Abstract
Carcinoma showing thymus-like differentiation (CASTLE) is a very rare tumor occurring in the head and neck area. The histological view of CASTLE looks like squamous cell carcinoma and lymphoepithelial carcinoma, so it is difficult to diagnose correctly.
The patient was a 23-year-old woman with a swollen mass in the left neck. MRI and PET-CT findings suggested that the tumor existed only in the left lateral cervical area, and no other disease was detected in the whole body. Histological observation by open biopsy suggested metastasis of poorly differentiated carcinoma, so we considered that it was neck lymph node metastasis of carcinoma of unknown primary sites, and an operation was performed. Finally, the resected tumor was diagnosed as CASTLE after immunohistochemical staining positive for CD5 and CD117.
In this very rare case, CASTLE occurred in lateral cervical soft tissue, not the intrathyroidal area. Immunohistochemical staining for CD5 and CD117 is very helpful for diagnosing tumors as CASTLE.
