Background Patients with distant metastatic Medullary Thyroid Carcinoma (MTC) have an estimated 40% ten-year survival rate. Gain of function mutations in the REarranged during Transfection or RET gene in MTC can result in an aggressive phenotype resistant to traditional therapy. In this case report, we describe the treatment of an MTC patient with a unique RET kinase deletion mutation. Case presentation Since diagnosis, 21 years ago, this patient has had chronically elevated calcitonin levels (>40,000 pg/mL) that was unable to be controlled by conventual therapy and clinical trials. As result of uncontrolled MTC, metastatic disease was found in the spine, liver, and lungs. Circulating tumor DNA (ctDNA) analysis identified a RET 898-901Del mutation, reported as a variant of unknown significance. The treating physician identified that the deletion was in the activation loop of RET kinase and considered that the mutation was constitutively activating RET kinase. The patient was prescribed Pralsetinib, a small molecule inhibitor targeting the ATP binding site of RET. Pralsetinib treatment achieved a durable response and was able to significantly decrease serum calcitonin levels (<200 pg/mL) and tumor size. Conclusion This RET deletion mutation is a pathogenic mutation with comparable enzymatic activity to the more common RET M918T mutation. The case report highlights the versatility of structural biologic approaches to guide therapeutic decisions. Show less

The prevalence of thyroid cancer is rapidly increasing worldwide, majorly due to overdiagnosis and overtreatment methods of differentiated thyroid cancer. The emergent and potent preclinical models, high-throughput molecular techniques, and genetic expression microarrays have delivered deeper insights into understanding the molecular features in oncogenesis. Thus, molecular markers have become a promising tool in managing thyroid cancer for differentiating benign and malignant tumors, prognosis, recurrence, and determination of novel therapeutic targets. In differentiated thyroid cancer, molecular markers are majorly utilized for guiding the development of indeterminate thyroid nodules on fine needle aspiration (FNA) histologies. Dissimilar to this, in advanced thyroid cancer, molecular markers permit targeted treatment of a modified signaling cascade. Determining causal mutation of targeted kinase receptors in advanced thyroid cancer can depict a promising treatment strategy with mutation-targeted tyrosine kinase inhibitors to reduce progression and eradicate mutation effects when conventional methods fail to manage. This review will focus on the molecular landscape and discuss the impact of molecular markers on the prognosis, treatment, and surveillance of differentiated and anaplastic thyroid cancer. Show less