Simultaneous squamous cell carcinoma and papillary adenocarcinoma of the thyroid gland

A case of simultaneous squamous cell carcinoma and papillary adenocarcinoma in the thyroid gland is reported. A pure squamous cell carcinoma arose in the right lobe, and a pure papillary adenocarcinoma without squamous metaplasia arose in the left lobe. Both cancers came into collison at the isthmus. The case is unique in that the tumor was a so-called collison tumor but not a mixed tumor.