PARP1 (poly(ADP-ribose) polymerase 1) is a nuclear protein involved in the regulation of various biological processes including apoptosis, DNA repair for the maintenance of genome integrity, epigenetic marking of chromatin, assembly of higher-order chromatin structures, transcriptional activation, differentiation, proliferation, and cell cycle. Particularly, due to its decisive role in several DNA repair pathways, the inhibition of PARP1 has emerged as a prominent therapeutic option in cancer treatment, by improving the efficiency of chemotherapeutics or radiation therapy. © 2020 Atlas of Genetics and Cytogenetics in Oncology and Haematology.