Background <p>Glomangiopericytoma (GPC) is a rare sinonasal mesenchymal neoplasm with distinctive morphologic and molecular features, most commonly arising in the nasal cavity and paranasal sinuses. Occurrence in the nasopharynx is exceptionally uncommon and may create a substantial diagnostic challenge, particularly in long-term survivors of nasopharyngeal carcinoma (NPC) after radiotherapy, in whom a newly detected nasopharyngeal mass is often clinically presumed to represent recurrent carcinoma.In this setting, diagnosis should rest on the combined assessment of growth architecture, cytologic blandness, and a targeted exclusionary immunohistochemical panel rather than on clinical history, imaging appearance, or any single marker alone.</p> Case presentation <p>A man in his early seventies, previously treated with chemoradiotherapy for NPC approximately 30 years earlier, presented with a 15-day history of right-sided ptosis and headache. Nasoendoscopy demonstrated a smooth, highly vascular mass arising from the right posterior nasopharyngeal wall. Magnetic resonance imaging revealed a skull-base lesion extending toward the cavernous sinus, with radiologically suspicious cervical lymphadenopathy that was not pathologically sampled, raising concern for recurrent malignancy. Endoscopic biopsy showed a spindle-cell neoplasm composed of bland oval-to-spindle cells arranged in storiform and whorled patterns around branching thin-walled vessels. Immunohistochemically, the tumor cells showed diffuse vimentin expression, focal-to-patchy nuclear β-catenin positivity, scattered Cyclin D1 nuclear positivity, and partial Bcl-2 positivity, whereas STAT6, CD34, cytokeratin, S100, and SMA were negative. These combined morphologic and immunophenotypic findings, although not molecularly confirmed, supported the diagnosis of GPC and argued against recurrent NPC, solitary fibrous tumor, and other spindle-cell neoplasms. Because of extensive skull-base and cavernous-sinus involvement, the lesion was considered unresectable. Empirical palliative docetaxel-cisplatin treatment produced transient symptomatic improvement but was followed by fatal neutropenic sepsis.</p> Conclusions <p>This case highlights that a vascular submucosal nasopharyngeal mass arising decades after radiotherapy is not necessarily recurrent NPC. In this setting, careful histomorphologic evaluation combined with a practical immunohistochemical panel, particularly focal-to-patchy nuclear β-catenin positivity with STAT6, CD34, and cytokeratin negativity, can support a diagnosis of GPC and help avoid misclassification as recurrent carcinoma or other spindle-cell neoplasms in a previously irradiated field. Because CTNNB1 testing was not performed, the diagnosis should be interpreted as morphologically and immunohistochemically supported rather than molecularly confirmed.</p>