Patient-Derived Tumor Organoids as Predictive Models of Treatment Response in Locally Advanced Rectal Cancer

Locally advanced rectal cancer (LARC) presents significant interpatient heterogeneity in response to neoadjuvant chemoradiotherapy (nCRT), and current clinical and radiological criteria lack sufficient predictive value. Patient-derived tumor organoids (PDTOs) have recently emerged as reliable in vitro three-dimensional models that preserve both architectural and genomic fidelity to the parental tumor. We conducted a prospective, non-randomized interventional study at the Mediterranean Oncology Institute, enrolling 25 patients with histologically confirmed LARC eligible for nCRT and curative surgery. A total of 20 endoscopic rectal tumor biopsies were obtained prior to treatment. Organoid generation was attempted in 12 samples, with 3 resulting in spheroid formation and only 1 yielding a stable organoid culture. Histological comparisons were performed using H&E staining and immunohistochemistry, while molecular profiling was conducted via targeted next-generation sequencing (NGS) using a 161-gene panel. Comparative analyses demonstrated a high degree of morphological and immunophenotypic similarity between tumor tissue and organoid. Molecular profiling confirmed the conservation of key mutational events, with high concordance in single nucleotide variants (SNVs) and mutational signatures between the paired tumor and organoid. Despite a limited organoid formation rate (8.3%), likely due to sample variability and processing limitations, the derived model retained relevant oncogenic features. This study provides proof-of-concept evidence supporting the feasibility and translational relevance of PDTOs in LARC. Although technical challenges remain—particularly in standardizing culture conditions and improving yield—organoid-based models may serve as powerful predictive tools for personalizing therapeutic strategies. Ongoing work aims to optimize culture protocols, expand the cohort, and evaluate in vitro therapeutic sensitivity assays in correlation with clinical outcomes