Towards understanding breast cancer mechanisms to metastasize. Homo sapiens

How organ-specific metastatic traits accumulate in primary tumors remains unknown. We identified a role of the primary tumor stroma in selecting breast cancer cells that are primed for metastasis in the bone. A fibroblast-rich stroma in breast tumors creates a microenvironment that is similar to that of bone metastases in its abundance of the cytokines CXCL12 and IGF1. Heterogeneous breast cancer cell populations growing in such mesenchymal environment evolve towards a preponderance of clones that thrive on CXCL12 and IGF1. Fibroblast-driven selection of bone metastatic clones in mammary tumors is suppressed by CXCL12 and IGF1 receptor inhibition. Thus, a fibroblast-rich stroma in breast tumors can pre-select bone metastatic seeds, promoting the evolution of metastatic traits and the interplay between a primary tumor and its distant metastases. Overall design: Affymetrix U133 Plus2 arrays were hybridized according to the manufacturer's procedure using RNA extracted from 47 primary breast tumors. Specific gene sets were evaluated in this cohort.