This has, for example, been suggested for impaired activation of ATM itself or impaired activity of the ATM-orchestrated DDR for the enhanced radiation sensitivity of HPV-positive HNSCC [43, 44] or for inactivating ATM mutations for some exceptional tumor responses to radiotherapy [45] and may not be assessable by immunohistochemical protein quantification. Here, ATM is linked to head and neck squamous cell carcinoma.