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.