For example, in PARPi resistance, reversion of BRCA1, BRCA2, PALB2, RAD51C, or RAD51D occur because the continued fitness of tumour cells is not dependent upon the continued dysfunction of these genes; tumour cells with reversions are clearly no longer reliant or dependent upon defective HR for their survival (Fig. 1B). The gene discussed is BRCA1; the disease is neoplasm.