Anti-interleukin-8 (IL-8) treatment significantly decreased breast cancer cells (BCC) dissemination induced by breast adipocytes (BAd). Prior injections, breast pre-adipocytes were differentiated for 12 days and estrogen receptor positive (ER+) BCC were cultured ± β-estradiol (E2) 1 nM for 48 h. All BCC were labeled with 4 µg/ml Fast DiI™ oil red dye. Cells were injected ± anti-IL-8, anti-VEGF, or isotype control at 0.1 mg/ml ± E2 1 nM into the perivitelline space of 2 days old zebrafish embryos, which expressed enhanced green fluorescent protein in endothelial cells. (A) MCF-7 cells were injected alone or in combination with 50% BAd ± E2 1 nM. BCC dissemination was evaluated 3 days post-injections, n = 18–27 in each group. (B) T47D cells were injected alone or in combination with 50% BAd ± E2 1 nM. BCC dissemination was evaluated 3 days post-injections, n = 16–28 in each group. (C) MDA-MB-231 cells were injected alone or in combination with 50% BAd. BCC dissemination was evaluated 3 days post-injections, n = 14–18 in each group. (D) MCF-7, T47D, and MDA-MB-231 cells were cultured alone or in combination with 50% breast pre-adipocytes in vitro during 24 h, and migration of cells was determined as described in Section “Materials and Methods,” n = 6 in each group. BV = blood vessels. Arrows indicate disseminated BCC. Results are presented as mean ± SEM and analyzed by Student’s t-test, *p < 0.05, **p < 0.01, ***p < 0.001. Data are representative of at least two independent experiments.