Background: The study of breast cancer metastasis depends on the use of established breast cancer cell lines that\r\ndo not accurately represent the heterogeneity and complexity of human breast tumors. A tumor model was\r\ndeveloped using primary breast tumor-initiating cells isolated from patient core biopsies that would more\r\naccurately reflect human breast cancer metastasis.\r\nMethods: Tumorspheres were isolated under serum-free culture conditions from core biopsies collected from five\r\npatients with clinical diagnosis of invasive ductal carcinoma (IDC). Isolated tumorspheres were transplanted into the\r\nmammary fat pad of NUDE mice to establish tumorigenicity in vivo. Tumors and metastatic lesions were analyzed\r\nby hematoxylin and eosin (H) staining and immunohistochemistry (IHC).\r\nResults: Tumorspheres were successfully isolated from all patient core biopsies, independent of the estrogen\r\nreceptor a (ERa)/progesterone receptor (PR)/Her2/neu status or tumor grade. Each tumorsphere was estimated to\r\ncontain 50-100 cells. Transplantation of 50 tumorspheres (1-5 Ã?â?? 103 cells) in combination with Matrigel into the\r\nmammary fat pad of NUDE mice resulted in small, palpable tumors that were sustained up to 12 months postinjection.\r\nTumors were serially transplanted three times by re-isolation of tumorspheres from the tumors and\r\ninjection into the mammary fat pad of NUDE mice. At 3 months post-injection, micrometastases to the lung, liver,\r\nkidneys, brain and femur were detected by measuring content of human chromosome 17. Visible macrometastases\r\nwere detected in the lung, liver and kidneys by 6 months post-injection. Primary tumors variably expressed\r\ncytokeratins, Her2/neu, cytoplasmic E-cadherin, nuclear b catenin and fibronectin but were negative for ERa and\r\nvimentin. In lung and liver metastases, variable redistribution of E-cadherin and b catenin to the membrane of\r\ntumor cells was observed. ERa was re-expressed in lung metastatic cells in two of five samples.\r\nConclusions: Tumorspheres isolated under defined culture conditions from patient core biopsies were tumorigenic\r\nwhen transplanted into the mammary fat pad of NUDE mice, and metastasized to multiple mouse organs.\r\nMicrometastases in mouse organs demonstrated a dormancy period prior to outgrowth of macrometastases. The\r\ndevelopment of macrometastases with organ-specific phenotypic distinctions provides a superior model for the\r\ninvestigation of organ-specific effects on metastatic cancer cell survival and growth.
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