BRCA1 and neoplasm: Moreover, tumour cells with deficient homologous recombination (HR) repair mechanisms, including BRCA1/2-mutated tumours and BRCA-like tumours (tumours with HR-related gene mutations except for BRCA1/2 mutations—i.e., BRCAness), are more sensitive to PARPi due to the "synthetic lethality effect" 26, 27.