CME articleHistopathologic PD-L1 Tumor Expression and Prognostic Significance in Nonmelanoma Skin Cancers: A Systematic ReviewLehmer, Larisa MD*; Choi, Franchesca RPh, MD†,‡; Kraus, Christina MD§; Shiu, Jessica MD PhD§; de Feraudy, Sebastien MD, PhD¶; Elsensohn, Ashley MD, MPH‖Author Information *Resident, Department of Dermatology, University of California Irvine, Irvine, CA; †Research Fellow and Resident, School of Medicine, University of California Irvine, Irvine, CA; ‡Research Fellow and Resident, Department of Pathology, Kaohsiung Medical University, Kaohsiung, Taiwan; §Assistant Professor, Department of Dermatology, University of California Irvine, Irvine, CA; ¶Dermatopathologist, Kaiser Regional Dermatopathology Service, Kaiser Permanente, San Francisco, CA; and ‖Fellow, Dermatopathology Section, Geisinger Medical Center, Danville, PA. Correspondence: Ashley Elsensohn, MD, MPH, Dermatopathology Fellow, Geisinger Medical Center, Laboratory Medicine, 100 N Academy Avenue MC 19-20, Danville, PA 17822 (e-mail: [email protected]). All authors and staff in a position to control the content of this CME activity and their spouses/life partners (if any) have disclosed that they have no financial relationships with, or financial interests in, any commercial organizations relevant to this educational activity. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.amjdermatopathology.com). The American Journal of Dermatopathology: May 2021 - Volume 43 - Issue 5 - p 321-330 doi: 10.1097/DAD.0000000000001772 Buy SDC CME Test Metrics Abstract PD-L1 and PD-1 inhibitors are being increasingly used to treat a variety of nonmelanoma skin cancers (NMSCs). This systematic review summarizes PD-L1 expression in NMSCs and determines its use for prognosis using targeted immunotherapy. A primary search of peer-reviewed English-language medical literature was conducted for studies on PD-L1 tumor expression in biopsied or excised NMSCs. Fifty-nine articles met criteria for inclusion. PD-L1 expression in advanced NMSCs ranged from 22%–89% for basal cell carcinomas, 42%–50% for Merkel cell carcinomas, and 26%–100% for squamous cell carcinomas. Study limitations included clone heterogeneity across studies, complicating comparison of PD-L1 expression. Differences were also noted in the selection of tumor reactivity threshold. We conclude that there is insufficient evidence to determine the prognostic significance of PD-L1 expression in NMSCs as a whole, but this remains a promising area. More investigation into the role of tumor PD-L1 as a biomarker for predicting clinical response to PD-L1 and PD-1 inhibitors in NMSCs is needed. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.