Gastropharyngeal Anastomotic Leak in Medullary Thyroid Carcinoma Following Initiation of a Tyrosine Kinase Inhibitor: A Case Report of an Unusual Side Effect of Cabozantinib

Background: Medullary thyroid carcinoma (MTC) accounts for 1% to 2% of thyroid cancers in the United States. When identified early, total thyroidectomy is most often curative. However, in advanced disease, more aggressive treatment such as laryngectomy and esophagectomy may be indicated. Postsurgical fistula formation and leak is a potential complication in such cases. These fistulas are most likely to occur at the anastomotic site in cases of laryngectomy or esophagectomy. Concomitant chemotherapy and radiation increase this risk. Tyrosine kinase inhibitors (TKI) such as Cabozantinib are used as therapy for metastatic MTC. These drugs have previously been associated with dehiscence of anastomotic sites in the gastrointestinal tract. While previously identified in the bowel, this report represents the first documented case of gastropharyngeal anastomosis leak described in the context of TKI use for head and neck cancer. Case Presentation: We present the case of a 72-year-old male previously diagnosed with MTC. His gastropharyngeal anastomosis status-post laryngopharyngectomy and gastric pull up had been stable for 23 years. Over the past year, he developed back pain and was found to have spinal metastases of MTC. He was subsequently started on Cabozantinib to slow the progression of the disease. Within months of starting this TKI, a bleeding pharyngocutaneous fistula developed at the anastomosis site of the gastric pull up and pharynx. Upon discontinuation of Cabozantinib, the fistula healed with no further complications. Conclusions: To our knowledge, this is the first documented case of gastropharyngeal anastomotic leak related to TKI use. A causal relationship is highly plausible given the previously stable anastomosis and the suspicious advent of complications within months of initiation of this new drug. While previously limited to cases of intraabdominal bowel dehiscence, this report now suggests that wound dehiscence must be considered a known side effect of TKIs throughout the gastrointestinal tract, including the gastropharynx. As such, the risk of anastomotic dehiscence should be discussed with the patient prior to starting a TKI.