Abstract 1314: Enhanced metastasis modeling in mice: impact of primary tumor removal and optimized injection techniques on therapeutic assessment

Abstract The clinical potential of therapies on tumor metastases can be specifically tested on metastases that have naturally developed through the migration of the tumor cells from the primary tumor. Removing the primary tumor allows for a clearer assessment of a substance’s efficacy in targeting metastatic sites alone, free from the influence of the primary tumor. If the primary tumor is still present during treatment, it is difficult to determine whether the reduction in metastatic spread is due to the anti-metastatic effect of the treatment or merely to the reduced growth of the primary tumor, which could indirectly limit the progression of metastases. In addition, the rapid growth of the primary tumor reduces the therapeutic window. The intra-mammary implantation approach (also referred to by us as subQperior for non-breast tumor cells) allows for clean surgical removal of the primary tumor, as the tumor remains isolated without adhering to the skin or peritoneum. This uncomplicated removal minimizes local trauma and residual primary tumor and provides a consistent basis for studying metastatic development after tumor resection. The study of metastasis in mouse models following primary tumor removal provides essential insights into the progression and treatment of metastatic disease. In this context, the luciferase-labelled 4T1 tumor cell line, known for its high metastatic potential, offers a robust model, particularly for investigating lung metastasis. After subQperior implantation of mice, we show that 4T1 cells even at small tumor sizes metastasize rapidly, predominantly to the lungs, making this model highly suitable for evaluating therapeutic strategies against metastatic spread. Furthermore, experiments with LL-2 tumor cells have shown that subQperior injection and removal of the primary tumor provides significantly better metastasis compared to traditional subcutaneous application. The approach of subQperior application not only increases the homogeneity and growth of the tumor and simplifies the removal of the primary tumor, but also comes closer to an orthotopic implantation with regard to the natural tumor environment and the progression of tumor growth. The advantages of subQperior injection suggest it may be a preferable method for achieving more consistent and representative metastasis in preclinical studies. Together, the methodological improvement of primary tumor removal and refined injection techniques enable a more precise evaluation of drugs targeting metastasis, avoiding confounding effects associated with the presence of the primary tumor. By isolating the impact of therapies on metastatic sites, researchers can more accurately assess the effectiveness of anti-metastatic agents, advancing our understanding and treatment of metastatic disease. Citation Format: Jonas Hummel, Philipp Metzger, Roland Sonntag, Dennis Borrero-Wolff, Gojko Bijelic, Cynthia Obodozie, Holger Weber. Enhanced metastasis modeling in mice: impact of primary tumor removal and optimized injection techniques on therapeutic assessment. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1314.