Although we were not able to validate LIG4 with a clonogenic assay as an essential gene for radiation response as its knockout already negatively impacted clonogenic growth, our screen results support the importance of LIG4 in response to radiotherapy and suggests that targeting LIG4 or XRCC4 could have a radiosensitizing effect in HNSCC. Here, XRCC4 is linked to head and neck squamous cell carcinoma.