IL6 and breast cancer: The aim of this study was to establish a collection of breast cancer PDXs that retain the immunohistochemical and molecular characteristics of the original tumor, to assess the relationship between the engraftment of the tumors and the outcome of breast cancer PDXs, to analyze the effect of anti-IL-6 antibodies on their growth and develop an assay to select tumors that depend on IL-6 signaling to grow.