Poor Outcome of Hormone Receptor–Positive Breast Cancer at Very Young Age Is Due to Tamoxifen Resistance: Nationwide Survival Data in Korea—A Report From the Korean Breast Cancer Society

PURPOSE: Breast cancer in very young women (age .05). CONCLUSION: Younger patients (age < 35) showed worse prognosis than older patients (age, 35 to 50 years) only in the hormone receptor-unknown or hormone receptor-positive subgroups. Adjuvant tamoxifen therapy might provide less survival benefit when added to chemotherapy in very young breast cancer patients.