While IL-2 biphasic (160) finding, i.e., it can promote immunity and suppress tumorigenesis in early tumor stages, but in mid- to late-tumor stages, IL-2 signaling promotes 5-hydroxytryptophan (5-HTP) production via the STAT5-TPH1 pathway, leading to CD8+ T-cell depletion. This evidence concerns the gene TPH1 and neoplasm.