title: Selective gene-expression profiling of migratory tumor cells in vivo predicts clinical outcome in breast cancer patients.
abstract: BACKGROUND
  Metastasis of breast cancer is the main cause of death in patients. Previous genome-wide studies have identified gene-expression patterns correlated with cancer patient outcome. However, these were derived mostly from whole tissue without respect to cell heterogeneity. In reality, only a small subpopulation of invasive cells inside the primary tumor is responsible for escaping and initiating dissemination and metastasis. When whole tissue is used for molecular profiling, the expression pattern of these cells is masked by the majority of the noninvasive tumor cells. Therefore, little information is available about the crucial early steps of the metastatic cascade: migration, invasion, and entry of tumor cells into the systemic circulation.
  
  
  METHODS
  In the past, we developed an in vivo invasion assay that can capture specifically the highly motile tumor cells in the act of migrating inside living tumors. Here, we used this assay in orthotopic xenografts of human MDA-MB-231 breast cancer cells to isolate selectively the migratory cell subpopulation of the primary tumor for gene-expression profiling. In this way, we derived a gene signature specific to breast cancer migration and invasion, which we call the Human Invasion Signature (HIS).
  
  
  RESULTS
  Unsupervised analysis of the HIS shows that the most significant upregulated gene networks in the migratory breast tumor cells include genes regulating embryonic and tissue development, cellular movement, and DNA replication and repair. We confirmed that genes involved in these functions are upregulated in the migratory tumor cells with independent biological repeats. We also demonstrate that specific genes are functionally required for in vivo invasion and hematogenous dissemination in MDA-MB-231, as well as in patient-derived breast tumors. Finally, we used statistical analysis to show that the signature can significantly predict risk of breast cancer metastasis in large patient cohorts, independent of well-established prognostic parameters.
  
  
  CONCLUSIONS
  Our data provide novel insights into, and reveal previously unknown mediators of, the metastatic steps of invasion and dissemination in human breast tumors in vivo. Because migration and invasion are the early steps of metastatic progression, the novel markers that we identified here might become valuable prognostic tools or therapeutic targets in breast cancer.
authors.forename: Antonia
authors.initials: A
authors.lastname: Patsialou
authors.forename: Yarong
authors.initials: Y
authors.lastname: Wang
authors.forename: Juan
authors.initials: J
authors.lastname: Lin
authors.forename: Kathleen
authors.initials: K
authors.lastname: Whitney
authors.forename: Sumanta
authors.initials: S
authors.lastname: Goswami
authors.forename: Paraic A
authors.initials: PA
authors.lastname: Kenny
authors.forename: John S
authors.initials: JS
authors.lastname: Condeelis
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology*; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics; D015331:Cohort Studies; D004195:Disease Models, Animal; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D053263:Gene Regulatory Networks; D064593:Heterografts; D006801:Humans; D009361:Neoplasm Invasiveness; D063868:Patient Outcome Assessment; D011379:Prognosis; D015203:Reproducibility of Results; D059467:Transcriptome