High-grade serous ovarian cancers (HGSOCs) which are BRCA mutant/HRR deficient show increased CD8+ TILs, elevated levels of PD-1/PD-L1 expression and greater neoantigen load, indicating that certain OC subtypes may benefit from PD-1/PD-L1 blockade. Here, CD274 is linked to ovarian serous adenocarcinoma.