Not all cancer therapeutic strategies known to date are adequate for all cancer types and patients. Many of them are followed by a high rate of side effects and complications. L-Tryptophan metabolism plays a key role in organism development. As well as in the occurrence and development of tumors. By degrading certain amino acids, tumor growth can be limited while maintaining the body ?s normal nutritional requirements. L-tryptophan depletion bioreactor is described as a possible new therapeutic strategy of cancer therapy. L-tryptophan is an essential amino acid, which has been recognized as an important cancer nutrient and its removal can lead to destruction of the tumor. Normal human cells or cancer cells cannot synthesize L-tryptophan and therefor tumor resistance is unlikely to develop. L-tryptophan is also a constituent for different bio-molecules such as Serotonin, Melatonin, and is needed for other synthesis processes in the cell growth. A column, which contained tryptophan side-chain oxidase (TSO) as a bioreactor, was integrated in a therapeutic plasma exchange unit, and tested it in different animals and cancer cell lines. Breast cancer, medulloblastoma, and hepatocellular carcinoma showed greatest efficacy of L-tryptophan degrading. TSO is developed to treat cancer diseases successfully, and has low side effects. A combination of L-tryptophan depletion with all available cancer therapies is possible.