Prognostic Significance of Young Age (<35 Years) by Subtype Based on ER, PR, and HER2 Status in Breast Cancer: A Nationwide Registry-Based Study

Young age is regarded as an adverse prognostic factor in patients with breast cancer, especially in those with a hormone receptor (HR)-positive tumor. We investigated the prognostic significance of an age of < 35 years stratified by molecular subtype based on HR and HER2. Two large databases of Korean breast cancer patients, which included nationwide registry data, were analyzed. In an analysis of 2,474 patients from the single institution, an age of < 35 years was found to be an independent predictor of recurrence in patients with HR+/HER2- (hazard ratio 1.87; 95% confidence interval [CI]: 1.11-3.14; P = 0.018), HR+/HER2+ (hazard ratio 3.09; 95% CI: 1.19-8.03; P = 0.020), and HR-/HER2+ (hazard ratio 2.01; 95% CI: 1.03-3.92; P = 0.040) subtypes, but not in those with the HR-/HER2- (triple-negative, TN) subtype (hazard ratio 1.08; 95% CI: 0.60-1.95; P = 0.802). The results of an analysis of nationwide database data on 31,672 patients also showed that an age of < 35 years significantly predicted poor cancer-specific survival in patients with HR+/HER2- (hazard ratio 3.40; 95% CI: 2.41-4.82; P < 0.001), HR+/HER2+ (hazard ratio 1.96; 95% CI: 1.23-3.12; P = 0.005), and HR-/HER2+ (hazard ratio 1.65; 95% CI: 1.07-2.52; P = 0.022) subtypes, but again not in those with the TN subtype (hazard ratio 1.21; 95% CI: 0.88-1.67; P = 0.240). The prognostic significance of young age was found to depend on molecular subtype. An age of < 35 years was a poor prognosticator in patients with the HR+/HER2-, HR+/HER2+, and HR-/HER2+ subtypes, but not in those with the TN subtype.