Parp inhibitors and haematological malignancies—friend or foe?

Since their introduction several years ago, poly (ADP-ribose) polymerase (PARP) inhibi-tors (PARPi) have become the standard of care for breast and gynaecological cancers with BRCA gene mutations. Given that PARPi act by exploiting defective DNA repair mechanisms within tu-mour cells, they should be ideally suited to combatting haematological malignancies where these pathways are notoriously defective, even though BRCA mutations are rare. To date, despite prom-ising results in vitro, few clinical trials in humans for haematological malignancies have been per-formed, and additional investigation is required. Paradoxically, secondary haematological malignancies have arisen in patients after treatment with PARPi, raising concerns about their potential use as therapies for any blood or bone marrow-related disorders. Here, we provide a comprehensive review of the biological, pre-clinical, and clinical evidence for and against treating individual haematological malignancies with approved and experimental PARPi. We conclude that the prom-ise of effective treatment still exists, but remains limited by the lack of investigation into useful biomarkers unique to these malignancies.