Objective: This prespecified exploratory analysis evaluated the association of gene expression signatures, tumor mutational burden (TMB), and multiplex immunohistochemistry (mIHC) tumor microenvironment-associated cell phenotypes with clinical outcomes of pembrolizumab in advanced recurrent ovarian cancer (ROC) from the phase II KEYNOTE-100 study., Methods: Pembrolizumab-treated patients with evaluable RNA-sequencing (n = 317), whole exome sequencing (n = 293), or select mIHC (n = 125) data were evaluated. The association between outcomes (objective response rate [ORR], progression-free survival [PFS], and overall survival [OS]) and gene expression signatures (T-cell-inflamed gene expression profile [Tcell inf GEP] and 10 non-Tcell inf GEP signatures), TMB, and prespecified mIHC cell phenotype densities as continuous variables was evaluated using logistic (ORR) and Cox proportional hazards regression (PFS; OS). One-sided p-values were calculated at prespecified α = 0.05 for Tcell inf GEP, TMB, and mIHC cell phenotypes and at α = 0.10 for non-Tcell inf GEP signatures; all but Tcell inf GEP and TMB were adjusted for multiplicity., Results: No evidence of associations between ORR and key axes of gene expression was observed. Negative associations were observed between outcomes and Tcell inf GEP-adjusted glycolysis (PFS, adjusted-p = 0.019; OS, adjusted-p = 0.085) and hypoxia (PFS, adjusted-p = 0.064) signatures. TMB as a continuous variable was not associated with outcomes (p > 0.05). Positive associations were observed between densities of myeloid cell phenotypes CD11c + and CD11c + /MHCII - /CD163 - /CD68 - in the tumor compartment and ORR (adjusted-p = 0.025 and 0.013, respectively)., Conclusions: This exploratory analysis in advanced ROC did not find evidence for associations between gene expression signatures and outcomes of pembrolizumab. mIHC analysis suggests CD11c + and CD11c + /MHCII - /CD163 - /CD68 - phenotypes representing myeloid cell populations may be associated with improved outcomes with pembrolizumab in advanced ROC., Clinical Trial Registration: ClinicalTrials.gov, NCT02674061., Competing Interests: Declaration of Competing Interest J.A. Ledermann reports receiving research grants from AstraZeneca and Merck/MSD; lecture fees from Clovis Oncology, AstraZeneca, Neopharm, GSK and MSD/Merck; and advisory board fees from AstraZeneca, GSK, Artios Pharma, Clovis Oncology, ImmunoGen, Mersana, Bristol Myers Squibb, Nuvation, Ellipses Pharma, VBL Therapeutics, Eisai, Regeneron, and Immagene, outside of the submitted work. R. Shapira-Frommer reports receiving support with medical writing for the submitted work from MSD; a research grant from MSD; consulting fees paid to her from MSD and Clovis Oncology; payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events paid to her from MSD, Bristol Myers Squibb, Roche, AstraZeneca, Sanofi, Medison Pharma, Neopharm, and Novartis; participation on a data safety monitoring board or advisory board for MSD (received personal fee), Novartis (received personal fee), and AstraZeneca (unpaid); and a role in the ENGOT early phase study group (unpaid), outside of the submitted work. A.D. Santin reports grants or contracts paid to his institution from Genentech, Immunomedics, Gilead, Merck, Boehringer Ingelheim, and Tesaro; consulting fees paid to him from Merck, Eisai, and R-Pharm US; and participation on a data safety monitoring board or advisory board for Merck, Eisai, and R-PHARM US, outside of the submitted work. A.S. Lisyanskaya reports no disclosures. S. Pignata reports receiving payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from MSD, GSK, Roche, AstraZeneca, and Clovis Oncology, outside of the submitted work. I. Vergote reports contracted research via KU Leuven to his institution from Oncoinvent AS; corporate-sponsored research to his institution from Amgen and Roche; consulting fees paid to him from Agenus, Akesobio, AstraZeneca, Bristol Myers Squibb, Deciphera Pharmaceuticals, Eisai, Elevar Therapeutics, Exelixis, Roche, Genmab, GSK, ImmunoGen, Jazz Pharmaceuticals, Karyopharm Therapeutics, Mersana, MSD, Novocure, Novartis, Oncoinvent, OncXerna, Regeneron, Sanofi, Seagen, Sotio, Verastem Oncology, and Zentalis; and travel support to himself from Karyopharm Therapeutics, Genmab, and Novocure, outside of the submitted work. F. Raspagliesi reports receiving grants or contracts from GSK, MSD, and AstraZeneca; payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing or educational events from GSK, MSD, and AstraZeneca; and support for attending meetings and/or travel from GSK, outside of the submitted work. G.S. Sonke reports payments to his institution for inclusion of trial subjects and medical writing support, all from MSD, for the submitted work; institutional research support from Agendia, AstraZeneca, Merck, Novartis, Roche, and Seagen; and consulting fees paid to his institution from Biovica, Novartis, and Seagen, outside of the submitted work. M. Birrer reports no disclosures. D.M. Provencher reports receiving payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing or educational events from AstraZeneca and GSK and participation on a data safety monitoring board or advisory board for GSK, outside of the submitted work. J. Sehouli reports receiving consulting fees from Roche, GSK, Tesaro, Novocure, Clovis Oncology, MSD, Merck, Pfizer, and Astra Zeneca; payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from Roche, GSK, Tesaro, Novocure, Clovis, MSD, Merck, Pfizer, Astra Zeneca, and Eisai; support for attending meetings and/or travel from Roche, GSK, Tesaro, and AstraZeneca; participation on a data safety monitoring board or advisory board for Roche, GSK, Tesaro, Novocure, Clovis Oncology, MSD, Merck, Pfizer, AstraZeneca, Eisai, and PharmaMar; and roles on/as the council of ESGO), president of NOGGO, president of PARSGO, speaker of the Ovarian Cancer Commission (AGO), and delegate to GCIG, outside of the submitted work. N. Colombo reports receiving medical writing support from MSD for the submitted work; grants or contracts paid to her from MSD, Roche, and GSK; consulting fees paid to her from MSD, Roche, GSK, and AstraZeneca; payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events to her from AstraZeneca, GSK, Novartis, Clovis Oncology, and MSD; support for attending meetings and/or travel from AstraZeneca, MSD, and GSK; participation on a data safety monitoring board or advisory board for AstraZeneca, Clovis Oncology, Eisai, GSK, ImmunoGen, Mersana, MSD/Merck, Nuvation Bio, OncXerna Therapeutics, Pfizer, Pieris, and Roche; and unpaid roles for ACTO Onlus and ESMO Guidelines Committee, outside of the submitted work. A. González-Martín reports receiving grants or contracts from Roche, GSK, and CCUN; consulting fees paid to him from Alkermes, Amgen, AstraZeneca, Clovis Oncology, Genmab, GSK, HederaDx, ImmunoGen, Illumina, Mersana, MSD, Novartis, Novocure, Oncoinvent, PharmaMar, Roche, SOTIO, Sutro Biopharma, Seagen, and Takeda; consulting fees paid to him from Alkermes, Amgen, AstraZeneca, Clovis Oncology, Genmab, GSK, HederaDx, ImmunoGen, Illumina, Mersana, MSD, Novartis, Novocure, Oncoinvent, PharmaMar, Roche, SOTIO, Sutro Biopharma, Seagen, and Takeda; payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing, or educational events paid to him from GSK, Clovis, AstraZeneca, MSD, Mersana, and Roche; support for attending meetings and/or travel paid to him from AstraZeneca/MSD and GSK; and unpaid roles as president of GEICO and ENGOT, outside of the submitted work. A. Oaknin reports grants or contracts paid to her institution from AbbVie Deutschland, Advaxis Inc., Aeterna Zentaris, Amgen, Aprea Therapeutics AB, Bristol Myers Squibb, Clovis Oncology Inc., Eisai, Roche, ImmunoGen, MSD de España S.A., Millennium Pharmaceuticals, PharmaMar SA, Regeneron Pharmaceuticals, and Tesaro; consulting fees paid to her from Agenus, AstraZeneca, Clovis Oncology, Corcept Therapeutics, Deciphera Pharmaceuticals, Eisai, EMD Serono, Roche, Genmab, GSK, ImmunoGen, Itheos, MSD de España, S.A., Mersana Therapeutics, Novocure, PharmaMar, prIME Oncology, Roche, Sattucklabs, Seagen, Sutro Biopharma, and Tesaro; payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from ESMO, Edizioni Minerva Medica SpA, and Doctaforum Servicios S.L; support for attending meetings and/or travel paid to her from AstraZeneca, PharmaMar, and Roche; and payment to her for participation on a data safety monitoring board or advisory board from Agenus, AstraZeneca, Clovis Oncology, Corcept Therapeutics, Deciphera Pharmaceuticals, Eisai, EMD Serono, Roche, Genmab, GSK, ImmunoGen, Itheos, MSD de España S.A., Mersana Therapeutics, Novocure, PharmaMar, prIME Oncology, Roche, Sattucklabs, Seagen, Sutro Biopharma, and Tesaro, outside of the submitted work. P. B. Ottevanger reports receiving support for manuscript writing and provision of study patients from MSD for the submitted work. V. Rudaitis reports no disclosures. J. Kobie is an employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, and has stock in Merck & Co., Inc., Rahway, NJ, USA. M. Nebozhyn is an employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, and has stock in Merck & Co., Inc., Rahway, NJ, USA, and reports a pending patent (WO 2020/167619) related to the application of angiogenesis and mMDSC gene expression-based biomarker of tumor response to PD-1 antagonists. M. Edmondson is an employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA. Y. Sun is an employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA and has stock in Merck & Co., Inc., Rahway, NJ, USA. R. Cristescu is an employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA and has stock in Merck & Co., Inc., Rahway, NJ, USA; and reports a pending patent (WO 2020/167619) related to the application of Angiogenesis and mMDSC gene expression-based biomarker of tumor response to PD-1 antagonists. P. Jelinic is an employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA. S.M. Keefe is an employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, and has stock in Merck & Co., Inc., Rahway, NJ, USA. U.A. Matulonis reports consulting fees paid to her from Merck, GSK, and AstraZeneca; payment made to her from Med Learning Group for her role on the committee on endometrial cancer, which involved creation of the entire lecture and slides; payment made to her for lectures, presentations, speakers bureaus, manuscript writing, or educational events from Research to Practice; payments made to her for participation on the advisory board for Allarity, NextCure, Trillium, Agenus, ImmunoGen, Novartis, Boehringer Ingelheim, Rivkin Foundation, Ovarian Cancer Research Alliance, Clearity Foundation, MorphoSys, and CureLab; and payments for participation on a data safety monitoring board for Alkermes and Symphogen, outside of the submitted work., (Copyright © 2023 Elsevier Inc. All rights reserved.)