Conflict of Interest Disclosures: Dr Schram reported receiving trial funding from Pfizer during the conduct of the study; receiving trial funding to her institution from AstraZeneca, ArQule, BeiGene/Springworks, Black Diamond Therapeutics, Elevation Oncology, Kura, Eli Lilly and Co, Merus, Northern Biologics, Pfizer, PMV Pharma, Relay Therapeutics, Repare Therapeutics, Revolution Medicines, and Surface Oncology and having a consulting or advisory role with Roche; PharmaMar, AstraZeneca, Merck and Co (Kenilworth, New Jersey), Clovis Oncology, Tesaro; GlaxoSmithKline, Novartis, Pfizer, Takeda, BIOCAD, Immunogen, Mersana, Eisai, and Oncxerna outside the submitted work. Dr Colombo reported receiving personal fees from Pfizer during the conduct of the study and receiving personal fees from AstraZeneca, Clovis, Roche, Merck Sharpe & Dohme, GlaxoSmithKline, Immunogen, Mersana, Eisai, Oncxerna, Novartis, and Nuvation Bio outside the submitted work. Dr Arrowsmith reported that their institution, Tennessee Oncology, has a research relationship with Sarah Cannon Research Institute, which is compensated for research by study sponsors including the sponsor of this study. Dr Narayan reported receiving grants from Pfizer during the conduct of the study and receiving grants and personal fees from Pfizer, Janssen Pharmaceuticals, and Merck; receiving personal fees from Regenergon, Amgen, Myovant Sciences, and Exelixis; receiving grants from Bristol Myers Squibb and Tmunity Therapeutics outside the submitted work. Dr Yonemori reported receiving grants from Pfizer during the conduct of the study and receiving honoraria from Pfizer, Eisai, Takeda, Eli Lilly and Co, Chugai, Fuji Film Pharma, Merck Sharp & Dohme, Ono, Boeringer Ingerlheim, AstraZeneca, Daiichi Sankyo, OncXerna, Genmab, and Novartis; having a consulting or advisory role with Novartis, Eisai, AstraZeneca, Chugai, Takeda, Genmab, and OncXerna; and receiving research support to institution from Merck Sharpe & Dohme, Daiichi-Sankyo, AstraZeneca, Taiho, Pfizer, Novartis, Takeda, Chugai, Ono, Sanofi, Seattle Genetics, Eisai, Eli Lilly and Co, Genmab, Boeringer Ingelheim, Kyowa Hakko Kirin, Nihon Kayaku, and Haihe outside the submitted work. Dr Scambia reported receiving research support from Merck & Co; having a consulting or advisory role with Tesaro, Johnson & Johnson, and Clovis Oncology Italy outside the submitted work. Dr Zelnak reported receiving personal fees from AstraZeneca, Gilead, Seattle Genetics, Puma Biotechnology, Novartis, and Pfizer outside the submitted work. Dr Bauer reported receiving personal fees for consulting from Guadrant Health, Loxo, Exelixis, Blueprint Medicines, Foundation Medicine, AstraZeneca, Pfizer, Eli Lilly and Co, Bayer, and Bristol Myers Squibb; receiving personal fees for consulting to the institution from Ignyta, Moderna Therapeutics, and Pfizer; being on the speakers’ bureau for Bayer, Bristol Myers Squibb, and Eli Lilly and Co; receiving research support to the institution from Mirati Therapeutics, MedImmune, AbbVie, AstraZeneca, Leap Therapeutics, MabVax, Stemline Therapeutics, Merck, Eli Lilly and Co, GlaxoSmithKline, Novartis, Pfizer, Genentech/Roche, Deciphera, Merrimack, Immunogen, Millennium, Ignyta, Calithera Biosciences, Kolltan Pharmaceuticals, Principa Biopharma, Peleton, Immunocore, Aileron Therapeutics, Bristol Myers Squibb, Amgen, Moderna Therapeutics, Sanofi, Boehringer Ingelheim, Astellas Pharma, Five Prime Therapeutics, Jacobio, Top Alliance BioScience, Loxo, Janssen Pharmaceuticals, Clovis Oncology, Takeda, Karyopharm Therapeutics, Onyx, Phosplatin Therapeutics, Foundation Medicine, and ARMO BioSciences; and receiving travel grants from Astellas Pharma, AstraZeneca, Celgene, Clovis Oncology, Genentech, Eli Lilly and Co, Merck (Darmstadt, Germany), Novartis, Pharmacyclics, Sysmex, and Pfizer outside the submitted work. Dr Ulahannan reported receiving research support to the institution from Pfizer during the conduct of the study; having a consulting or advisory role with Array, Incyte, Bayer, Syros, and Eisai and receiving research support to the institution from AbbVie, ArQule, AstraZeneca, Atreca, Boehringer Ingelheim, Bristol Myers Squibb, Celgene, Ciclomed, Evelo Biosciences, G1 Therapeutics, GlaxoSmithKline, IGM Biosciences, Incyte, Isofol, Klus Pharma, Macrogenics, Merck & Co (Kenilworth, New Jersey), Mersana Therapeutics, OncoMed Pharmaceuticals, Regeneron, Revolution Medicines, Synermore Biologics, Takeda, Tarveda, Tesaro, Tempest, and Vigeo outside the submitted work. Dr Colleoni reported receiving grants from Roche outside the submitted work. Dr Aftimos reported receiving travel grants from Amgen, Merck and Co (Kenilworth, New Jersey), Daiichi Sankyo, Pfizer, Merck Sharpe & Dohme, and Roche; receiving honoraria from Synthon, Amgen, Novartis, and Gilead; receiving grants from Roche; receiving personal fees from Roche, Novartis, Macrogenics, Gilead, Amcure, Radius, Menarini, Servier, G1 Therapeutics, Boehringer Ingelheim, Deloitte, and Synthon outside the submitted work. Dr Telli reported receiving personal fees from Pfizer during the conduct of the study and receiving grants from AstraZeneca, Bayer, Pfizer, Genentech, Merck (Darmstadt, Germany), OncoSec, Tesaro, EMD Serrono, Vertex, Biothera, Calithera, Hummingbird Biosciences, and AbbVie; receiving personal fees from OncoSec, Gilead, Guardant, Natera, Genentech, RefleXion, Sanofi, G1 Therapeutics, Immunomedics, Novartis, Blueprint Medicines, Eli Lilly and Co, AbbVie, Merck, and Daiichi Sankyo outside the submitted work. Dr Domchek reported receiving personal fees from AstraZeneca and GlaxoSmithKline during the conduct of the study and research support to the institution from AstraZeneca and Pfizer and having a consulting or advisory role with AstraZeneca and Clovis outside the submitted work. Dr Galsky reported receiving personal fees from Pfizer during the conduct of the study and receiving research support to the institution from Janssen Oncology; Dendreon; Novartis; Bristol Myers Squibb; Merck (Darmstadt, Germany); AstraZeneca; and Genentech/Roche; receiving fees for consulting or advisory roles to the institution from BioMotiv, Janssen Pharmaceuticals, Dendreon, Merck (Darmstadt, Germany), GlaxoSmithKline, Eli Lilly and Co, Astellas Pharma, Genentech, Bristol Myers Squibb, Novartis, Pfizer, AstraZeneca, Seattle Genetics, Incyte, Aileron Therapeutics, Dracen, Inovio Pharmaceuticals, NuMab, Dragonfly Therapeutics, Basilea, Urogen Pharmaceuticals, and Gilead; and receiving personal fees from Incyte, Bristol Myers Squibb, Merck, Genentech, AstraZeneca, EMD Serono, Seattle Genetics, Janssen Pharmaceuticals, Numab, Dragonfly, GlaxoSmithKline, Basilea, Urogen, Rappta, and Alligator; and owning stock in Rappta outside the submitted work; in addition, Dr Galsky has a patent for Compositions and Methods for Treating Cancer, Overcoming PD-1/PD-L1 Blockade Resistance, and Determining Resistance to Checkpoint Inhibitor Treatment pending. Ms Hoyle and Dr Chappey reported being employed by and owning stock in Pfizer during the conduct of the study and outside the submitted work. Dr Stewart reported being employed by Pfizer during the conduct of the study and owning shares in Pfizer and AstraZeneca outside the submitted work. Dr Blake-Haskins reported being employed by and owning stock in Pfizer during the conduct of the study and outside the submitted work. Dr Yap reported serving as medical director of the Institute for Applied Cancer Science, which has a commercial interest in DNA damage repair response and other inhibitors; receiving research support from and serving as a consultant or advisor to Merck (Darmstadt, Germany) and Pfizer; receiving research support to the institution from Artios, AstraZeneca, Bayer, Clovis, Constellation, Cyteir, Eli Lilly and Co, Forbius, F-Star, GlaxoSmithKline, Genentech, ImmuneSensor, Ipsen, Jounce, Karyopharm, Kyowa, Novartis, Ribon Therapeutics, Regeneron, Repare, Sanofi, Scholar Rock, Seattle Genetics, Tesaro, and Vertex; having a consulting or advisory role with Almac, Aduro, AstraZeneca, Atrin, Axiom, Axiom, Bayer, Bristol Myers Squibb, Calithera, Clovis, Cybrexa, F-Star, Guidepoint, Ignyta, I-Mab, Janssen, Repare, Roche, Rubius, Schrodinger, Seagen, Varian, and Zai Lab outside the submitted work. No other disclosures were reported.