Wang W, et al. - Researchers evaluated the value of serum circSETDB1—a tumor-promoting circular RNAs (circRNAs) generated from the SET domain bifurcated histone lysine methyltransferase 1 (SETDB1), known to be upregulated in serous ovarian cancer (SOC)—as a biomarker for detecting SOC progression, in predicting relapse, and in estimating the effectiveness of SOC treatment. Serum circSETDB1 levels in 60 SOC patients (18 primary chemoresistance, 42 primary chemosensitive) and 60 healthy volunteers were assessed. Among SOC patients, they observed a positive correlation of higher levels of circSETDB1 with advanced clinical stage, lymph node metastasis of SOC patients. Notably, primary chemoresistance patients displayed significantly increased serum levels of circSETDB1. Shorter progression-free survival time was evident for patients with higher levels of circSETDB1. In addition, serum circSETDB1 enabled distinguishing patients with SOC from healthy volunteers as well as patients with primary chemoresistance from those with primary chemosensitivity in diagnostic value analyses. Data thereby support the value of serum circSETDB1 as a novel non-invasive biomarker for identifying SOC progression and predicting response to chemotherapy and relapse in high-grade serous ovarian cancer.