Briefly, for immunohistochemistry, 4 μm sections were cut from the formalin-fixed paraffin embedded (FFPE) blocks of the cancer patient collected at the time of cytoreductive surgery and 79 additional high grade serous ovarian carcinoma from a recently described tissue microarray ovarian cancer cohort (15 (link)), and stained with the following antibodies according to the manufacturers’ instructions. CD8 (clone 144B, ready to use, DAKO, Carpinteria, CA), CD4 (clone 1F6, 1:40 dilution, Vector, Burlingame CA), CD3 (clone 2GV6, Ventana, Tucson, AZ), CD56 (clone 1B6, 1:200 dilution, Vector, Burlingame CA), CD68 (clone PG-M1, ready to use, DAKO, Carpinteria, CA), CD20 (clone L26, 1:200 dilution, DAKO, Carpinteria, CA), TIA-1 (clone TIA1, ready to use, Biocare, Concord, CA), CK7 (clone OVTL, Dako, Carpinteria, CA) and PD-L1 (clone E1L3N, 1:200 Cell Signaling, Danvers, MA). For antigen retrieval, the sections were pre-treated at low pH for PD-L1 and CD8, CD4, CD20, CD56 and CD68. PD-L1 antibody and membranous immunoreactivity was assessed semi-quantitatively in tumor cells as follows: <1% staining was considered negative, staining in 1–50% of tumor cells was scored as focal, and >50% staining was scored as diffusely positive.