Calciphylaxis Cutis Associated With Fibroblast Growth Factor Receptor (FGFR) Inhibitor Therapy: A New Challenge

Specific fibroblast growth factor receptor (FGFR) inhibitors have been developed to treat malignancies harboring fusions or rearrangements in FGFR2 or FGFR3. Here, we report a case of calciphylaxis cutis in association with FGFR inhibitor therapy in a patient with FGFR2 rearranged cholangiocarcinoma. Although calciphylaxis cutis typically arises in the setting of hyperphosphatemia and end-stage renal disease, this patient had preserved renal function, normal serum calcium, and only modestly elevated serum phosphorus levels, which is similar to other recent reports of calciphylaxis in patients receiving FGFR inhibitor therapy. Calciphylaxis cutis is a possible adverse event observed with FGFR inhibitor therapy, and the mechanism of calciphylaxis cutis in association with FGFR inhibitor therapy warrants further investigation.