Abstract: A method and composition is disclosed for the prophylactic treatment of cancer tumor cells contained in a host body having a natural immunological system and wherein the tumor cells have a protective surface resistant to the immunological system, to prevent or at least reduce further development of the tumor cells comprising; introducing a solution of a proenzyme and a pharmaceutically acceptable carrier into the host body adjacent the tumor cells, the solution having a concentration of the proenzyme at least in excess of the proenzymes produced by the host body in the area of the tumor cells, and contacting the tumor cells with the proenzyme whereby the proenzyme is converted to its active form which reacts with the tumor cell surface to sufficiently decompose the surface to permit the natural immunological system to prevent or reduce development of tumor cells.