Since SLFN11 promotes sensitivity to DNA damaging agents that interfere with DNA replication fork progression [60,61,62], possibly including evofosfamide [54], reduced expression of SLFN11 in PDX tumours relative to clinical tumours suggests the PDX tumours could potentially under-predict the clinical activity of evofosfamide in HNSCC. Here, SLFN11 is linked to head and neck squamous cell carcinoma.