CD274 and ovarian serous adenocarcinoma: The overall response rate to pembrolizumab among PD-L1+ advanced metastatic ovarian cancer patients is only 11.5% (11), and the percentage of PD-L1+ cases of high grade serous ovarian cancer is only 57.4%, and it is 0%–26.7% in other histologic subtypes of ovarian cancer (12).