To expand our knowledge on DNA damage, we investigated PBLs of patients with head and neck cancer after RT and RCT using TEM, before and 0.1, 0.5, and 24 h after the first fraction, by quantifying pKu70 dimers and 53BP1 clusters in euchromatin and heterochromatin of 50 nuclear sections per sample. The gene discussed is TP53BP1; the disease is head and neck cancer.