CD44 and cancer: HA-drug bioconjugates, such as HA-Taxol, HA-CPT11, HA-Paclitaxel (PTX), and HA-polymer conjugates, can efficiently bind to CD44 overexpressing cancer cells and exert strong anti-proliferative activity on CD44 overexpressing cancer cells including human breast, colon, ovarian, gastric, breast, esophageal, and lung cancer cells as well as rat colon adenocarcinoma and colorectal cancer cells [188–190].