Background. The unknown primary carcinoma in the head and neck has been estimated to represent up to 7% of all head and neck carcinomas. In an attempt to identify the occult primary tumor the evaluation of this patient population has included a complete head and neck examination, flexible fiberoptic endoscopy, and imaging with CT/MRI. More recently, positron emission tomography (PET) has been advocated as a tool to detect primary tumors. Methods. A cohort of 31 patients with fine-needle aspiration biopsy-confirmed squamous cell carcinoma were prospectively entered into a diagnostic protocol to identify the occult primary tumor. The diagnostic protocol included a comprehensive head and neck examination (including flexible endoscopy) and CT and/or MRI. If the initial diagnostic evaluation failed to identify a primary tumor, the patients then underwent whole body PET imaging followed by staging endoscopy with biopsy of the at-risk occult tumor sites. The outcome measures included the accuracy of the PET to predict the presence of occult tumor at staging endoscopy and the accuracy of the negative PET and negative panendoscopy in predicting the subsequent development of a primary tumor in the upper aerodigestive tract during follow-up. Results. The PET detected 9 occult primary tumors in the 31 patients (detection rate, 29%). Five occult primary tumors (2 base of tongue and 3 palatine tonsil) were detected during panendoscopy despite a negative PET. The combination of PET and panendoscopy detected 45.2% of the unknown primary tumors. Seventeen patients (N1, n = 7; N2a, n = 4; N2b, n = 2; N3, n = 4) had no primary tumor detected and were treated as an unknown primary carcinoma with primary neck dissection +/-radiation therapy +/- chemotherapy. In this series of 17 patients, there were 3 neck recurrences (17.6%). In addition, only 1 patient (5.8%) developed a primary tumor of the upper aerodigestive tract with a mean follow-up of 31.1 months (range, 21-60 months). Conclusion. A negative PET study in patients with an occult primary head and neck carcinoma does not preclude the need for panendoscopy with biopsy to detect the occult primary tumor. The risk of subsequent primary tumor appears to be low in the patients with a negative PET and a negative panendoscopy (<6%).
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