Collision metastasis of squamous carcinoma of the oral tongue and incidental thyroid papillary carcinoma to a single cervical lymph node.

The incidence of collision tumor is exceedingly rare. There are only four published case reports. This is the first report of a case of collision metastasis of squamous cell carcinoma (SCC) of the oral tongue and incidental thyroid papillary carcinoma to the same cervical lymph node. A 47-year-old man with SCC of the oral tongue at clinical stage T4N1M0 was treated with total glossectomy and bilateral neck dissection. During neck dissection, concomitant secondary foci of thyroid papillary carcinoma were identified in the same cervical lymph node as SCC (collisional metastasis). The patient subsequently underwent total thyroidectomy and was alive without any recurrences at 25 months after the operation.