Background: The incidence of young Asian women with breast cancer has been increasing but these patients are underrepresented in global data. We analyzed the epidemiology and outcomes of the young Asian patients with breast cancer in different subtypes with clinically unmet need. Methods: Female patients of age 20 years or older diagnosed with early breast cancer of stage I, II, or III from the prospective cohort of the Asian Breast Cancer Cooperative Group (ABCCG) were analyzed. For comparison, data of patients with early breast cancer from Surveillance, Epidemiology, and End Results Program (SEER) cancer registry was used. The patients were divided into three age groups: young (below 40 years), alleged premenopausal mid-age (40-49 years), and alleged postmenopausal elderly (50 years and older). Multivariable Cox proportional-hazard models for survivals were adjusted with age, subtypes consisting of hormone receptor (HR) and human epithelial growth factor receptor 2 (HER2) status, histologic grade, T stage, nodal status, and countries. Patients diagnosed in 2000–2010 were censored at 6 years for comparability with SEER database. Results: Total 45,021 patients with breast cancer from Asian countries, 496,332 of SEER Whites and 18,279 from SEER non-Whites were included. The median age at diagnosis was younger in Asians compared to SEER Whites and non-Whites (51, 62, 58 years, respectively). Among subtypes, HR-positive and HER2-negative breast cancer was more frequent among SEER Whites and SEER non-Whites, compared to Asians (75.89%, 73.38% vs. 65.75%, respectively). In the young group, HR-positive and HER2-negative breast cancer was prevalent in Asians and SEER non-Whites, compared to SEER Whites (61.2% and 59.8% vs. 54.7%, respectively). In the elderly group, the proportion of HR-positive breast cancer increased in SEER Whites, while that of triple-negative breast cancer (TNBC) increased in Asians. Elderly group showed the worst survival in all subtypes and in all populations. In Asian population, the mid-age group of the patients with HR-positive and HER2-negative breast cancer showed significantly superior overall survival (OS) than the young group (6 year OS 96.6% vs. 94.4%; hazard ratio 0.62, 95% confidence interval 0.50-0.76; p<0.001). Similarly, young patients in SEER Whites also showed early decline of survival curve compared those in mid-age group (89.1% vs. 94.0%, p<0.001), while young patients of SEER non-Whites showed equivalent prognosis to those in mid-age group (92.4% vs. 95.0%, p=0.118). Conclusions: Young Asian breast cancer patients diagnosed with HR-positive and HER2-negative subtypes, but not HER2-positive or TNBC subtypes, are more likely to have worse survival outcomes than those in mid-age. Further studies on young patients with breast cancer are needed for tailored treatments among different subtypes and ethnic groups.