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 < 35 years) is uncommon and poorly understood. We sought to evaluate the prognosis and treatment response of these patients compared with women ages 35 to 50 years. Patients and Methods We analyzed data from 9,885 breast cancer patients age <= 50 years who were part of the Korean Breast Cancer Society registration program between 1992 and 2001. The overall survival (OS) and breast cancer-specific survival (BCSS) were compared between age groups. Results One thousand four hundred forty-four patients (14.6%) were younger than age 35 and 8,441 (85.4%) patients were between 35 and 50 years of age. Younger patients had significantly higher T-stage and higher lymph node positivity and lower hormone receptor expression than older patients. Younger patients had a greater probability of death than older patients, regardless of tumor size or lymph node status. The survival difference was significant for patients with positive or unknown hormone receptor status (P < .0001), but not for patients with negative hormone receptor status. In a multivariate analysis, the interaction term of young age and hormone receptor positivity was significant for OS and BCSS with a hazard ratio for OS of 2.13 (95% CI, 1.52 to 2.98). The significant survival benefit from adjuvant hormone therapy after chemotherapy observed in older patients (hazard ratio for OS, 0.61; 95% CI, 0.47 to 0.79; P = .001) could not be seen in younger patients (P >.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.