Implication of 18F-fluoro-2-deoxy-D-glucose positron emission tomography on management of carcinoma of unknown primary in the head and neck: a Danish cohort study

Objectives. To demonstrate the efficacy of whole-body 18F-fluoro-2-deoxy-D-glucose positron emission tomography (18F-FDG PET) in the detection of a carcinoma of unknown primary after conventional diagnostic workup in patients with a metastatic neck lesion and to demonstrate how the treatment policy of wide-field irradiation can be safely modified in relation to the findings from PET scanning. Study Design: Prospective cohort study of consecutive patients. Methods. Forty-two consecutive patients with squamous cell or undifferentiated metastatic disease in the neck from a carcinoma of unknown primary were enrolled after standard clinical workups. These patients underwent extensive clinical investigations including endoscopy under anesthesia with multiple mucosal biopsies and diagnostic imaging as well. If no primary site was indicated at this stage, a whole-body 18F-FDG PET scan was performed. Results. Potential focal pathological uptake indicated a primary tumor in 20 of 42 cases (48%). After PET, this was confirmed by additional investigations in 10 patients (24%). Of these, seven primaries were found in the head and neck region (hypopharynx [three], base of tongue/vallecula [two], nasopharynx [1], floor of mouth [1]), and three primaries were found below the clavicles (lung [1], esophagus [1], and abdomen [1]. Positron emission tomography resulted in significant modifications of radiation treatment fields or fractionation prescriptions in all the patients who were diagnosed with a primary tumor after PET. Conclusion: With our present strategy of wide-field irradiation in patients with neck node metastases from a carcinoma of unknown primary, whole-body 18F-FDG PET had treatment-related implications in 24% (10 of 42) of the patients.