Clinical impact of lobular carcinoma in situ in patients undergoing breast-conserving surgery: risk of contralateral breast cancer without increased ipsilateral recurrence

BACKGROUND: Lobular carcinoma in situ (LCIS) increases breast cancer risk, but its clinical significance when diagnosed with invasive breast cancer remains unclear. This study evaluates the prevalence of LCIS in patients undergoing breast-conserving surgery (BCS) and its association with ipsilateral breast tumor recurrence (IBTR) and contralateral breast cancer (CBC) risk.METHODS: This retrospective study included women treated for stage I-III breast cancer between 2010 and 2024. Patients were divided into two groups: group 1 had invasive breast cancer only, and group 2 had concurrent LCIS and invasive cancer. Demographics, tumor characteristics, hormone receptor status, treatments, and follow-up outcomes were analyzed statistically.RESULTS: A total of 1138 patients underwent BCS, with 1103 in group 1 and 35 in group 2. The mean follow-up was 7.6 years for group 1 and 7.2 years for group 2 patients. No significant differences were found in age, family history, tumor features, or adjuvant treatments between the groups. LCIS presence did not significantly affect IBTR rates (LCIS+ 5.71% vs. LCIS- 2.17%, P=0.8401). However, CBC incidence was significantly higher in LCIS-positive patients (14.29% vs. 1.36%, P=0.0214).CONCLUSIONS: LCIS does not significantly impact IBTR rates and should not influence BCS decisions. However, due to increased CBC risk, close clinical and radiological surveillance is necessary for patients with LCIS.