SUN-331 Breaking New Ground: First Use of Peptide Receptor Radionuclide Therapy (Prrt) for Metastatic Medullary Thyroid Carcinoma in the Philippines - A Case Report

Abstract Disclosure: E.M. Gonzales: None. L.T. Tin Hay: None. M.L. Tumambing: None. E.B. Cruz: None. Introduction: Medullary thyroid carcinoma (MTC) is a rare type of thyroid malignancy which accounts for 4% of thyroid cancer, originating from parafollicular C-cells. Calcitonin is the most sensitive and specific marker for MTC and elevated levels strongly suggest the presence of residual or metastatic disease. While early stage MTC can often be managed with surgical intervention, metastatic disease poses significant therapeutic challenges with limited therapeutic options. In recent years, targeted radionuclide has emerged as a treatment modality for metastatic and progressive tumors including MTC. Among these, peptide receptor radionuclide therapy (PRRT) has shown encouraging results in terms of control and symptom management. This study, first reported use in the Philippines, highlights the role of PRRT in managing patients with metastatic MTC. Background: Patient is a known case of MTC since 2018, initially presented with enlarging neck mass on the right anterior neck with no associated hoarseness, dyspnea or dysphagia. Patient underwent total thyroidectomy with right radical neck dissection, and was maintained with Levothyroxine. Patient was lost to follow up and returned for consultation after 5 years. Work up for multiple endocrine neoplasia was done revealing negative results. 68Ga- DOTATATE PET/CT was done revealing mild to increased DOTATATE uptake in both thyroid beds, right paravertebral space, prominent to enlarged neck, mediastinal, and hilar lymph nodes, osseous lesions in the sternum, vertebrae, right humerus, right ilium, and left femur. There is likewise somatostatin receptor overexpression in a right adrenal gland mass and left pararenal lymph node. Calcitonin levels were significantly elevated from 1,176 to 46,084 pg/mL, as well as the CEA level at 289 ng/mL. Patient was advised to undergo PRRT for 2 cycles at a six-week interval. The patient received 6.02 GBq and 7.6 GBq of Lutetium-177 DOTATATE during the first two cycles, respectively. The patient tolerated the treatment with no adverse events. The post-lutetium therapy scan and repeat 68Ga-68 DOTATATE PET/CT scan after the 2nd cycle showed stable disease. Repeat calcitonin levels decreased to 36,446 pg/mL. Given the reduction in calcitonin levels and the absence of disease progression, the patient was advised to undergo an additional cycle of Lutetium-177 DOTATATE therapy. Conclusion: This case highlights the importance of multidisciplinary approach and advanced therapeutic intervention on the management of metastatic MTC. The patient demonstrated a favorable response as evidenced by decreased calcitonin levels and stable disease, indicating that PRRT can provide effective disease control in metastatic MTC. This case also underscores the potential role of the emerging therapies in improving outcomes for patients with advanced MTC. Presentation: Sunday, July 13, 2025