Influence of the loading dose on the demonstration of abnormal tryptophan metabolism by cancer patients

Abstract

The incidence of abnormal tryptophan metabolism in early or advanced breast cancer, or carcinoma of the cervix, has been studied using 2-g or 5-g l-tryptophan oral test loads. Although more than one third of early breast cancer patients had elevated excretions of tryptophan metabolites after a 5-g load, the levels after 2-g did not differ from those of normal female controls. It is suggested that the larger dose is necessary to demonstrate an effect of minor changes in hormone activity on the tryptophan-nicotinic acid ribonucleotide pathway in early breast cancer, as it is in normal women. The cervical cancer group excreted a significantly higher level of 3-hydroxy-kynurenine tlian controls after a 2-g load, but the total amount of this dose excreted as hydroxykynurenine, xanthurenic acid and 3-hydroxyanthranilic acid was slightly elevated in only three of these 28 cancer patients. Tryptophan metabolism after a 5-g load is usually normal in carcinoma of the cervix. Elevated excretions of tryptophan metabolites after either 2-g or 5-g loads were observed frequently in advanced breast cancer. Carcinoma of the bronchus has been studied only with the 2-g dose; 40% had abnormal metabolism.