Abstract PS18-08: MDA iLobulaRx: An Advanced Clinico-Patho-Therapeutic Tool for Risk Stratification in Early-Stage Invasive Lobular Carcinoma

Abstract Background: Invasive lobular carcinoma (ILC) is a distinct subtype of breast cancer that differs from the more common invasive ductal breast cancer (IDC) in its unique characteristics and arguably inferior prognosis. Recent studies have shown that ILC is associated with worse long-term outcomes compared to IDC. Risk stratification is essential in early breast cancer for tailoring treatment to optimize outcomes. We developed the MDA iLobular prognostic tool to incorporate clinical and pathological features to predict recurrence and survival in early-stage ILC (eILC). Recent studies suggest that the choice of adjuvant endocrine therapy (ET) significantly impacts recurrence and survival in eILC. We present an improved tool, “MDA iLobulaRx,” which includes clinical, pathological, and planned ET to enhance prognostic accuracy. Methods: A retrospective analysis was performed on patients treated at MD Anderson Cancer Center with a diagnosis of stage I-III ILC in our prospectively collected and curated electronic database. Primary endpoints were overall survival (OS) and distant recurrence-free survival (DRFS). Univariate and multivariate Cox Proportional Hazard (PH) regression models assessed the significance of variables. Univariate Cox analysis identified prognostic factors for further multivariate analysis. Backward and stepwise multivariate Cox PH regression identified significant factors for final models. Hazard ratios and 95% confidence intervals were estimated, considering P < 0.05 significant. We evaluated model performance using Harrell's C-index, dividing data into two-thirds training and one-third test datasets. Results: The study included 4,216 female patients with a median age of 56 years. The median pathological tumor size was 20 mm, and the median number of lymph nodes involved was one. Among these patients, 70% were post-menopausal. The ET used were tamoxifen (32%), non-steroidal aromatase inhibitor (NSAI) (30%), and no therapy (38%). The training cohort had 2,950 patients, and the test cohort had 1,266 patients. The best prognostic model for OS and DRFS had a Harrell's C-index of 0.727 and 0.713, respectively. The model included age, lymph nodes, tumor size, ER status, tumor grade, ILC histology, LCIS presence, and choice of adjuvant endocrine therapy data. (Table 1). Conclusion: MDA iLobulaRx represents a significant advancement, offering the first dedicated clinico-patho-therapeutic tool for risk stratifying eILC. Citation Format: Jason A Mouabbi, Akshara S. Raghavendra, Sarah Pasyar, Roland L. Bassett Jr., Azadeh Nasrazadani, Carlos H. Barcenas, Amy A. Hassan, Debu Tripathy, Rachel M. Layman. MDA iLobulaRx: An Advanced Clinico-Patho-Therapeutic Tool for Risk Stratification in Early-Stage Invasive Lobular Carcinoma [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr PS18-08.