Treatment for retropharyngeal metastatic undifferentiated squamous cell carcinoma from an unknown primary site: results of a prospective study with irradiation to nasopharyngeal mucosa plus bilateral neck

BACKGROUND AND OBJECTIVE: To evaluate treatment outcomes for patients with retropharyngeal metastatic undifferentiated squamous cell carcinoma (SCC) from an unknown primary site. METHODS: From January 2005 to January 2015, patients who presented with enlarged retropharyngeal nodes underwent transoral sonography-guided fine-needle aspiration to confirm histology. Those with metastatic undifferentiated SCC with unknown primary tumors were treated with radical radiotherapy to nasopharyngeal mucosa plus bilateral neck. Chemotherapy was administered for patients staged N2-3. Endpoints included metastatic nodes control, the appearance of primary tumor, overall survival and treatment-related toxicities. RESULTS: A total of 49 patients were recruited into this study. Retropharyngeal and cervical nodal disease was controlled in 96% of all patients. The incidence of occult primary cancer appearance was 8%. No primary cancer other than of the nasopharynx was detected during the course of follow-up. Ten patients developed distant metastases. The 5-year overall survival, progression-free survival, regional relapse free survival, distant metastasis free survival were 79.6%, 61.1%, 83.4%, 73.8%, respectively. Common late adverse effects included xerostomia (57%) and hearing impairment (35%). CONCLUSION: Radical radiotherapy to both the nasopharynx and bilateral neck can achieve excellent outcome with mild toxicities for patients with retropharyngeal metastatic undifferentiated squamous cell carcinoma from an unknown primary site.