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The incidence of breast cancer in ≤ 40 yr-old women (YWBC) has been steadily increasing in recent decades. Although this group of patients represents less than 10 % of all newly diagnosed BC cases it encompasses a significant burden of disease. Usually underrepresented in clinical trials, YWBCs are also characterized by late diagnoses and poorly differentiated, aggressive-subtype disease, partly explaining its poor prognosis along with a high recurrence risk, and high mortality rates. On the other hand, YWBC treatment poses unique challenges such as preservation of fertility, and long-term toxicity and adverse events. Herein, we summarize the current evidence in hormone receptor-positive YWBC including specific risk factors, clinicopathologic and genomic features, and available evidence on response to chemotherapy and endocrine therapy. Overall, we advocate for a more comprehensive multidisciplinary healthcare model to improve the outcomes and the quality of life of this subset of younger patients., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: [BW reports travel expenses from Astra Zeneca and BMS. IGF has declared honoraria for presentations from Novartis, Daiichi Sankyo, Esteve, GSK; and travel expenses from Novartis, Gilead, Daiichi Sankyo, Lilly, and BMS. OMS has declared travel expenses and consulting fees from Roche and Reveal, and speaker fees from Eisai, Daiichi-Sankyo, and Novartis. FS reports honoraria and travel expenses from Novartis, Gilead and Daiichy Sankyo, and advisory role for Pfizer. CS has received honorary for lectures from Roche, Novartis, Astra Zeneca, Pfizer, consulting/advisory role for Roche, Novartis, Pfizer, MSD and Astra Zeneca, and travel expenses from Roche and Pfizer. MM reports grants from Novartis, Breast Cancer Research Foundation- AACR, Breast Cancer Now Career Catalyst, during the study and advisors from Novartis, Roche, Pfizer and Lilly, outside of the submitted work. FBM reports patent application (PCT/EP2022/086493, PCT/EP2023/060810, EP23382703 and EP23383369). AP has declared personal honoraria from Pfizer, Novartis, Roche, MSD Oncology, Lilly and Daiichi Sankyo, travel, accommodations, and expenses paid by Daiichi Sankyo, research funding from Nanostring Technologies, Roche and Novartis, consulting/advisory role for Nanostring Technologies, Roche, Novartis, Pfizer, Oncolytics Biotech, Amgen, Lilly, MSD, PUMA and Daiichi Sankyo, Inc. outside the submitted work. MVL has declared honoraria for presentations from Novartis, Roche, Pfizer, and Daichii, and travel expenses from Roche and Pfizer. Additionally, she has participated on a Data Safety Monitoring Board or Advisory Board for Novartis and Roche.], (Copyright © 2024 Elsevier Ltd. All rights reserved.)