Abstract 672: Mapping tumor heterogeneity: Ex-Vivo drug responses in synchronous matched primary and metastatic tumors using a 3D functional precision platform.

Abstract Background: Tumor heterogeneity remains a major driver of therapeutic resistance and determining how metastatic dissemination affects functional drug response is critical for clinical decision making. We have developed a 3D microtumor functional profiling assay that preserves native tumor architecture and produces reliable drug response profiles within 7 to 10 days in a CLIA lab environment. This update expands our earlier dataset with additional synchronous pairs of cancer specimen. Methods: Matched synchronous tumors were obtained from primary ovary, colon, and breast cancers with metastases into the omentum, liver, peritoneum, lung, and axilla. All samples were cooled and shipped overnight, processed within 24 hours, and exposed to NCCN recommended and mechanistically relevant chemo or targeted therapies. Viability was assessed after 72 h to generate cytotoxicity dose responses and concordance was measured using coefficient of determination (R2). Results: We are reporting on 162 drug comparisons from seven patients with matched primary and metastatic tumors. Drug-response concordance varied substantially by metastatic route. Local metastases showed the highest correlation. A lymphogenic metastasis (breast to axilla) showed moderate correlation. Hematogenic metastases exhibited the weakest correlation, with colon-lung and ovarian soft-tissue/colon pairs showing only modest similarity. However, one ovarian local spread to the omentum demonstrated only moderately strong correlation. Conclusions: The data suggest that sensitivity and resistance spectra from local metastases tend to correlate well with those from the primary tumors. Furthermore, for metastases from lymphogenic or hematogenic spread, while the correlation tends to be only modest, functional profiling may still be useful to significantly reduce the risk for receiving ineffective treatment. Citation Format: Rajeshwar Nitiyanandan, Ivan Trus, Chiara Maestri, Ricardo J. Parker, Chris Apfel. Mapping tumor heterogeneity: Ex-Vivo drug responses in synchronous matched primary and metastatic tumors using a 3D functional precision platform abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 672.