Abstract 5210: Impact of tumor microenvironment on expansion of tumor initiating cells in breast cancer metastasis

Breast cancer metastasis which ultimately results in breast cancer death, is an event believed to be initiated by the migration of tumor initiating cells (TIC) from the primary tumor to niches for micrometastatic disease. Recent data suggests the tumor microenvironment promotes TIC. The clinical relevance of secreted factors from the microenvironment on TIC surrogate, mammosphere (MS) formation and MS sensitivity to drug therapy was investigated using breast cancer patient fluids inherently conditioned by the tumor microenvironment: post-operative seromas and malignant pleural effusions. Fluids from 20 patients with breast cancer (8 seromas and 13 pleural effusions) and mesenchymal stem cells (MSC) from healthy donors were collected on IRB approved protocols. Cellular components were eliminated from patient-derived fluids using density-gradient centrifugation. MSC conditioned media (MSC-CM) was collected from 3D cultures of primary MSC. Luminex multiplex array platform was used to characterize 79 cytokine and growth factor components of all fluids. In addition, MSC-CM and patient-derived fluids were added to cultures of breast cancer cell lines: MCF-7, an estrogen receptor (ER)-positive cell line; SUM149, a triple-negative inflammatory breast cancer cell line; and SUM159, a triple-negative metaplastic breast cancer cell line and MS forming efficiency was examined. Our results show that pleural effusions and seromas are enriched for factors also secreted by MSC such as MCP-1, GRO, IL-6 and IL-8. We found remarkable similarities regarding the cytokines and growth factors profile in pleural effusions and seromas. Both patient-derived fluids have comparable amount of IL-2, IL-3, IL-4 and IL-10, as well as, VEGF, EGF and FGF-b. IL-1β and IL-16 were significantly different between pleural effusions and seromas. Seroma fluid from bilateral drains in a patient with an invasive cancer and a contralateral benign mastectomy had very similar cytokine concentrations. Moreover, MSC-CM and pleural fluids from ER+ and ER- patients increased the MS formation efficiency of both triple-negative cell lines while seroma fluids from ER+ and ER- patients increased the MS formation efficiency of ER-positive cell line MCF-7. Finally, we evaluated the impact of a panel of drugs on cell cultures grown with MSC-CM and patient-derived fluids. We found that the effect of chemotherapies on MS formation can be attenuated by patient-derived fluids. Seroma and pleural effusion fluids from breast cancer patients have similar cytokine profiles, change MS formation efficiency of standard breast cancer cell models, and mediate sensitivity to therapy. Here we demonstrate that host and microenvironmental factors are critical for determining resistance to therapy. Future studies will investigate the prognostic implications of factors that promote TIC survival in the fluid tumor microenvironment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5210. doi:1538-7445.AM2012-5210