Blood Liquid Biopsy in an Advanced Medullary Thyroid Carcinoma: A Case Study with Rearranged during Transfection Heterogeneity

Introduction: Liquid biopsy is an innovative and efficient method for studying circulating tumor DNA. In conjunction with innovative techniques such as next-generation sequencing, it can provide real-time information on prognostic and predictive factors. Case Presentation: We report a case of advanced, unresectable medullary thyroid carcinoma with various rearranged during transfection (RET) and Kirsten rat sarcoma viral (KRAS) mutations in both blood liquid and tissue biopsies. After the initial failure of treatment with a tyrosine kinase inhibitor (TKI), a liquid biopsy analyzed by next-generation sequencing showed the presence of six different RET mutations and KRAS. Tissue biopsy also revealed two RET mutations. Due to these biopsy findings, the treatment was changed to another TKI, and the patient is now clinically stable. Discussion/Conclusion: Liquid biopsy makes it possible to analyze different genetic alterations that may have implications as predictive factors. It also reveals tumor heterogeneity and its implications for prognostic factors.