Although PARPi-based therapy is standard of care for patients with germline BRCA1/2 mutations including breast and ovarian cancer, resistance has been observed in these patients, where reversion mutations of BRCA1 or BRCA2 are a well-documented resistance mechanism53,54 and can be assessed through profiling of circulating free DNA (cfDNA)55. Here, BRCA1 is linked to ovarian cancer.