USP1 and neoplasm: Down-regulation of the de-ubiquitylating enzyme USP1 (ubiquitin specific peptidase 1) in BRCA1-deficient cells leads to replication fork destabilisation in a synthetic lethal manner and may be another strategy to address PARPi resistance in HRR deficient tumour cells that have undergone stabilisation of the DNA replication fork [145,146].