**5.2 Epigenetics and precision medicine**

The heterogeneity of ovarian cancer is such that no two tumors are alike, however, tumors expressing similar genetic profiles, have been shown to respond to agents targeting their specific genetics. Recent clinical trials indicate that ovarian cancer patients with homologous recombination deficiency, for example, respond well to PARP inhibition [79, 80]. Newer epigenetic therapies like BET inhibitors, have the ability enhance PARP inhibition [69]. Another clinical challenge in ovarian cancer is the *ARID1A* mutation. Ovarian cancers with this mutation are associated with late-stage disease at diagnosis and early recurrence [81]. Roughly 50 percent of clear cell carcinomas, which are notoriously chemoresistant, harbor this mutation. In one murine model, the HDACi vorinostat was found to be highly effective against ARID1A mutated ovarian cancer [81]. Thus, epigenetics may help further precision medicine and the targeting of actionable mutations.
