Phosphaturic mesenchymal tumor (PMT) is a rare neoplasm in which the tumor cells produce fibroblast growth factor 23 (FGF23), leading to oncogenic osteomalacia and thus a distinct clinical presentation.

However, the pathologic findings of PMT are often non-specific and variable, especially in tumors occurring in the head and neck.

We present a case of a 66-year-old female who presented with osteomalacia-related symptoms and was found to have a nasal cavity mass.

Histopathologic examination was suggestive of PMT but certain characteristic features were lacking, requiring confirmation of the diagnosis by chromogenic in situ hybridization (CISH) assay for FGF23 mRNA.

The patient's symptoms and laboratory abnormalities resolved upon resection of the tumor.