Euphorbia hirta L. is traditionally used to treat tumors and has demonstrated anticancer effects. This study evaluated the phytochemical composition, toxicity, and antitumor activity of saline extract (SE) from E. hirta leaves in mice. Phytochemical analysis included thin layer chromatography, high-performance liquid chromatography, and quantification of phenols, flavonoids, and proteins. Acute toxicity (2000 mg/kg) assessed mortality, hematological, biochemical, histological parameters, water/feed intake, and body weight. Genotoxicity was evaluated via comet and micronucleus assays. Antitumor activity was tested in vitro and in vivo on sarcoma 180. SE contained 107.3 mg GAE/g phenolics and 22.9 mg QE/g flavonoids; the presence of gallic and ellagic acids was detected. Protein concentration was 12.16 mg/mL with lectin activity present. No mortality, organ damage, or genotoxic effects occurred in toxicity tests. SE demonstrated in vitro cytotoxicity against sarcoma cells (IC₅₀: 10 µg/mL). In vivo, SE (50–200 mg/kg) reduced tumor weight by 70.2–72.3%. SE modulated IL-2, IL-4, IL-6, IL-17, IFN-γ, and TNF-α in tumor environment. Tumors showed inflammatory infiltrate, necrosis, and fibrosis after treatment. These findings position the extract as a promising candidate for further development as a safe, plant-based antitumor agent.