ObjectiveThis study aimed to investigate whether dexmedetomidine （Dex） alleviates stress-induced mammary tumor progression in mice by inhibiting the TLR4/NF‑κB signaling pathway， and to examine its effects on anxiety‑depression‑like behaviors and stress hormone levels. MethodsAn orthotopic EMT6 mammary tumor model was established in mice， and chronic mild stress （CMS） was applied to induce anxiety‑depression‑like states. The mice were divided into six groups： naive， tumor， CMS， CMS+tumor， CMS+tumor+Dex， and CMS+tumor+Vehicle groups. Behavioral changes were evaluated using the open field test and tail suspension test. Plasma stress hormone levels were measured by high‑performance liquid chromatography. Western blot and RT‑qPCR were performed to detect the expression of TLR4， p‑NF‑κB p65， p‑IκBα， and inflammatory cytokines （IL‑6， IL‑1β， TNF‑α） in tumor tissues. In vitro， EMT6 cells were treated with cortisol to mimic the stress-related microenvironment， and the effects of Dex on the TLR4/NF‑κB pathway were assessed by CCK‑8， Western blot， and RT-qPCR. ResultsTumor‑bearing mice exhibited significant anxiety‑depression‑like behaviors （P＜0.05）， along with markedly elevated plasma levels of norepinephrine， epinephrine， and cortisol （P＜0.05）. Chronic stress further aggravated these behavioral abnormalities and promoted tumor growth （P＜0.05）. Dexmedetomidine intervention significantly improved anxiety‑depression‑like behaviors （P＜0.05） and lowered peripheral stress hormone levels （P＜0.05） in stress‑exposed tumor‑bearing mice. In vitro experiments demonstrated that cortisol treatment activated the TLR4/NF‑κB pathway （P＜0.001） and upregulated the expression of inflammatory cytokines （P＜0.05 in EMT6 cells， whereas dexmedetomidine effectively suppressed this activation （P＜0.001）. In the in vivo model， dexmedetomidine treatment downregulated the expression of TLR4， p‑NF‑κB p65， p‑IκBα， and pro‑inflammatory cytokines in tumor tissues （P＜0.001） and significantly inhibited tumor growth （P＜0.05）. ConclusionDexmedetomidine inhibits the TLR4/NF‑κB signaling pathway， alleviates stress‑induced inflammatory responses， improves anxiety- and depression‑ like behaviors， reduces stress hormone levels， and suppresses mammary tumor progression. These findings provide an experimental basis for understanding anxiety- and depression- associated breast tumor progression and suggest that Dexmedetomidine and the TLR4/NF-κB pathway may serve as potential therapeutic targets.