Purpose: To update recommendations on appropriate use of breast cancer biomarker assay results to guide adjuvant endocrine and chemotherapy decisions in early-stage breast cancer., Methods: An updated literature search identified randomized clinical trials and prospective-retrospective studies published from January 2016 to October 2021. Outcomes of interest included overall survival and disease-free or recurrence-free survival. Expert Panel members used informal consensus to develop evidence-based recommendations., Results: The search identified 24 studies informing the evidence base., Recommendations: Clinicians may use Onco type DX, MammaPrint, Breast Cancer Index (BCI), and EndoPredict to guide adjuvant endocrine and chemotherapy in patients who are postmenopausal or age > 50 years with early-stage estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative (ER+ and HER2-) breast cancer that is node-negative or with 1-3 positive nodes. Prosigna and BCI may be used in postmenopausal patients with node-negative ER+ and HER2- breast cancer. In premenopausal patients, clinicians may use Onco type in patients with node-negative ER+ and HER2- breast cancer. Current data suggest that premenopausal patients with 1-3 positive nodes benefit from chemotherapy regardless of genomic assay result. There are no data on use of genomic tests to guide adjuvant chemotherapy in patients with ≥ 4 positive nodes. Ki67 combined with other parameters or immunohistochemistry 4 score may be used in postmenopausal patients without access to genomic tests to guide adjuvant therapy decisions. BCI may be offered to patients with 0-3 positive nodes who received 5 years of endocrine therapy without evidence of recurrence to guide decisions about extended endocrine therapy. None of the assays are recommended for treatment guidance in individuals with HER2-positive or triple-negative breast cancer. Treatment decisions should also consider disease stage, comorbidities, and patient preferences.Additional information is available at www.asco.org/breast-cancer-guidelines., Competing Interests: Fabrice AndreStock and Other Ownership Interests: PegacsyResearch Funding: AstraZeneca (Inst), Novartis (Inst), Pfizer (Inst), Lilly (Inst), Roche (Inst), Daiichi (Inst).Travel, Accommodations, Expenses: Novartis, Roche, GlaxoSmithKline, AstraZeneca Nofisat IsmailaEmployment: GlaxoSmithKline (I)Stock and Other Ownership Interests: GlaxoSmithKline (I) Kimberly H. AllisonConsulting or Advisory Role: MammotomeExpert Testimony: Kaiser Permanente William E. BarlowResearch Funding: Merck (Inst), AstraZeneca (Inst). Deborah E. CollyarHonoraria: PfizerConsulting or Advisory Role: Parexel, MaxisIT, Kinnate BiopharmaTravel, Accommodations, Expenses: Parexel Senthil DamodaranResearch Funding: EMD Serono (Inst), Guardant Health (Inst), Taiho Pharmaceutical (Inst), Novartis (Inst), Sermonix Pharmaceuticals (Inst) N. Lynn HenryResearch Funding: Blue Note Therapeutics (Inst)Open Payments Link: https://openpaymentsdata.cms.gov/physician/27894/summary Komal JhaveriConsulting or Advisory Role: Novartis, Pfizer, AstraZeneca, Jounce Therapeutics, Synthon, Intellisphere, Bristol Myers Squibb, Genentech, AbbVie, Lilly, BluePrint Medicines, Seattle Genetics, Daiichi Sankyo, Biotheranostics, SunPharma Pvt Ltd, Taiho Oncology, SanofiResearch Funding: Novartis (Inst), Genentech (Inst), Debiopharm Group (Inst), ADC Therapeutics (Inst), Pfizer (Inst), Novita Pharmaceuticals (Inst), Clovis Oncology (Inst), Lilly (Inst), Zymeworks (Inst), Immunomedics (Inst), Puma Biotechnology (Inst), VelosBio/Merck (Inst), AstraZeneca (Inst)Travel, Accommodations, Expenses: Taiho Pharmaceutical, Jounce Therapeutics, Pfizer, AstraZeneca, Intellisphere Kevin KalinskyStock and Other Ownership Interests: Array BioPharma, Pfizer, GRAILConsulting or Advisory Role: bioTheranostics, Lilly, Pfizer, Novartis, Eisai, AstraZeneca, Genentech/Roche, Immunomedics, Ipsen, Merck, Seattle Genetics, Cyclacel, Oncosec, 4D Pharma, Daiichi Sankyo/Astra Zeneca, Puma BiotechnologySpeakers' Bureau: LillyResearch Funding: Incyte (Inst), Novartis (Inst), Genentech/Roche (Inst), Lilly (Inst), Pfizer (Inst), Calithera Biosciences (Inst), Immunomedics (Inst), Acetylon Pharmaceuticals (Inst), Seattle Genetics (Inst), Amgen (Inst), Zeno Pharmaceuticals (Inst), CytomX Therapeutics (Inst)Travel, Accommodations, Expenses: Lilly, AstraZeneca, PfizerOther Relationship: Immunomedics, Genentech Nicole M. KudererEmployment: Self-employedConsulting or Advisory Role: Janssen, BeyondSpring Pharmaceuticals, Invitae, Bristol Myers Squibb, Samsung Bioepis, G1 Therapeutics, Sandoz-Novartis, BeyondSpring Pharmaceuticals, Teva, MerckResearch Funding: AmgenTravel, Accommodations, Expenses: Janssen, Mylan, Agendia, Bayer, Spectrum Pharmaceuticals Anna LitvakConsulting or Advisory Role: Bristol Myers Squibb, bioTheranostics Erica L. MayerConsulting or Advisory Role: Lilly, Novartis, AstraZeneca, Gilead SciencesResearch Funding: Pfizer (Inst) Lajos PusztaiHonoraria: bioTheranostics, Natera, OncoCyte, AthenexConsulting or Advisory Role: H3 Biomedicine, Merck, Novartis, Seattle Genetics, Syndax, AstraZeneca, Roche/Genentech, Bristol Myers Squibb, Clovis Oncology, Immunomedics, Eisai, Almac Diagnostics, PfizerResearch Funding: Merck (Inst), Genentech (Inst), Seattle Genetics (Inst), AstraZeneca (Inst), Bristol Myers Squibb (Inst), Pfizer (Inst)Travel, Accommodations, Expenses: AstraZenecaUncompensated Relationships: NanoString Technologies, Foundation MedicineOpen Payments Link: https://openpaymentsdata.cms.gov/physician/110878 Antonio C. WolffThis author is an Associate Editor for Journal of Clinical Oncology. Journal policy recused the author from having any role in the peer review of this manuscript.Consulting or Advisory Role: Ionis PharmaceuticalsPatents, Royalties, Other Intellectual Property: Antonio Wolff has been named as inventor on one or more issued patents or pending patent applications relating to methylation in breast cancer, and has assigned his rights to JHU, and participates in a royalty sharing agreement with JHUOpen Payments Link: https://openpaymentsdata.cms.gov/physician/357301/summary Vered StearnsConsulting or Advisory Role: NovartisResearch Funding: AbbVie (Inst), Pfizer (Inst), Novartis (Inst), Puma Biotechnology (Inst), Biocept (Inst)Other Relationship: Immunomedics, AstraZenecaNo other potential conflicts of interest were reported. Fabrice AndreStock and Other Ownership Interests: PegacsyResearch Funding: AstraZeneca (Inst), Novartis (Inst), Pfizer (Inst), Lilly (Inst), Roche (Inst), Daiichi (Inst).Travel, Accommodations, Expenses: Novartis, Roche, GlaxoSmithKline, AstraZeneca Nofisat IsmailaEmployment: GlaxoSmithKline (I)Stock and Other Ownership Interests: GlaxoSmithKline (I) Kimberly H. AllisonConsulting or Advisory Role: MammotomeExpert Testimony: Kaiser Permanente William E. BarlowResearch Funding: Merck (Inst), AstraZeneca (Inst). Deborah E. CollyarHonoraria: PfizerConsulting or Advisory Role: Parexel, MaxisIT, Kinnate BiopharmaTravel, Accommodations, Expenses: Parexel Senthil DamodaranResearch Funding: EMD Serono (Inst), Guardant Health (Inst), Taiho Pharmaceutical (Inst), Novartis (Inst), Sermonix Pharmaceuticals (Inst) N. Lynn HenryResearch Funding: Blue Note Therapeutics (Inst)Open Payments Link: https://openpaymentsdata.cms.gov/physician/27894/summary Komal JhaveriConsulting or Advisory Role: Novartis, Pfizer, AstraZeneca, Jounce Therapeutics, Synthon, Intellisphere, Bristol Myers Squibb, Genentech, AbbVie, Lilly, BluePrint Medicines, Seattle Genetics, Daiichi Sankyo, Biotheranostics, SunPharma Pvt Ltd, Taiho Oncology, SanofiResearch Funding: Novartis (Inst), Genentech (Inst), Debiopharm Group (Inst), ADC Therapeutics (Inst), Pfizer (Inst), Novita Pharmaceuticals (Inst), Clovis Oncology (Inst), Lilly (Inst), Zymeworks (Inst), Immunomedics (Inst), Puma Biotechnology (Inst), VelosBio/Merck (Inst), AstraZeneca (Inst)Travel, Accommodations, Expenses: Taiho Pharmaceutical, Jounce Therapeutics, Pfizer, AstraZeneca, Intellisphere Kevin KalinskyStock and Other Ownership Interests: Array BioPharma, Pfizer, GRAILConsulting or Advisory Role: bioTheranostics, Lilly, Pfizer, Novartis, Eisai, AstraZeneca, Genentech/Roche, Immunomedics, Ipsen, Merck, Seattle Genetics, Cyclacel, Oncosec, 4D Pharma, Daiichi Sankyo/Astra Zeneca, Puma BiotechnologySpeakers' Bureau: LillyResearch Funding: Incyte (Inst), Novartis (Inst), Genentech/Roche (Inst), Lilly (Inst), Pfizer (Inst), Calithera Biosciences (Inst), Immunomedics (Inst), Acetylon Pharmaceuticals (Inst), Seattle Genetics (Inst), Amgen (Inst), Zeno Pharmaceuticals (Inst), CytomX Therapeutics (Inst)Travel, Accommodations, Expenses: Lilly, AstraZeneca, PfizerOther Relationship: Immunomedics, Genentech Nicole M. KudererEmployment: Self-employedConsulting or Advisory Role: Janssen, BeyondSpring Pharmaceuticals, Invitae, Bristol Myers Squibb, Samsung Bioepis, G1 Therapeutics, Sandoz-Novartis, BeyondSpring Pharmaceuticals, Teva, MerckResearch Funding: AmgenTravel, Accommodations, Expenses: Janssen, Mylan, Agendia, Bayer, Spectrum Pharmaceuticals Anna LitvakConsulting or Advisory Role: Bristol Myers Squibb, bioTheranostics Erica L. MayerConsulting or Advisory Role: Lilly, Novartis, AstraZeneca, Gilead SciencesResearch Funding: Pfizer (Inst) Lajos PusztaiHonoraria: bioTheranostics, Natera, OncoCyte, AthenexConsulting or Advisory Role: H3 Biomedicine, Merck, Novartis, Seattle Genetics, Syndax, AstraZeneca, Roche/Genentech, Bristol Myers Squibb, Clovis Oncology, Immunomedics, Eisai, Almac Diagnostics, PfizerResearch Funding: Merck (Inst), Genentech (Inst), Seattle Genetics (Inst), AstraZeneca (Inst), Bristol Myers Squibb (Inst), Pfizer (Inst)Travel, Accommodations, Expenses: AstraZenecaUncompensated Relationships: NanoString Technologies, Foundation MedicineOpen Payments Link: https://openpaymentsdata.cms.gov/physician/110878 Antonio C. WolffThis author is an Associate Editor for Journal of Clinical Oncology. Journal policy recused the author from having any role in the peer review of this manuscript.Consulting or Advisory Role: Ionis PharmaceuticalsPatents, Royalties, Other Intellectual Property: Antonio Wolff has been named as inventor on one or more issued patents or pending patent applications relating to methylation in breast cancer, and has assigned his rights to JHU, and participates in a royalty sharing agreement with JHUOpen Payments Link: https://openpaymentsdata.cms.gov/physician/357301/summary Vered StearnsConsulting or Advisory Role: NovartisResearch Funding: AbbVie (Inst), Pfizer (Inst), Novartis (Inst), Puma Biotechnology (Inst), Biocept (Inst)Other Relationship: Immunomedics, AstraZenecaNo other potential conflicts of interest were reported.