Management and mechanism of calciphylaxis in a patient treated with the FGFR inhibitor pemigatinib-a case report.

Background: Small molecule fibroblast growth factor receptor (FGFR) inhibitors, such as pemigatinib, have been developed for the treatment of cholangiocarcinoma (CCA) with rearrangements or fusions in the FGFR2. FGFR inhibitors (FGFRis) have dermatologic side effects such as dry skin or nail bed damage. However, in very rare instances, a life-threatening vascular calcification disease known as calciphylaxis has been linked to these therapies. Case Description: We report a patient with metastatic CCA, who developed calciphylaxis following the start of their pemigatinib treatment. Calciphylaxis is associated with skin lesions and affects the dermal microvasculature in addition to the vascular calcification. This case focuses on the management strategy used for this rare adverse event (AE) as well as the pathology and complicated mechanism of calciphylaxis. We highlight the unclear pathophysiology behind this disease by identifying key players in the signaling and molecular pathways in the microenvironment that are needed to trigger this pathology. Conclusions: Calciphylaxis is normally associated with advanced renal failure in the setting of high phosphate and calcium. However, the patient we present here did not have advanced renal failure or high calcium levels and calcium dysregulation. As FGFRi use becomes more widespread, the more important it becomes to identify and have a treatment strategy for this rare AE.