Objective  To investigate the characteristics, diagnosis, primary detection, and prognosis of cervical lymph node metastases of squamous cell carcinoma of unknown primary site (SCCUP).

  Methods  This study retrospectively analyzed the clinical features and follow-up data of 262 patients with SCCUP. The Chi-square test were used to analyze the clinical performances, characteristics of primary lesions, and sensitivity and specificity of examinations to identify original lesions. Factors related to the overall survival (OS) and progression-free survival (PFS) were also analyzed.

  Results  The 262 patients with SCCUP comprised more men, with a median age of 57 years. At the follow-up, 70 patients were diagnosed with primary lesions (26.7%), and the detection rates of primary lymph nodes in those who were male (30.1%), with a single lesion site (31%), and with level Ⅳ disease (39.3%) were higher than those in patients who were female (17.4%), with multiple lesion sites (18.7%), and with level Ⅱ/Ⅲ disease (20.8%). Compared with traditional imaging examinations, ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) had higher sensitivity and specificity in detecting the primary tumor. Survival analysis showed that distant metastasis was an independent risk factor affecting OS and PFS, and the effect of N stage on PFS was statistically significant.

  Conclusions  In SCCUP patients, the proportion of patients who were male, with a single lesion site, and with cervical Ⅳ lymph node metastasis had higher rates of detection of the primary sites. PET/CT examination is important for the diagnosis of SCCUP, as well as the detection of primary lesions. Advanced N stage and distant metastasis indicated poor prognosis.