Tumor Related- and Non-tumor-Related Diarrhea in a Medullary Thyroid Cancer Patient

Medullary thyroid cancer (MTC) is a rare malignancy originating from calcitonin-producing parafollicular C cells of the thyroid. In advanced disease, hormonal secretion by the tumor cells of calcitonin or other active peptides can cause systemic symptoms. Occasionally, MTCs release corticotropin (ACTH) causing ectopic Cushing’s syndrome. Although the pathogenesis is unclear, diarrhea and facial flushing are more common in MTC, and the management of potentially disabling symptoms is essential to improve the quality of life of these patients. Adequate symptomatic control is needed because chronic diarrhea impairs the quality of life and, when severe, may cause volume depletion and acid-base and electrolyte abnormalities. The initial treatment approach is based on the use of antimotility agents, while somatostatin analogs are a cornerstone in the management of carcinoid syndrome-related diarrhea. Multikinase inhibitors used for the treatment of progressive, advanced disease may also cause diarrhea as a drug-associated adverse event. This case report describes the management of a man with MTC who suffered from diarrhea as the main symptom of the disease. Diarrhea was the earliest, misdiagnosed symptom at presentation of MTC as well as an adverse event of systemic treatment (cabozantinib).