The pivotal study that provides the most substantial evidence of the KP involvement in cancer is the study by Muller et al. They demonstrated that combination therapy of a chemotherapeutic drug and an IDO1 inhibitor, 1-methyl-D-tryptophan (1MT), reduced the tumour size by 30% in a HER2-enriched mouse model. The gene discussed is ERBB2; the disease is neoplasm.