Obesity increases the risk and mortality of breast cancer through dysregulated secretion of proinflammatory cytokines and tumor adipokines that induce an inflammatory breast microenvironment. Resistin is an adipokine secreted by adipocytes, immune cells, and predominantly macrophages, which contributes to cancer progression, but its molecular mechanism in cancer is not completely described. In this study, we analyzed the relationship of resistin on breast cancer prognosis and tumor progression and the effect in vitro of resistin on p38 and ERK1/2 activation in breast cancer cell lines. By bioinformatic analysis, we found that resistin is overexpressed in the basal subtype triple-negative breast cancer and is related to poor prognosis. In addition, we demonstrated a positive correlation between RETN and MAPK3 expression in basal triple-negative breast cancer. Importantly, we found amplifications of the RETN gene in at least 20 % of metastatic samples from patients with breast cancer. Most samples with RETN amplifications metastasized to bone and showed high expression of IL-8 (CXCL8) and IL-6 (IL6). Finally, resistin could be considered a prognostic marker for basal triple-negative breast cancer, and we also proposed the possibility that resistin-induced cell migration involves the activation of MAPK in breast cancer cells.