Subtype-Dependent Relationship Between Young Age at Diagnosis and Breast Cancer Survival

PURPOSE: Young women are at increased risk for developing more aggressive subtypes of breast cancer. Although previous studies have shown a higher risk of breast cancer recurrence and death among young women with early-stage breast cancer, they have not adequately addressed the role of tumor subtype in outcomes. METHODS: We examined data from women with newly diagnosed stage I to III breast cancer presenting to one of eight National Comprehensive Cancer Network centers between January 2000 and December 2007. Multivariable Cox proportional hazards models were used to assess the relationship between age and breast cancer-specific survival. RESULTS: A total of 17,575 women with stage I to III breast cancer were eligible for analysis, among whom 1,916 were ≤ 40 years of age at diagnosis. Median follow-up time was 6.4 years. In a multivariable Cox proportional hazards model controlling for sociodemographic, disease, and treatment characteristics, women ≤ 40 years of age at diagnosis had greater breast cancer mortality (hazard ratio HR, 1.4; 95% CI, 1.2 to 1.7). In stratified analyses, age ≤ 40 years was associated with statistically significant increases in risk of breast cancer death among women with luminal A (HR, 2.1; 95% CI, 1.4 to 3.2) and luminal B (HR 1.4; 95% CI, 1.1 to 1.9) tumors, with borderline significance among women with triple-negative tumors (HR, 1.4; 95% CI, 1.0 to 1.8) but not among those with human epidermal growth factor receptor 2 subtypes (HR, 1.2; 95% CI, 0.8 to 1.9). In an additional model controlling for detection method, young age was associated with significantly increased risk of breast cancer death only among women with luminal A tumors. CONCLUSION: The effect of age on survival of women with early breast cancer seems to vary by breast cancer subtype. Young age seems to be particularly prognostic in women with luminal breast cancers.