A case of intrathyroid thymic carcinoma treated with radiotherapy

Intrathyroid thymic carcinoma is a rare malignant tumor that originates from residual thymic tissue within the thyroid.We report a case of unresectable intrathyroid thymic carcinoma treated with definitive radiation therapy.The patient was an 88-year-old female.Physical examination revealed a mass caudal to the inferior pole of the right thyroid lobe, and endoscopic examination observed right vocal cord paralysis.CT and MRI indicated a tumor lesion in the right upper mediastinum infiltrated into the right lobe of the thyroid gland, common carotid artery and trachea.For diagnostic purposes, a biopsy was performed under general anesthesia resulting in a diagnosis of poorly differentiated squamous cell carcinoma.Pathologically, the boundary between the normal thyroid tissue and the tumor was unclear, leading to the conclusion that the tumor originated from thyroid gland and it was diagnosed as intrathyroid thymic carcinoma.As the tumor was unresectable, definitive radiation therapy was performed.Five years after treatment, the tumor has shrunk without regrowth.Intrathyroid thymic carcinoma is highly sensitive to radiation.Although there is no established treatment for unresectable cases, definitive radiation therapy may be considered as an option of treatment.