HPV ‐Positive Squamous Cell Carcinoma Metastasis Without Clinical Evidence of Primary: The Posterior Oropharyngeal Wall May Be an Overlooked Location

Background Oropharyngeal squamous cell carcinoma (SCC) can present as cancer of unknown primary, where only cervical lymph node metastases are identified. Most tumors, particularly human‐papillomavirus‐associated ones, are located in the palatine/lingual tonsils. When this is not the case, additional imaging with 2‐deoxy‐2‐[ 18 F]fluoro‐D‐glucose positron emission tomography ([ 18 F]FDG‐PET) and ultrasound can be helpful. Methods A 68‐year‐old male with bilateral cervical metastasis from an HPV‐positive SCC, no primary tumor was identified despite thorough examination. [ 18 F]FDG‐PET revealed bilateral cervical metastases and a possible primary tumor in the posterior oropharynx. Guided by perioperative transoral ultrasound, a biopsy for frozen sectioning was obtained. Results Frozen sectioning of the posterior tumor revealed SCC. Final histology confirmed the posterior wall tumor as the primary cancer. Conclusions The posterior oropharynx wall must be carefully investigated during the diagnostic workup for SCC of an unknown primary tumor as it can be the site of the primary tumor. Identification of the primary tumor reduces the need for further diagnostic surgery.