Abstract: A composition for treating cancer is provided. The composition is a hexosaminidase covalently attached to a cancer cell targeting ligand and improves selectively of the hexosaminidase for tumor cells. In certain embodiments, the hexosaminidase is alternately chitinase (N-acetyl-glucosaminohydrolase), chitosanase, or N-acetyl-hexosaminidase and the targeting ligand is either a monoclonal antibody, an antibody fragment immunospecific to a tumor cell or cancer cell antigen, epidermal growth factor (EGF), fibroblast growth factor (FGF), transferrin, or folic acid. Also provided is a method for treating cancerous tumors comprising administering the composition to a patient that has a cancerous tumor.