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Introduction: Inflammatory breast cancer (IBC) is the most metastatic variant of breast cancer with the poorest survival in all types of breast cancer patients and presently therapeutic targets for IBC are very limited. Enhancer of zeste homolog 2 (EZH2) is frequently expressed in human IBC and its expression positively correlates with worse clinical outcome. However, the molecular basis for EZH2 promoting IBC has not been explored. Here, we investigated the functional role of EZH2 in IBC cells by examining the effects of its knockdown on the formation of tumor spheroids and invasion of these cells in vitro and in vivo in an orthotopic xenograft model. Methods: SUM149 and a new IBC cell line-FC-IBC-02 derived from pleural effusion fluid of an IBC patient were used in this study. Specific knockdown of EZH2 was performed using short hairpin RNA (shRNA) specific to the human EZH2 gene. Cell growth and the formation of tumor spheroids were examined in vitro. The effects of EZH2 knockdown on IBC cell migration and invasion were examined by a Boyden chamber assay. For the in vivo tumor growth studies, IBC cells were orthotopically transplanted into the mammary fat pads of immunodeficient mice. Results: The results showed that EZH2 is expressed at higher levels in human IBC cell lines compared with normal human mammary epithelial cells, and the knockdown of EZH2 expression significantly suppressed cell growth and tumor spheroid formation of human IBC cells in vitro. In addition, EZH2 knockdown inhibited the migration and invasion of IBC cells. Significantly, EZH2 knockdown suppressed the angiogenesis and tumor growth of IBC cells in vivo. Conclusions: Our results provide direct evidence that EZH2 is critical for the formation of tumor spheroids and invasion of human IBC cells and could be a potential target for developing novel therapeutic strategies for human IBC. [ABSTRACT FROM AUTHOR]

Metastatic breast cancer (MBC) is characterized by a combination of tumor growth, proliferation and metastatic progression and is typically managed with palliative intent. The benefit of standard systemic therapies is relatively limited and the disease is considered incurable suggesting the need to investigate the biological drivers of the various phases of the metastatic process in order to improve the selection of molecularly driven therapies. The detection, enumeration and molecular analysis of circulating tumor cells (CTCs) provide an intriguing opportunity to advance this knowledge. CTCs enumerated by the Food and Drugs Administration-cleared CellSearch(®) system are an independent prognostic factor of progression-free survival (PFS) and overall survival (OS) in MBC patients. Several published papers demonstrated the poor prognosis for MBC patients that presented basal CTC count ≥5 in 7.5 mL of blood. Therefore, the enumeration of CTCs during treatment for MBC provides a tool with the ability to predict progression of disease earlier than standard timing of anatomical assessment using conventional radiological tests. During the metastatic process cancer cells exhibit morphological and phenotypic plasticity undergoing epithelial-mesenchymal transition (EMT). This important phenomenon is associated with down regulation of epithelial marker (e.g., EpCAM) with potential limitations in the applicability of current CTCs enrichment methods. Such observations translated in a number of investigations aimed at improving our capabilities to enumerate and perform molecular characterization of CTCs. Theoretically, the phenotypic analysis of CTCs can represent a "liquid" biopsy of breast tumor that is able to identify a new potential target against the metastatic disease and advanced the development and monitoring of personalized therapies.