Oncological Outcomes of Breast-Conserving Surgery Versus Mastectomy in Invasive Lobular Breast Cancer: A Single-Center Retrospective Study

Background and Objectives: Invasive lobular carcinoma (ILC) is a breast cancer subtype with a controversial surgical management due to its diffuse infiltrative growth pattern and increased tendency for multicentricity. This study aimed to compare the effects of breast-conserving surgery (BCS) and mastectomy on long-term overall survival (OS) and progression-free survival (PFS) in patients diagnosed with ILC. Materials and Methods: In this single-center, retrospective, observational study, 255 patients with histopathologically confirmed ILC between 2017 and 2025 were included. Patients who underwent surgical treatment were divided into two groups according to the surgical approach: BCS (n = 94) and mastectomy (n = 141). Survival analyses were performed using the Kaplan–Meier method, and comparisons between groups were assessed with the log-rank test. Factors affecting survival were evaluated using Cox regression analysis. Results: The median age of the patients was 53 years (range, 28–85), and the median follow-up duration was 31.8 months. Of the cases, 76.9% were classic-type ILC and 70.9% had stage I–II disease. The rate of negative surgical margins was 87.6%. No statistically significant differences were observed between the BCS and mastectomy groups in terms of estimated median PFS (87.4 months vs. 86.7 months; p > 0.05) or estimated median OS (87.7 months vs. 115.7 months; p > 0.05). Multivariable analyses demonstrated that the type of surgery was not an independent prognostic factor for survival. Conclusions: This study shows that, with appropriate patient selection and adequate surgical margin control, BCS provides oncologic survival outcomes comparable to mastectomy in ILC. The choice of surgical approach should be individualized based on tumor biology, stage, and multidisciplinary evaluation rather than histological subtype alone.