatic mammary tumours. In primary tumours, Stefin A expression correlated inversely with metastatic potential in 4T1-derived lines and was not detected in tumour cells in culture, indicating induction only within the tumour microenvironment. Enforced expression of Stefin A in the highly metastatic 4T1.2 cell line significantly reduced spontaneous bone metastasis following orthotopic injection into the mammary gland. Consistent with the mouse data, Stefin A expression correlated with disease-free survival (absence of distant metastasis) in a cohort of 142 primary tumours from breast cancer patients. This was most significant for patients with invasive ductal carcinoma expressing Stefin A, who were less likely to develop distant metastases (log rank test, p = 0.0075). In a multivariate disease-free survival analysis (Cox proportional hazards model), Stefin A expression remained a significant independent prognostic factor in patients with invasive ductal carcinoma (p = 0.0014), along with grade and progesterone receptor (PR) status. In human lung and bone metastases, we detected irregular Stefin A staining patterns, with expression often localizing to micrometastases (<0.2 mm) in direct contact with the stroma. We propose that Stefin A, as a cysteine cathepsin inhibitor, may be a marker of increased cathepsin activity in metastases. Using immunohistology, the cathepsin inhibitor was detected co-expressed with cathepsin B in lung and bone metastases in both the murine model and human tissues. We conclude that Stefin A expression reduces distant metastasis in breast cancer and propose that this may be due to the inhibition of cysteine cathepsins, such as cathepsin B.     

Overexpression of c-Myc and Bcl-2 during progression and distant metastasis of hormone-treated breast cancer

The aim of this study was to identify molecules involved in the proliferation and survival of recurrent estrogen receptor (ER)-positive breast cancer at the site of metastasis. Most studies of biomarkers are done using the initial primary breast tumor whereas pathological studies of breast cancer lesions after distant recurrence are scarce. Here we evaluated the expression of the oncogenes c-Myc and Bcl-2, mediators of estrogen-dependent proliferation and survival, during breast cancer progression and relapse after adjuvant hormonal therapy. Using a preclinical model of tamoxifen-resistant growth, we found overexpression of c-Myc in all (3/3) and of Bcl-2 in most (2/3) tamoxifen resistant-breast cancer variants. To determine whether c-Myc and Bcl-2 are expressed during breast cancer progression in the clinics we identified breast cancer patients who had received adjuvant hormonal therapy for the treatment of their localized disease and had later experienced relapse. From 583 patients who had received adjuvant hormonal therapy a total of 82 experienced recurrence. Nevertheless, only 22 patients had had a biopsy of their metastatic lesion done after relapse. Twenty-one biopsies were useful for this biomarker study. These biopsies were obtained mostly (20) from breast cancer patients who had received tamoxifen as their adjuvant hormonal therapy. One patient had received an aromatase inhibitor instead. Our results showed that almost all (20) metastatic recurrences expressed ER. Expression of c-Myc was observed in 18 out of 19 metastatic lesions scored while expression of Bcl-2 was detected in 17 out of 21 metastatic tumors. A correlation between ER expression and Bcl-2, but not with c-Myc, was found in these recurrent metastatic lesions. In addition, c-Myc expression was correlated with the nuclear grade of the metastatic lesion. Thus, the frequent expression of c-Myc and Bcl-2 in metastatic breast cancer recurrences suggests that combining hormonal therapy with strategies to block c-Myc and Bcl-2 may prevent growth of ER-positive breast cancer at the site of metastasis.     

Bone metastasis: evaluation of 1100 patients with breast cancer

The aim of this study is to determine the relationship between the demographics and the clinical characteristics of breast cancer (BC) patients with bone metastasis (BM). The study included 1100 BC patients, of whom 174 had BMs and 926 had no BMs. Immunohistochemical methods were employed to understand estrogen receptor (ER)/progesterone receptor (PgR) receptor levels, Ki-67 protein levels and human epidermal growth factor receptor 2 (HER2) expression levels. Data were collected based on the hospital records of these patients, and ultrasonography or magnetic resonance imaging (MRI) results were employed for tumor localization. Positron emission tomography (PET)-computed tomography (CT) data were employed for the BM evaluation. The mean age (P = 0.067) and tumor diameter (P = 0.022) of BC cases who showed BM were significantly different from those who did not show BM. In addition, a significant relationship between the tumor diameter (P = 0.001) and axillary lymph node (ALN) number (P = 0.000) and BM was observed. The percentages of ER and PgR (r = 0.639; P = 0.000) were positively correlated, while the percentage of ER and Ki-67 protein levels (r = -0.505; P = 0.000) were negatively correlated. However, these correlations were not significant between the groups. The tumor diameter and positive ALNs may have an important role in BM of BC. There was no significant effect of ER/PgR receptor levels, Ki-67 protein levels, or HER2 expression levels in BMs of BC.     

A novel orthotopic model of breast cancer metastasis to bone

Breast cancer affects approximately one woman in twelve and kills more women than any other cancer. If detected early, patients have a five year survival rate of 66%, but once metastatic disease has developed, there is no effective treatment. About 70% of patients with metastatic disease have bone involvement, while lungs and liver are the other common targets. Bone metastases cause severe pain, pathological fractures and hypercalcaemia and thus are a significant clinical problem. The development of new therapies for metastatic breast carcinoma depends on a better understanding of the mechanism of homing of the tumour cells to bone, liver and lungs and the factors required for their growth in these organs. Research on mechanisms of breast cancer metastasis, particularly to bone, has relied on in vitro studies or on tumour models in which the inoculation route is designed to promote delivery of tumour cells to a specific organ. Metastases in bone are achieved by inoculation into the right ventricle of the heart. To our knowledge there has been no report of a model of metastatic spread from the mammary gland to distant sites which reliably includes bone. In this paper, we describe our recent development of a novel murine model of metastatic breast carcinoma. The new model is unique in that the pattern of metastatic spread closely resembles that observed in human breast cancer. In particular, these murine breast tumours metastasise to bone from the primary breast site and cause hypercalcaemia, characteristics not normally found in murine tumours, but common in human disease. Furthermore, in a preliminary characterisation of this model, we show that secretion of parathyroid hormone-related protein, a role for which has been implicated in breast cancer spread to bone, correlates with metastasis to bone. This model therefore provides an excellent experimental system in which to investigate the factors that control metastatic spread of breast cancer to specific sites, particularly bone. The special advantage of this system is that it involves the whole metastasis process, beginning from the primary site. Existing models consider mechanisms that pertain to growth of tumour once the site has been reached. An understanding of the regulation of these factors by potential therapeutic agents could lead to improvement in therapies designed to combat metastatic disease. For the first time, this development will allow exploration of the molecular basis of site-specific metastasis of breast cancer to bone in a clinically relevant model.     

Metastasis of breast cancer to renal cancer: report of a rare case

Tumor-to-tumor metastasis (TTM) is a rare phenomenon. We present a case of an invasive ductal carcinoma (IDC) of the breast metastasizing to a clear cell renal cell carcinoma (RCC). Breast cancer (BC) metastasis to the RCC is rarely reported, especially in resected kidney tumor. In several cases reported, IDC was the exclusively histologic type of BC metastasized to RCC. It seems that the different molecular type of IDC doesn’t affect the metastatic tendencies to RCC. TTM was an indicator of diffuse disease. For any patient with a history of breast cancer, especially with multi-organs metastasis, resection of kidney tumor should be carefully considered.     

The role of tumor-associated macrophages in breast carcinoma invasion and metastasis

The main purpose of this study was to investigate the infiltration of tumor-associated macrophages (TAMs) in normal and malignant breast tissue and the draining lymph nodes, and to explore its effect on breast cancer invasion and metastasis. The infiltration densities of TAMs was observed using immunohistochemical staining of CD68 in 100 cases of breast cancer specimens and its paired adjacent non-cancer breast tissues and draining lymph modes, and then to evaluate the relation of TAMs to various clinicopathological features including patients prognosis in breast carcinoma. We observed the infiltration densities of TAMs were significantly higher in breast carcinoma tissue than in adjacent normal tissue and significantly higher in much larger size and higher stage cases. Furthermore, infiltration densities of TAMs have negative correlation with the 5-year survival rates of breast cancer patients. But in matched lymph-nodes, the infiltration densities of TAMs were significantly lower in cancerous metastatic lymph-node samples than in non-metastatic one. Therefore, our data suggests that TAMs infiltration in primary tumor promote invasion and lymphatic metastasis of breast cancer and have negative correlation with patients prognosis in breast cancer, but in lymph-node TAMs may play another role and need further study in the future.     

Expression of Yes-associated protein (YAP) in metastatic breast cancer

The purpose of this study was to investigate the expression of Yes-associated protein (YAP) in different metastatic sites in metastatic breast cancer and to determine the clinical implications of these patterns. Immunohistochemical staining was used to investigate the expression of YAP and phospho-YAP in tissue microarrays from 122 cases of metastatic breast cancer (bone metastasis = 29, brain metastasis = 38, liver metastasis = 12, and lung metastasis = 43). The expression levels of YAP and phospho-YAP differed according to the metastatic site in metastatic breast cancer. Specifically, nuclear expression of phospho-YAP was high in brain metastasis but low in lung metastasis (P = 0.010). The effects of YAP and phospho-YAP expression on clinical outcomes were investigated by univariate analysis. This analysis showed that nuclear YAP positivity (P = 0.008) and nuclear phospho-YAP positivity (P = 0.003) were both associated with shorter overall survival. In conclusion, the level of YAP expression varies according to the metastatic site in metastatic breast cancer. Moreover, high YAP expression was correlated with poor prognosis.     

基质金属蛋白酶-2酶活性与乳腺癌浸润、转移的关系

目的：探讨基质金属蛋白酶-2（MMP-2，72 kD、62 kD）的活性与乳腺癌侵润、转移的关系。方法：利用酶谱和计算机软件检测并分析了35例乳腺癌组织中MMP-2活性。结果：乳腺癌MMP(72 kD)的水平低于乳腺癌,P<0.05；MMP(62 kD+72 kD)乳腺纤维腺瘤与乳腺癌比较时，P>0.05。同时发现MMP(62kD)乳腺癌组(13.83±4.53)明显高于乳腺纤维腺瘤(6.89±2.94)，P<0.05；MMP(62 kD/62 kD+72 kD):乳腺癌组(0.48)明显高于乳腺纤维瘤(0.24)，P<0.01；转移组(0.61)明显高于无转移组(0.42)，P<0.01；浸润组(0.48)明显高于非浸润组(0.36)，P<0.01。结论：MMP-2的活性水平与乳腺癌的侵袭、转移有关。     

Nanodiamonds-mediated doxorubicin nuclear delivery to inhibit lung metastasis of breast cancer

Lung metastasis is one of the greatest challenges for breast cancer treatment. Here, a nanodiamonds (NDs)-mediated doxorubicin (DOX) delivery system was first designed to inhibit the lung metastasis of breast cancer effectively. DOX was non-covalently bound to NDs via physical adsorption in an aqueous solution, then DSPE-PEG 2K was coated to the NDs-DOX complex (NDX) to increase the dispersibility and prolong the circulation time. DSPE-PEG 2K coating NDX (DNX) displayed high drug loading and excellent ability to deliver DOX to the nucleus, thereby significantly enhancing cytotoxicity and inducing cell apoptosis. Furthermore, DNX showed good histocompatibility and could improve drug accumulation in lung, as a result, markedly inhibited the lung metastasis of breast cancer. The high anti-metastasis efficacy with the decreased systemic toxicity suggested that DNX could be a promising drug delivery system for the therapy of lung metastasis of breast cancer.     

Hyaluronan synthase 2 overexpression is correlated with the tumorigenesis and metastasis of human breast cancer

Extracellular matrix (ECM) is closely correlated with the malignant behavior of breast cancer cells. Hyaluronan (HA) is one of the main components of ECM, and actively regulates cell adhesion, migration and proliferation by interacting with specific cell surface receptors such as CD44 and RHAMM. HA synthase 2 (HAS2) catalyzes the sysnthesis of HA, but its role in breast tumorigenesis remains unclear. This study assessed the roles of HAS2 in malignant behavior of human breast cancer and sought to provide mechanistic insights into the biological and pivotal roles of HAS2. We observed HAS2 was overexpressed in breast cancer cell lines and invasive duct cancer tissues, compared with the nonmalignant breast cell lines and normal breast tissues. In addition, a high level of HAS2 expression was statistically correlated with lymph node metastasis. Functional assays showed that knockdown of HAS2 expression inhibited breast tumor cell proliferation in vivo and in vitro, through the induction of apoptosis or cell cycle arrest. Further studies showed that the HA were elevated in breast cancer, and HAS2 could upregulate HA expression. In conclusion, HAS2-HA system influences the biological characteristics of human breast cancer cells, and HAS2 may be a potential prognostic marker and therapeutic target in breast cancer.     

Surviving at a distant site: The organotropism of metastatic breast cancer

Many cancers demonstrate a non-random distribution of sites for distant relapse while others have the propensity to metastasize to multiple organ systems. One of the notable recent findings is that the breast cancer subtypes differ not only in their biological characteristics as primary tumors but also in their capacity for metastatic progression. This information could potentially be utilized in treatment decision making and surveillance strategies.     

Increased COX2 expression enhances tumor-induced osteoclastic lesions in breast cancer bone metastasis

Metastasis is a complicated process that depends largely on the interaction of primary tumors and the local host environment. In this study, we have established a new mouse model to mimic the process of tumor metastasis in breast cancer patients. TM40D-MB mouse mammary tumor cells were transplanted to the mammary glands of syngeneic mice. Mammary tumors developed in the glands in situ and were metastatic to bone with over 53% efficiency. We compared the gene expression profile of high (TM40D-MB) vs. low metastatic (TM40D) tumor cells using Affymetrix microarray chips. Microarray analysis revealed a list of genes that were consistently up-/down-regulated in TM40D-MB tumor cells. One of the genes, COX2 was selected for functional study. Injection of TM40D-COX2 cells to mouse femur caused a significant increase in bone destruction compared to TM40D-C control, as measured by the micro-computed tomography (microCT) scanning for the trabecular bone volume. In vitro assays showed that COX2 significantly increased the rate of osteoclast formation, and this effect was reversible by the specific COX2 inhibitor NS-398. These data indicate that COX2 is one gene important for breast cancer bone metastasis. The availability of this mouse model and the comparative study of gene expression signatures between TM40D and other bone metastasis models will likely generate important information about common pathways for breast cancer bone metastasis. Further functional studies of metastasis signature genes should help to develop means to curb the metastasis process.     

Bone resorption increases tumour growth in a mouse model of osteosclerotic breast cancer metastasis

Osteosclerotic metastases account for 20% of breast cancer metastases with the remainder osteolytic or mixed. In mouse models, osteolytic metastases are dependent on bone resorption for their growth. However, whether the growth of osteosclerotic bone metastases depends on osteoclast or osteoblast actions is uncertain. In this study, we investigate the effects of high and low bone resorption on tumour growth in a mouse model of osteosclerotic metastasis. We implanted human breast cancer, MCF-7, cells into the tibiae of mice. Low and high levels of bone resorption were induced by osteoprotegerin (OPG) treatment or calcium deficient diet respectively. We demonstrate that OPG treatment significantly reduces tumour area compared to vehicle (0.42 +/- 0.06 vs. 1.27 +/- 0.16 mm2, P < 0.01) in association with complete inhibition of osteoclast differentiation. In contrast, low calcium diet increases tumour area compared to normal diet (0.90 +/- 0.30 vs. 0.58 +/- 0.20 mm2, P < 0.05) in association with increased osteoclast numbers (84.44 +/- 5.18 vs. 71.11 +/- 3.56 per mm2 bone lesion area, P < 0.05). Osteoblast surfaces and new woven bone formation were similarly increased within the tumour boundaries in all treatment groups. Tumour growth in this model of osteosclerotic metastasis is dependent on ongoing bone resorption, as has been observed in osteolytic models. Bone resorption, rather than bone formation, apparently mediates this effect as osteoblast surfaces in the tumour mass were unchanged by treatments. Treatment of breast cancer patients through correction of calcium deficiency and/or with anti-resorptive agents such as OPG, may improve patient outcomes in the adjuvant as well as palliative settings.     

Gene delivery of TIPE2 inhibits breast cancer development and metastasis via CD8+ T and NK cell-mediated antitumor responses

Breast cancer is the second leading cause of cancer-related deaths in the female patients which was mainly caused by metastasis. Development of target gene therapy for breast cancer to suppress tumor progress and metastasis will improve the therapeutic options and be of great benefit to the patients. Tumor necrosis factor-alpha-induced protein 8-like 2 is a novel molecule for maintaining immune homeostasis and is involved in cancer development. In the present study, we overexpressed TIPE2 in breast cancer cells to investigate the role of TIPE2 in the development of breast cancer. Our results showed that overexpression of TIPE2 significantly inhibited the proliferation of 4T1 cells in vitro and in vivo. We constructed a non-viral targeted gene therapeutic system by using the minicircle plasmids expressing TIPE2. We found that the growth and metastasis of breast cancer was significantly inhibited by hydrodynamic gene delivery of TIPE2 plasmids in vivo. Mechanistically, TIPE2 increased T and NK cells, and decreased MDSCs. Gene delivery of TIPE2 up-regulated the production of IFN-γ and TNF-α by CD8⁺ T and NK cells in spleens and tumor microenvironment, and enhanced the cytotoxic activity of CD8⁺ T and NK cells. Taken together, TIPE2 inhibited breast cancer development and metastasis possibly via promoting CD8⁺ T and NK cell-mediated antitumor immune responses. Thus, the results indicate that TIPE2 may be a potential therapeutic target for breast cancer therapy.     

乳腺原发癌和淋巴结转移癌干细胞Hedgehog信号通路相关基因的比较

目的:探讨Hedgehog信号通路相关基因在乳腺原发癌干细胞与其相应的淋巴结转移癌干细胞中的表达及意义。方法:收集新鲜的乳腺癌标本,经快速病理诊断为乳腺浸润性导管癌,且伴有腋窝淋巴结的转移,采用免疫磁珠分选法分别提取乳腺原发癌与淋巴结转移癌干细胞,采用Real-time PCR检测Hedgehog信号通路相关基因Shh、Ptch、Smo和Gli-1在乳腺原发癌干细胞与相应转移癌干细胞中的表达。结果:Shh在乳腺原发癌干细胞和相应淋巴结转移癌干细胞中的表达没有统计学意义;Ptch在乳腺原发癌干细胞的表达明显高于转移癌干细胞,而Smo、Gli-1在乳腺原发癌干细胞的表达明显低于转移癌干细胞。结论:与乳腺原发癌干细胞相比,转移癌干细胞Hedgehog信号通路处于更高的活化状态,从而具有更强的侵袭和转移能力,有可能成为新的治疗靶点。     

NDRG1基因与乳腺癌转移的关系及其转染对乳腺癌细胞株增殖及侵袭力的影响

目的探讨NDRG1基因与乳腺癌转移的关系及其转染对乳腺癌细胞株增殖及侵袭力的影响。方法免疫组织化学SP法、即时荧光定量逆转录聚合酶链反应(real time RT-PCR)检测10例新鲜乳腺浸润性导管癌和27例石蜡包埋乳腺癌组织中NDRG1蛋白和mRNA的表达。脂质体介导NDRG1基因瞬时转染高侵袭高转移性人乳腺癌细胞株MDA-MB-231;用5-溴-2-脱氧尿苷(BrdU)掺入法、流式细胞术观察NDRG1基因转染后对细胞增殖和细胞周期的影响;细胞体外侵袭实验和迁移实验观察转染后细胞侵袭和迁移能力的变化。结果NDRG1蛋白和mRNA表达分别为:无转移的乳腺癌组织阳性率为100%(14/14)和0·82±0·14,而有转移的乳腺癌组织中为69·2%(9/13)和0·17±0·11,均明显降低;对两株细胞的检测中,高侵袭高转移的MDA-MB-231细胞株中NDRG1mRNA的表达水平(0·14±0·02)明显低于低侵袭低转移的MCF7细胞株(1·51±0·11)。NDRG1基因瞬时转染MDA-MB-231细胞后,与未转染组和pEGFP-N3组相比,pEGFP-NDRG1-N3转染组中,细胞BrdU掺入率降低,细胞周期G0/G1期比例增高,S期比例明显减低;同时细胞体外侵袭能力下降,而体外迁移能力则差异无统计学意义。结论NDRG1基因的表达与乳腺癌的转移呈负相关关系,提示该基因可望成为早期预测乳腺癌转移的分子生物学标记物之一;NDRG1基因通过脂质体转染高侵袭高转移性人乳腺癌MDA-MB-231细胞株,可抑制肿瘤细胞增殖、降低其侵袭能力,提示其可作为一个候选的肿瘤转移抑制基因,并有望成为乳腺癌基因治疗的新的候选基因。     

Inhibition of RANKL blocks skeletal tumor progression and improves survival in a mouse model of breast cancer bone metastasis

Bone metastases cause severe skeletal morbidity including fractures and hypercalcemia. Tumor cells in bone induce activation of osteoclasts, which mediate bone resorption and release of growth factors from bone matrix, resulting in a “vicious cycle” of bone breakdown and tumor proliferation. Receptor activator of NF-κB ligand (RANKL) is an essential mediator of osteoclast formation, function, and survival, and is blocked by a soluble decoy receptor, osteoprotegerin (OPG). In human malignancies that metastasize to bone, dysregulation of the RANK/RANKL/OPG pathway can increase the RANKL:OPG ratio, a condition which favors excessive osteolysis. In a mouse model of bone metastasis, RANKL protein levels in MDA-MB-231 (MDA-231) tumor-bearing bones were significantly higher than tumor-free bones. The resulting tumor-induced osteoclastogenesis and osteolysis was dose-dependently inhibited by recombinant OPG-Fc treatment, supporting the essential role for RANKL in this process. Using bioluminescence imaging in a mouse model of metastasis, we monitored the anti-tumor efficacy of RANKL inhibition on MDA-231 human breast cancer cells in a temporal manner. Treatment with OPG-Fc in vivo inhibited growth of MDA-231 tumor cells in bony sites when given both as a preventative (dosed day 0) and as a therapeutic agent for established bone metastases (dosed day 7). One mechanism by which RANKL inhibition reduced tumor burden appears to be indirect through inhibition of the “vicious cycle” and involved an increase in tumor cell apoptosis, as measured by active caspase-3. Here, we demonstrate for the first time that OPG-Fc treatment of mice with established bone metastases resulted in an overall improvement in survival.