The most common strategies for NP tumor-targeting are (1) targeting NPs to immune cells and using the immune cells as NP carriers to indirectly target tumor cells, (2) functionalization with monoclonal antibodies to directly target unique or overexpressed antigens on the surface of tumor cells, and (3) functionalization with ligands/receptors against tumor-expressed receptors/ligands, such as hyaluronic acid (HA) to target CD44, often highly expressed on cancer cells [200,201]. The gene discussed is CD44; the disease is cancer.