Abstract #1399687: Precision Oncology in the Management of Medullary Thyroid Cancer in an Adolescent with MEN2B, 1-year Follow-up

Abstract

Medullary thyroid carcinoma (MTC) is a rare but aggressive thyroid tumor, with 25% of hereditary and 75% of sporadic forms. RET mutations are found in 98% of hereditary MTC and in 55% of sporadic MTC. Targeted therapies are a management option for patients with progressive or symptomatic disease with locoregional or metastatic MTC. We present the case of an adolescent with type 2B multiple endocrine neoplasia (MEN-2B) syndrome with an optimal response to pralsetinib. A 14-year-old adolescent, she was admitted for maxillofacial surgery in September 2019 due to a thyroid nodule and cervical nodes whose FNA reported: MTC; she underwent total thyroidectomy extended to prethyroid muscles + bilateral radical dissection. The pathology reported: multicentric MTC: in LTL tumor of 3.0 x 1.5cm, with invasion of tumor capsule and extraglandular 4mm to the adiposomuscular plane, lymphatic and venous permeation, tumor in isthmus of 1cm and RTL of 0.6cm; Bilateral periglandular and cervical lymph node metastasis (23/58) EC-IVA. Endocrinological evaluation showed a marfanoid phenotype, thick lips, tongue neuromas, diastema, and a history of chronic constipation with segmental colonic dilatation on abdominal radiography. No history of HTA. No similar family history. PET-CT-18FDG: mediastinal lymph nodes suggestive of metastasis. She received cervical-mediastinal radiotherapy: 6000 cGy in April 2020. Follow-up was interrupted due to a pandemic, she was readmitted with mediastinal disease progression according to PET-CT in June 2021. She had access to a genetic NGS tumor study that showed the RET M918T mutation. In December 2021, she started Pralsetinib 200 mg/day, achieving a biochemical and structural response in follow-up sustained to date, without developing major adverse events. The NCCN Guidelines advise performing the RET study at the time of initial diagnosis. Targeted therapies have helped supplant cytotoxic chemotherapy, which has low efficacy against disease progression, but there is still the problem of toxic side effects and frequent development of tumor resistance when using the current treatment regimen. In this case, with the MEN-2B criteria established, the RET M918T mutation detected. and presenting with disease progression (elevated calcitonin and CEA, associated with mediastinal disease progression), she agreed to an expanded program of anti-RET therapy with Pralsetinib, demonstrating safety and efficacy after 1 year of use.