TDO2 and colorectal cancer: TDO2 has been identified in colorectal cancer to activate the Kyn-AhR pathway, increase glycolysis to drive metabolic cancer cell growth and CXCL5 secretion to recruit macrophages into the tumor microenvironment (31).We hypothesize that in HPV-positive OPSCC, E7 transcriptional regulation of HIF-1α inhibits TDO2 expression, thereby inhibiting the glycolytic pathway, resulting in a better prognosis and better treatment responsiveness in HPV-positive OPSCC.