Most solid tumours are difficult to target with nanoparticles owing to the presence of a vascular barrier. Now, researchers have successfully delivered localized chemotherapy using a fucoidan-based nanoparticle with a high affinity for the cell-surface adhesion protein P-selectin, a molecule expressed on the vascular barrier of a wide variety of human cancers. Researchers used this nanoparticle to deliver doxorubicin to tumours in mice with metastatic melanoma or breast cancer: treatment with fucoidan-doxorubicin nanoparticles resulted in a significant increase in overall survival of these mice, relative to mice treated with non-fucoidan doxorubicin-conjugated nanoparticles, or conventionally delivered chemotherapy. These data indicate a need for further testing of P-selectin targeted therapies.