CLINICAL TRIAL Different prognosis of young breast cancer patients in their 20s and 30s depending on subtype: a nationwide study from the Korean Breast Cancer Society Jai Min Ryu 1 • Jonghan Yu 1 • Seung Il Kim 2 • Ku Sang Kim 3 • Hyeong-Gon Moon 4 • Jung Eun Choi 5 • Joon Jeong 6 • Kyung Do Byun 7 • Seok Jin Nam 1 • Jeong Eon Lee 1 • Se Kyung Lee 1 • Seok Won Kim 1 Received: 31 July 2017 / Accepted: 17 August 2017 Ó Springer Science+Business Media, LLC 2017 Abstract Purpose Numerous studies have demonstrated that breast cancer in young women (BCY) has unfavorable prognostic features and more unfavorable subtypes. However, few studies have evaluated the effect of subtype disparities on breast cancer prognosis by age, especially for BCY. We analyzed breast cancer mortality stratified by tumor sub- type according to age among patients younger than 50 years. Methods Data from the Korean Breast Cancer Society Registry for patients diagnosed with invasive breast cancer when aged less than 50 years between 2003 and 2010 were reviewed retrospectively. Results We identified 30,793 patients with breast cancer who were eligible for analysis. Of these, 793 (2.6%) were aged 20–29 and 8926 (28.8%) were aged 30–39. Median follow-up duration was 84 months. Mean age was 42.4 years. Patients in their 20s were more likely to have cancer of advanced stage and higher nuclear grade, present with lymphovascular invasion, and have unfavorable sub- types. Patients in the 20s group showed worse prognosis. In multivariate analysis for overall survival (OS), the hazard ratio (HR) for patients in the 20s group was higher than that for the 30s and 40s groups, and patients with triple-nega- tive breast cancer (TNBC) showed higher HR than patients with HER-2 or luminal subtype (all p \ 0.0001). When stratified by subtype, luminal subtype showed significantly worse prognosis in the 20s group than the 30s and 40s groups, whereas HER-2 and TNBC subtypes showed no significant difference. Conclusion Patients in their 20s with breast cancer had unfavorable characteristics and worse prognosis than patients in their 30s and 40s. When stratified by tumor subtype, patients in their 20s with luminal subtype of breast cancer showed worse prognosis than older patients, whereas HER-2 and TNBC subtypes showed no significant differences. Keywords Breast neoplasms Á Young women Á Prognosis Á Intrinsic subtype Introduction Breast cancer is one of the most common cancers and a leading cause of death among women worldwide. Numer- ous studies have demonstrated that breast cancer in young women (BCY) has unfavorable prognostic features. These Jai Min Ryu and Jonghan Yu have contributed equally to this work. & Seok Won Kim surgeon69@gmail.com 1 Division of Breast Surgery, Department of Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, 5th floor Breast-endocrine, Irwon-ro 81, Gangnam-gu, Seoul 06351, South Korea 2 Department of Surgery, Yonsei University College of Medicine, Seoul, South Korea 3 Breast-Thyroid Center, Ulsan City Hospital Group, Ulsan City Hospital, Ulsan, South Korea 4 Department of Surgery, Seoul National University College of Medicine, Seoul, South Korea 5 Department of Surgery, Yeungnam University Medical Center, Daegu, South Korea 6 Department of Surgery, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, South Korea 7 Breast Center, Dong-A University Hospital, Busan, South Korea 123 Breast Cancer Res Treat DOI 10.1007/s10549-017-4472-5