IL6 and breast cancer: From the observations within this research we conclude that: (1) MCs traffic to mammary carcinoma that is IL-6 deficient in vivo (in the mouse 4T1 model); (2) upon further analysis, 4T1 tumors abundantly expressed FcεRI; (3) 4T1 cells and some human breast cancer cell lines abundantly expressed FcεRI in vitro; (4) the function of FcεRI was limited to cytokine production only in some human breast cancer cell lines in vitro; and (5) conversely to cell models, primary human breast cancers probably do not express more FcεRI than primary non-cancerous breast tissue.