A neck node biopsy in a 45-year-old shows metastatic squamous cell carcinoma. PET-CT and panendoscopy fail to reveal a primary tumor. p16 immunostaining of the node is strongly positive. The most likely occult primary site is:
- A Oral cavity
- B Hypopharynx
- C Oropharynx (tonsil or base of tongue) — HPV-related ✓
- D Larynx
Correct answer: C. Oropharynx (tonsil or base of tongue) — HPV-related
Explanation
p16 overexpression serves as a surrogate marker for high-risk HPV (particularly HPV-16) infection. HPV-related squamous cell carcinomas arise predominantly in the oropharynx (tonsillar crypts and base of tongue). In carcinoma of unknown primary (CUP) with p16-positive metastatic nodes, the occult primary is almost always oropharyngeal, even when undetected by standard imaging. This subset has a better prognosis than HPV-negative head and neck SCC.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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