This trial assessed the utility of applying tumor DNA sequencing to treatment selection for patients with advanced, refractory cancer and somatic mutations in one of four signaling pathways by comparing the efficacy of four study regimens that were either matched to the patient's aberrant pathway (experimental arm) or not matched to that pathway (control arm)., Materials and Methods: Adult patients with an actionable mutation of interest were randomly assigned 2:1 to receive either (1) a study regimen identified to target the aberrant pathway found in their tumor (veliparib with temozolomide or adavosertib with carboplatin [DNA repair pathway], everolimus [PI3K pathway], or trametinib [RAS/RAF/MEK pathway]), or (2) one of the same four regimens, but chosen from among those not targeting that pathway., Results: Among 49 patients treated in the experimental arm, the objective response rate was 2% (95% CI, 0% to 10.9%). One of 20 patients (5%) in the experimental trametinib cohort had a partial response. There were no responses in the other cohorts. Although patients and physicians were blinded to the sequencing and random assignment results, a higher pretreatment dropout rate was observed in the control arm (22%) compared with the experimental arm (6%; P = .038), suggesting that some patients may have had prior tumor mutation profiling performed that led to a lack of participation in the control arm., Conclusion: Further investigation, better annotation of predictive biomarkers, and the development of more effective agents are necessary to inform treatment decisions in an era of precision cancer medicine. Increasing prevalence of tumor mutation profiling and preference for targeted therapy make it difficult to use a randomized phase II design to evaluate targeted therapy efficacy in an advanced disease setting., Competing Interests: The following represents disclosure information provided by authors of this manuscript. All relationships are considered compensated unless otherwise noted. Relationships are self-held unless noted. I = Immediate Family Member, Inst = My Institution. Relationships may not relate to the subject matter of this manuscript. For more information about ASCO's conflict of interest policy, please refer to www.asco.org/rwc or ascopubs.org/po/author-center. Open Payments is a public database containing information reported by companies about payments made to US-licensed physicians (Open Payments). Shivaani KummarStock and Other Ownership Interests: PathomIQ, Arxeon Consulting or Advisory Role: Corvus Pharmaceuticals, MedTree, Nodus Therapeutics, Genentech, ShangPharma Innovation, Seattle Genetics, Bayer, Boehringer Ingelheim, Mundipharma EDO GMBH, Harbour BioMed, Cadila Pharmaceuticals Research Funding: Bristol Myers Squibb, Dynavax Technologies, Pfizer, Loxo, Corvus Pharmaceuticals, Plexxikon, Jounce Therapeutics, ADC Therapeutics, Advenchen Laboratories, Incyte, Taiho Pharmaceutical, Bayer, Astex Pharmaceuticals, Seattle Genetics, Amgen, Genome & Company Travel, Accommodations, Expenses: BayerNancy MoorePatents, Royalties, Other Intellectual Property: Nestle NutritionP. Mickey WilliamsResearch Funding: Illumina Patents, Royalties, Other Intellectual Property: I was a co-inventor of the DLBCL cell of origin patent recently filed by the NIHKanwal P. S. RaghavConsulting or Advisory Role: AstraZeneca, Bayer, Eisai, Daiichi SankyoFunda Meric-BernstamEmployment: MD Anderson Cancer Center Honoraria: Mayo Clinic, Rutgers Cancer Institute of New Jersey Consulting or Advisory Role: Genentech, Inflection Biosciences, Samsung Bioepis, Spectrum Pharmaceuticals, Aduro Biotech, OrigiMed, Xencor, Debiopharm Group, Mersana, Seattle Genetics, Silverback Therapeutics, Immunomedics, IBM, Roche, PACT Pharma, eFFECTOR Therapeutics, Jackson Laboratory for Genomic Medicine, Kolon Life Sciences, Parexel International, Pfizer, Tyra Biosciences, Zymeworks, Puma Biotechnology, Zentalis, Alkermes Speakers' Bureau: Chugai Pharma Research Funding: Novartis, AstraZeneca, Taiho Pharmaceutical, Genentech, Calithera Biosciences, Debiopharm Group, Bayer, Aileron Therapeutics, Puma Biotechnology, CytomX Therapeutics, Jounce Therapeutics, Zymeworks, Curis, Pfizer, eFFECTOR Therapeutics, Abbvie, Boehringer Ingelheim, Guardant Health, Daiichi Sankyo, GlaxoSmithKline, Seattle Genetics, Millennium Travel, Accommodations, Expenses: Taiho Pharmaceutical, Beth Israel Deaconess Medical CenterStephen LeongEmployment: Merck Sharp & Dohme Stock and Other Ownership Interests: Antares Pharmaceuticals, Spectrum Pharmaceuticals Consulting or Advisory Role: Bristol Myers Squibb Research Funding: Deciphera, Karyopharm Therapeutics, Bristol Myers Squibb, Lilly Travel, Accommodations, Expenses: Genentech/RocheSaiama WaqarResearch Funding: Spectrum Pharmaceuticals, Lilly, Pfizer, Genentech/Roche, Daiichi Sankyo, Newlink Genetics, EMD Serono, Puma Biotechnology, Novartis, Xcovery, Synermore Biologics, Celgene, Vertex, Bristol Myers Squibb, Stemcentrx, Hengrui Therapeutics, Checkpoint Therapeutics, Ignyta, AstraZeneca, ARIAD, Roche, MerckBiswajit DasResearch Funding: IlluminaChris KarlovichStock and Other Ownership Interests: Clovis Oncology Research Funding: Illumina Travel, Accommodations, Expenses: IlluminaChih-Jian LihEmployment: Exelixis Stock and Other Ownership Interests: ExelixisEric PolleyResearch Funding: GRAILRichard SimonConsulting or Advisory Role: AbbVie, Amgen, Janssen, Bristol Myers Squibb, Pfizer, Onco-Nano Travel, Accommodations, Expenses: Amgen No other potential conflicts of interest were reported., (© 2021 by American Society of Clinical Oncology.)