Benefit of adjuvant chemotherapy in luminal A-like early breast cancer in women aged 40 years or younger: results of a national multi-institutional study

Background: Young age is an established adverse prognostic factor in early-stage breast cancer (eBC), irrespective of molecular subtype or stage at diagnosis. However, the benefit of adjuvant chemotherapy (aCT) in patients aged ≤ 40 years with luminal A-like BC remains unclear. This study evaluates the impact of aCT on clinical outcomes in this population. Methods: We conducted a retrospective analysis of a multicenter cohort comprising 23,134 eBC patients treated between 1990 and 2014. Eligible patients were aged ≤ 40 years with luminal A-like tumors (SBR grade 1 or 2, endocrine receptor (ER)-positive, HER2-negative). The impact of aCT on disease-free survival (DFS) and overall survival (OS) was assessed using multivariate Cox regression, adjusting for key prognostic factors. Results: A total of 464 patients met the inclusion criteria, of whom 295 received aCT. Patients who underwent aCT had more unfavorable prognostic features, including younger age, larger tumors, higher grade, lymphovascular invasion, and nodal involvement. Multivariate analysis demonstrated a significant OS benefit with aCT (HR = 0.21, 95% CI [0.05–0.84], p = 0.028 ), whereas DFS improvement did not reach statistical significance (HR = 0.57, 95% CI [0.27–1.22], p = 0.147 ). Independent predictors of OS included tumor size, macroscopic lymph node involvement, and radiotherapy, while only tumor size was significantly associated with DFS. Conclusions: In patients aged ≤ 40 years with luminal A-like eBC, aCT confers a significant OS benefit. Although a trend toward improved DFS was observed, statistical significance was not achieved. Further studies are warranted to refine patient selection criteria and optimize therapeutic strategies for this subgroup.