IDO1 and head and neck squamous cell carcinoma: IDO1 expression was low, but inducible upon IFNγ treatment of HNSCC cells. Upon treatment with 5‐FU, Gemcitabine and Cetuximab, IDO1 and additional genes of the KP (KYAT1, KYAT2 and KMO) were induced. Cyclin‐dependent kinase inhibitor Dinaciclib suppressed the KP, whilst conventional chemotherapeutics tend to activate the KP