Medullary Thyroid Cancer Secreting Carbohydrate Antigen 19-9 (Ca 19-9): A Fatal Case Report

Background: During follow-up for patients with medullary thyroid cancer (MTC), the levels of serum calcitonin and carcinoembryonic antigen are important, and the doubling time of these biomarkers significantly correlates with disease progression. Other antigens are present in tumor tissue and the sera of patients with MTC, but there are scarce published data on the serum levels of carbohydrate antigen 19-9 (Ca 19-9), a tumor marker primarily used for the diagnosis and follow-up of pancreatic and gastrointestinal neoplasias. Recently, the case of a 56-year-old woman with multiple endocrine neoplasia type 2B with high serum levels of Ca 19-9 was reported; this patient experienced rapid disease progression that led to her death. Case Presentation: A 28-year-old man was referred to the Department of Endocrinology of the University Hospital of Pisa with suspected MTC with laterocervical lymph node metastasis, a single liver lesion (10 mm), several bone metastases, and bilateral pheochromocytomas. RET genetic testing revealed a germline Cys634Arg mutation. During the hospitalization, the carcinoembryonic antigen and Ca 19-9 levels increased while the calcitonin concentration remained stable; despite the apparent stability of the lesions, the condition of the patient worsened rapidly and resulted in death. Conclusions: High levels of serum Ca 19-9 could be considered a marker of the dedifferentiation of MTC and disease aggressiveness, but additional data on the association between Ca 19-9 and advanced MTC are required to confirm this hypothesis.