Reversion mutations in HRR genes such as BRCA1, BRCA2, RAD51C, RAD51D, and PALB2 have been observed in ovarian cancer patients who developed PARP inhibitor resistance [39], and the genomic analysis of sequential cfDNA from plasma samples might allow clinicians to follow these genes along with treatment in order to anticipate which patients might have developed resistance. The gene discussed is PALB2; the disease is ovarian cancer.