B. Metastatic squamous cell carcinoma
Histopathology revealed p16-positive squamous cell carcinoma of bilateral thyroid lobes, and 13 of 20 positive lymph nodes, involving left neck levels 2 through 5 and 6, with extranodal extension. The diagnosis of HPV-related metastasis was confirmed with RNA in situ hybridization for high-risk HPV (types 16, 18, 31, and 33) showing hybridization in areas of p16 immunoreactivity. Biopsy results of thyroid tumor cells were negative for chromogranin, synaptophysin, and CD56, excluding an underlying neuroendocrine component. The patient was subsequently treated with reirradiation and cisplatin.
Metastasis to the thyroid represents only 1.4% to 3% of all thyroid cancers.1 In a series of 97 patients with metastatic cancer to the thyroid, a head and neck primary site was identified in 12 (12%).1 Squamous cell carcinoma of the thyroid can present as primary thyroid cancer or secondary involvement from direct extension of adjacent disease, typically from the larynx.2 To our knowledge, there are only 19 published articles comprising a total of 32 patients with squamous cell carcinoma of the head and neck metastasizing to the thyroid.2 Of these cases, only 3 involved oropharyngeal primary sites. Nasopharyngeal cancer was the most commonly reported primary site.2,3