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 < or = 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.