Neoadjuvant versus adjuvant chemotherapy in locally advanced hormone receptor-positive, HER2-negative invasive lobular carcinoma: A retrospective cohort study based on the SEER database

This study compared survival outcomes between neoadjuvant chemotherapy (NACT) and adjuvant chemotherapy (ACT) in patients with locally advanced, hormone receptor-positive, HER2-negative invasive lobular carcinoma (ILC). We conducted a retrospective cohort study using Surveillance, Epidemiology, and End Results (SEER) data (2010-2020), including patients with stage II/III ILC who underwent both chemotherapy and surgery. Inverse probability of treatment weighting (IPTW) was used to balance baseline characteristics. Primary endpoints were breast cancer-specific survival (BCSS) and overall survival (OS). Among 7,496 eligible patients, 851 received NACT and 6,645 received ACT. After IPTW adjustment, ACT was associated with significantly improved BCSS (HR = 1.97, 95% CI: 1.59-2.45) and OS (HR = 1.97, 95% CI: 1.63-2.38) in stage III ILC. Younger patients (< 50 years) with stage II disease also showed a survival advantage with ACT. No significant differences were observed in older stage II patients. For locally advanced HR+/HER2 - ILC, adjuvant chemotherapy was associated with superior survival compared to neoadjuvant chemotherapy, particularly in stage III disease and younger stage II patients. However, these findings should be interpreted with caution given the study's retrospective nature and inherent limitations. Prospective studies are needed to confirm these observations and identify patient subgroups most likely to benefit from each treatment sequence.