Previously, IDO1‐positive P815 murine mastocytoma clones demonstrated metabolic interactions between the tumour and the microenvironment, which led to cell‐typing analysis that could be distilled into three general states: growth of tumour cells, suppression of effector functions and metabolism of tumour‐associated T cells, and promotion of a tolerogenic microenvironment.30 Here, IDO1 is linked to neoplasm.