Over time, PBLs from both groups showed a decline in foci numbers, although it was still possible to visualize an average number of 1.46 ± 0.05 53BP1 foci/cell in PBLs from head and neck cancer patients and 1.97 ± 0.17 (~62%) 53BP1 foci/cell in PBLs from rectal cancer patients 24 h after the first fraction (1 ×; Fig. 3a). The gene discussed is TP53BP1; the disease is head and neck cancer.