Current ovarian cancer treatment regimens can be aggressive, and push the outer limits of tolerability. This study demonstrates that negatively charged nanoparticles localize selectively at ovarian cancer metastases (not in healthy tissue) when they are administered into the abdomen. We show that the injected nanoparticles accumulate specifically in tumor-associated macrophages, making this targeted treatment approach especially profitable for existing immunotherapies targeting this cell population. This finding is exciting, because when the nanoparticles are pre-loaded with therapeutics, the off-target distribution of the drug should be drastically reduced. This would minimize the negative side-effects experienced by patients, and improve their quality of life while undergoing cancer treatment.