Patient-derived medullary thyroid cancer organoids: a potential model for mechanistic studies on diagnostics and therapy

Objective: Medullary thyroid carcinoma (MTC) is a rare neuroendocrine thyroid tumor, with only 30 new patients annually in theNetherlands. PET imaging provides information on distantmetastases, afterwhich tyrosine kinase inhibitors (TKIs) may be initiated. The rarity of the disease impedes large controlled trials, and therefore the challenge of selecting the best TKI and PET tracer for individual patients persists. To explore whether an in vitro model could be developed to guide the selection of appropriate PET tracers or TKI therapies in the future, we aimed to establish an MTC organoid model for the first time. Methods: Dispersed cells from MTC biopsies were suspended in Matrigel, allowing organoid formation. The self-renewal potential was tested by dissociation and re-plating cells and determining organoid-forming efficiency. MTC-specific gene and protein expression were characterized by qPCR and immunofluorescent staining. Moreover, MTC-organoids (MTOs) were exposed to TKIs and PET tracers in proof-of-principle experiments. Results: Ten MTC biopsies were processed and successfully cultured as MTOs. MTC-derived cells showed self-renewal potency for several passages, indicating the presence of putative stemcells. Gene and protein expression ofMTC-specific markers in tissue and MTOs, and function measurements showed the production of calcitonin and CEA. Interpretation of the preliminary experimentswith TKIs and PET tracerswas limited by sample size but demonstrates their future potential. Conclusion: We were able to culture MTC organoids that resemble the original tissue in gene expression, protein expression, and functionality. However, international, multi-center studies are required to meet the standards for future clinical applications.