Clinical-pathological characteristics associated with multigene assay risk scores, and prognostic impact of multigene risk scores in patients with invasive lobular carcinoma.

546 Background: Invasive Lobular Carcinoma (ILC), a unique breast cancer subtype, exhibits distinct clinical and pathological features. Multigene assays, notably the Oncotype DX (ODX) test, provide personalized prognostic insights in breast cancer. However, a research gap exists for clinical-pathological characteristics affecting multigene assay risk scores in ILC. This study aims to address this gap, investigating factors specific to ILC, distinct from those in invasive ductal carcinoma (IDC), contributing to refined risk stratification and personalized treatment decisions for ILC patients. Methods: Retrospective analysis was conducted on 238 ILC type breast cancer patients who underwent surgery at AMC between 2012 and 2022 and had undergone the ODX test. The ODX test assessed the Recurrence Score (RS) with defined categories: low (0-15), intermediate (16-25), and high (26 or above). Additionally, binary analysis categorized patients into low and high-risk groups using a cutoff of 25. The cutoffs were determined based on existing research findings. Results: Among patients undergoing ODX testing, the distribution of RS differed significantly between ILC and invasive ductal carcinoma (IDC) patients. Notably, the percentage of high-risk cases was higher in ILC (4.2%) compared to IDC (16.9%). Examination of patient characteristics revealed a prevalence of younger individuals, premenopausal status, and those undergoing breast-conserving surgery (BCS) among the low-risk binary group. In multivariate logistic regression analysis, PR negativity emerged as a significant factor influencing ODX high risk across the entire cohort (OR 23.224, 95% CI 3.732-144.527, p=0.001). Subgroup analysis by age identified specific risk factors, including PR negativity in younger patients (OR 11.896, 95% CI 1.247-113.523, p=0.031), larger tumor size (more than 2cm) (OR 4.180, 95% CI 1.229-14.214, p=0.022), and PR negativity in older patients (OR 25.030, 95% CI 3.505-178.756, p=0.001). Conclusions: In ILC, factors predicting ODX differ from IDC, emphasizing the need for tailored risk prediction models. PR negativity emerged as a consistent predictor of ODX high risk, warranting attention in risk stratification models. Recognizing this distinction is crucial for enhancing precision in prognostic assessments and optimizing patient management in ILC.