Second locoregional recurrence (LRR) in hormone receptor (HR)+/HER2- breast cancer (BC).

Abstract

e12537 Background: Evidence regarding the treatment and prognosis of patients with HR+/HER2- BC who experience a second consecutive, ipsilateral LRR remains limited. Methods: We analyzed treatment patterns and clinical outcomes of patients (pts) with HR+/HER2- BC who experienced a second consecutive, ipsilateral LRR, after a prior radical surgery and/or radiation therapy, with or without systemic treatment, and underwent surgery (study baseline) at the European Institute of Oncology (Milan) from Jan 2001 to Sep 2025 (cohort study). Patients with bilateral invasive BC, contralateral invasive recurrence, a non-invasive ipsilateral event before baseline, or a tumor clinical subtype switch were excluded. Endpoints included invasive breast cancer-survival (IBCFS) and distant recurrence-free survival (DRFS). Results: A total of 111 pts were included. The median age at study baseline was 61 years (IQR: 52-68), 77% were postmenopausal. The second LRR occurred in the residual breast parenchyma in 44% of pts, in locoregional lymph nodes in 23%, on the mastectomy scar or chest wall in 31%, and at multiple sites in 2%. An endocrine-resistant recurrence according to ESMO guidelines was observed in 69% of pts. ‘Adjuvant’ chemotherapy was administered in 14% of pts, and 5% received a CDK4/6 inhibitor. Endocrine therapy consisted predominantly of aromatase inhibitors (82%), with a switch from nonsteroidal to steroidal agents in 69% of these patients; fulvestrant was prescribed in 14%, tamoxifen in 2%, and no endocrine therapy in 2%. At a median follow-up of 6.3 years, 58 IBCFS and 37 DRFS events were reported. The median IBCFS was 6.8 years (95%CI: 5.0-8.6) and DRFS 13.5 years (95%CI: 6.3-20.7). A longer median DRFS was reported in pts with endocrine-sensitive LRR (not reached [NR] vs. 7.6 years in case of endocrine-sensitive LRR; p = .027) and in pts with LRR in breast tissue vs. those with lymph nodal or chest wall recurrence (NR vs. 9.0 vs. 5.5 years; p = .018). Conclusions: In this analysis, pts with a second consecutive HR+HER2- LRR who have endocrine-sensitive, intraparenchymal breast disease had favorable outcomes without chemotherapy. Those with endocrine-resistant disease or chest wall/lymph node recurrence had poorer outcomes and may warrant treatment intensification.