Diagnostic and prognostic values of 18F-FDG PET/CT in cervical nodal metastatic carcinoma of unknown primary site

Objectives Carcinoma of unknown primary (CUP) represents a heterogeneous group of metastatic malignancies for which primary tumor site could not be identified after routine diagnostic methods. Cervical lymph nodes are relatively superficial and easily to be found, therefore, a majority of CUP patients are cervical nodal metastases of CUP (CCUP). The aim of this study was to investigate the diagnostic and prognostic values of 18F-FDG PET/CT in patients referred with CCUP.

Methods A total of 137 consecutive patients (95 males, 42 females, age range 24-84 y [average 55.77±11.71 y] ) with histological proven CCUP who underwent 18F-FDG PET/CT imaging to find primary tumors from Jan 2010 to Jun 2015 were retrospectively analyzed. The golden standard was the final clinical pathological diagnosis or long-term follow-up (蠅6 months) results, and the average time of follow-up was 21.7 months. The diagnostic sensitivity, specificity, accuracy, PPV and NPV of PET/CT imaging in detecting primary tumors were calculated. Kaplan-Meier analysis was conducted for survival analysis and to identify the presence of any prognostic factors (including age, gender, presence or absence of distant metastasis, side of lymph node involvement, histopathologic tumor type and primary site found or not by PET/CT imaging).

Results Of 137 patients, a total of 96 patients found primary tumors, in which 52 patients were diagnosed with pathology, and 44 with long-term follow-up. Whole-body 18F-FDG PET/CT scan correctly detected the primary tumor in 87 CCUP patients. The diagnostic sensitivity, specificity, accuracy, PPV and NPV were 90.6% (87/96), 80.5% (33/41), 87.6% (120/137), 91.6% (87/95) and 78.6% (33/42) respectively. Head/neck and lung were the most commonly primary tumor sites. However, the false positive and negative cases were also mainly seen in these sites. Fifty-six patients died in this set of cases, and the median survival time was 14 months. Discoveries of distant metastasis and inferior region of cervical lymph nodes metastasis (according to AJCC cervical lymph nodes classification, IV, V B, VI and VII as the inferior region) were associated with worse survival (χ2=20.990 and 12.277, respectively, both P6.5 were of higher mortality risk than those with SUVmax&#8804;6.5 (χ2=7.120, P<0.01).

Conclusions Whole-body 18F-FDG PET/CT scan is a valuable tool in the identification of the primary tumor site in patients with CCUP. Without the need of identification of the primary tumors, 18F-FDG PET/CT scans are of value in the assessment of prognosis according to the distant metastasis and region of cervical lymph nodes metastasis. This work was supported by the National High-tech R & D Program of China (863 Program, No. 2008AA02Z426).