Patients with Early-Stage and Estrogen Receptor-Negative Breast Cancers: Young Age Does Link to Poor Outcomes

Purpose: This study aimed to evaluate whether young adult breast cancer patients have poor outcomes independent of established prognostic factors and analyze differences in prognosis between younger and older patients stratified by tumor subtype. Methods: Of 10,950 breast cancer patients treated at West China Hospital between 1998 and 2017, 741 younger patients (<35 years) and 3705 older patients (≥35 years) were enrolled in this study after applying exclusion criteria and matching adjusted for the diagnosis year. Breast cancer-specific survival (BCSS) and disease-free survival (DFS) were analyzed between the two groups before and after propensity score matching (PSM) as well as in different subgroups. Results: We identified 11 parameters (all P < 0.05) that differed between the two groups. Cox regression analysis hazard ratios (HR) for BCSS and DFS in younger patients were 1.604 (95% CI, 1.327 - 1.938; P < 0.001) and 1.425 (95% CI, 1.234 - 1.645; P < 0.001) with reference to the older group. After balancing the differences in baseline characteristics between the two groups by PSM, the HRs for BCSS and DFS of younger patients decreased; however, the differences remained significant (HR for BCSS = 1.328 [95% CI, 1.038 - 1.698; P = 0.024] and HR for DFS = 1.301 [95% CI, 1.077 - 1.572; P = 0.006]). When stratified by tumor subtype, younger patients with T1, N0, tumor stage I, G3, estrogen receptor (ER)-negative, progesterone receptor (PR)-negative, and Ki67 ≥ 14% had a poor BCSS; in addition, patients with T1, N1, tumor stages I and II, G3, ER-negative, PR-negative, and triple-negative had a poorer DFS than older patients. Conclusion: Young age was an independent prognostic factor for BCSS and DFS in breast cancer patients. The increased risk of relapse was most pronounced in early-stage breast cancer, especially in patients with ER-negative disease.