Tumor biomarker testing can help inform treatment decisions for ovarian cancer patients. This information is discovered by testing the tumor for biomarkers, such as PD-L1, homologous recombination deficiency (HRD), tumor mutation burden (TMB), and microsatellite instability (MSI) and using next generation sequencing to identify genomic alterations in more than 300 genes. 
At diagnosis, testing for germline and somatic BRCA1/2 mutations as well as HRD are recommended to inform decisions about the use of PARP inhibitors in the maintenance setting. At recurrence, a comprehensive genomic analysis is particularly helpful for patients with less common ovarian cancer histology types and is recommended in the NCCN guidelines. In some cases, there is an approved drug for patients with specific tumor biomarkers (e.g, MSI or high TMB for immune checkpoint inhibitors). In other cases, tumor biomarker testing can inform choice of clinical trials which require specific tumor genomic alterations for enrollment.