Whilst we are unaware of any other studies investigating the influence of MK-8776 or MK-1775 in combination with high-LET PBT in HNSCC or any other tumour types, one study has been performed utilising the Chk1 inhibitor UCN-01 in combination with carbon ions, which have considerably higher LET than PBT. This evidence concerns the gene CHEK1 and head and neck squamous cell carcinoma.