Relapse-free survival and metastasis-free survival between patients with breast cancer receiving adjuvant or neoadjuvant therapy: A retrospective study in Iran.

Background: Breast cancer is the most common malignancy among women in Iran and worldwide. Although both neoadjuvant and adjuvant chemotherapies are widely used, their impact on relapse-free survival (RFS) and metastasis-free survival (MFS) in real-world settings remains unclear. This study aimed to compare RFS and MFS between neoadjuvant and adjuvant chemotherapy in breast cancer patients. Methods: A retrospective cohort study was conducted on patients who had received adjuvant or neoadjuvant therapy at Seyed Al-Shohada Hospital during July 2016 and July 2020. The cut-off date was July 202. Kaplan-Meier analysis and Cox regression models were used to evaluate RFS and MFS. To address potential confounding by indication due to non-randomized treatment assignment, inverse probability of treatment weighting (IPTW) was applied using propensity scores based on age, tumor grade, and molecular subtype. Results: Neoadjuvant therapy was significantly associated with increased relapse risk compared to adjuvant therapy in both multivariate (HR = 3.06, P = 0.030) and IPTW-weighted models (HR = 6.10, P = 0.002). No significant difference in MFS was observed between treatment groups. TNBC was identified as the strongest predictor of metastasis (HR = 6.45, P = 0.001). Subtype-specific analyses revealed better outcomes with adjuvant therapy in Luminal A and improved MFS/RFS with neoadjuvant therapy in TNBC. Conclusion: Adjuvant therapy was associated with better local disease control (RFS), while MFS was primarily influenced by tumor subtype. These findings highlighted the importance of subtype-tailored therapeutic strategies and supported the use of causal methods such as IPTW in observational oncology research.