Objectives: Programmed cell death ligand 1 (PD-L1) is the most important immune checkpoint protein in immune defense against tumors. PD-1/PD-L1 inhibitors are considered an option in cancer treatments. The evaluation of PD-L1 immunohistochemical staining is used as a biomarker to determine the decision and response of the use ofthese inhibitory drugs. There is a wide variety of clones and platforms for the PD-L1 antibody, and each pathology department uses different clones and platforms which causes confusion. Therefore, in this study, we evaluated the immunohistochemical staining of different clones in the same tumor. Methods: Overall, 90 cases comprising 47 lung, 11 breast, 9 colon, 6 stomach, and 7 pancreatic carcinomas and 10 other tumors were included in the study. Of these, 43 specimens were obtained by resection, 40 by tru-cut biopsy, and 7 by endoscopic biopsy. Sections prepared from formalin-fixed paraffin-embedded blocks were evaluated immunohistochemically with SP142 and SP263 clones. Results: In this study, we observed positive staining in 48.8% (n=44) and negative staining in 51.2% (n=46) among all cancers with SP263 clone, and positive staining in 33.3% (n=30) and negative staining in 66.7% with SP142 clone as well. This study also showed that compared to SP263, SP142 clone stained tumor cells less in lung, colon, stomach, pancreatic, and other carcinomas. Conclusion: In this study, we found different staining percentages for SP263 and SP142 in the same tumor. Pathologists conducting immunohistochemical studies for PD-L1 should indicate the staining percentages of tumors and the antibody clone they used in the reports. Meanwhile, oncologists should keep in mind which clone was stained, and that selecting SP142 is less positive to correct patients who can receive appropriate immunotherapy. Keywords: Cancer, immunohistochemistry, staining, stomach.
Corresponding Author: Fatma Tokat