a therapeutic composition comprising a chemical conjugatge including a first moiety , other than an immunoglobulin or fragment thereof , such as epidermal growth factor , which preferentially binds to a tumor cell , and is internalized by the cell , and a second moiety linked to the first moiety , and comprising a biodegradable polymeric carrier , such as polyglutamic acid , to which one or more cytotoxic molecules , for instance , daunomycin , are attached . the degradation of the carrier by intracellular enzymes releases a cytotoxic agent , resulting in selective destruction of the tumor cells .