Prognostic Value of ¹⁸F-FDG PET/CT in Patients with Metastatic Squamous Cell Carcinoma of Unknown Primary Presenting as Cervical Lymphadenopathy

Objectives In metastatic squamous cell carcinoma of unknown primary presenting as cervical lymphadenopathy (MSCCUP-CL), it was not reported whether ¹⁸F-FDG PET/CT quantitative parameters were associated with prognosis. We investigated the prognostic values of PET parameters in patients with MSCCUP-CL.

Methods Subjects were 36 patients (M:F = 28:8; 65.8±8.9 y) with histologically proven MSCCUP-CL, where primary site was not found after standard work-up including CT, PET/CT and panendoscopy. The maximum standardized uptake value (SUVmax), average SUV, metabolic tumor volume (MTV), and total lesion glycolysis (TLG) of metastatic cervical lymph nodes were measured. Overall survival (OS) and progression-free survival (PFS) were assessed. Analysis using a Cox proportional hazards regression model were determined to evaluate the prognostic significance of these PET parameters.

Results Disease progression or cancer-related death occurred in 19 (53%) or 8 (22%) of 36 patients, respectively. On univariable analysis, the extent of metastatic lymph nodes (cervical vs. extracervical), MTV (cut-off=36.3) and TLG (cut-off=206.9) of metastatic cervical lymph nodes, and treatment modality (surgery-based therapy vs. non-surgical therapy) were significant predictors for both OS and PFS. On multivariable analysis, male (HR=10.33, p=0.013), non-surgical palliative treatment (HR=29.94, p<0.001), and larger MTV or TLG (HR=3.078 p=0.041) indicated poor prognosis for progression. Treatment modality (HR=13.56, p=0.023), and MTV or TLG (HR=5.75, p=0.045) were identified significant prognostic factors associated with decreased overall survival.

Conclusions The volumetric PET parameters such as MTV or TLG of metastatic cervical lymph nodes are independent significant prognostic factors for OS and PFS in addition to treatment modality in patients with MSCCUP-CL. ¹⁸F-FDG PET/CT may be a promising tool for risk stratification and better prediction of outcome in those patients.