Poorly differentiated thyroid carcinomas represent a rare heterogeneous group of malignant tumors that constitute approximately 2-4% of all thyroid neoplasms. Substernal Goiter is defined as an enlargement of the thyroid gland that is located below the thoracic inlet. Malignant neoplasms arising from a substernal goiter were reported in only 2-3% of cases. This case report has been reported in line with the SCARE Criteria.