DNA polymerase theta complexed with a double-stranded DNA (deoxyribonucleic acid) and an inhibitor. Molecular model of DNA polymerase theta (blue-green) complexed with a double-stranded DNA consisting of a DNA primer (red) and a DNA template (green), and the Z5X inhibitor C20.H16.F7.N3.O3 (not visible). DNA polymerase theta is a DNA damage response (DDR) protein and a promising drug target in BRCA1/2 mutant cancers.