Introduction and importance Synovial cell sarcoma (SS) is an extremely rare mesenchymal malignancy, representing nearly 10% of all soft-tissue sarcomas. These high-grade soft tissue sarcomas commonly arise in the para-articular regions of lower extremities. However, 15% of Synovial sarcomas has been described at Unusual locations, including head, neck, and trunk. Herein, we describe the twelfth case of primary synovial cell sarcoma of thyroid with a literature review. Case presentation A 43-year-old woman presented with complaint of a progressive neck mass for the last five-months. She developed with dysphagia and dyspnea nearly 2 months prior, without signs of hoarseness, and weight loss. Ultrasonography in which revealed a heterogeneous, hypervascularized thyroid mass. After total thyroidectomy immunohistochemistry was in favor of primary synovial cell sarcoma of thyroid. The diagnosis was confirmed via Molecular genetic analysis of the SYT-SSX fusion gene transcript using the RT- polymerase chain reaction method. Clinical Discussion: Primary thyroid SVS is an extremely rare malignancy with poor biological behavior. SVS has been known for its tendency to local and distal re-occurrence after a few years of treatment. SS can be classified into two subtypes of monophasic or biphasic based on the presence of mesenchymal and/or epithelial components. Accordingly, the most accurate diagnostic tool for SS is considered to be molecular genetic analysis for SYT/SSX fusion transcript. Conclusion Herein, we reported an extremely rare case of SVS of thyroid gland. These high-grade soft tissue sarcomas mainly present with an asymptomatic rapid growing neck mass. Unspecific clinical presentations and extreme rarity of this disorder, make the diagnosis of thyroid SVS very challenging. Due to paucity of data, there is not enough evidence to establish a reliable mortality rate. However, the prognosis of thyroid SVS seems unfavorable.

Thyroid follicular dendritic cell sarcoma (FDCS) is an extremely rare malignancy that originates from follicular dendritic cells of the thyroid germinal centers. To the best of our knowledge, there are only 4 reported cases of thyroid FDCS in the English literature. Herein, we present the fifth case of FDCS of the thyroid gland. A 63-year-old woman presented with a painless midline neck mass, enlarging for the last 4 months. Physical examination revealed a 6-cm nonmobile, firm, multinodular thyroid mass with palpable cervical lymphadenopathy. Due to high suspicion for thyroid malignancy, the patient underwent total thyroidectomy with bilateral modified radical neck dissection. Histologic evaluations revealed sheets of storiform eosinophilic tumoral cells with prominent nucleoli containing multinucleated giant cells, and subsequent immunohistochemistry showed immunoreactivity for CD4, CD21, CD35, CD45 (LCA), and CD68. The patient was started on 6 cycles of doxorubicin, ifosfamide, and radiotherapy. She has had monthly thyroid ultrasonography and contrast-enhanced thoracoabdominal CT scan every 3 months for detecting potential recurrence and/or metastasis screening. Fortunately, 8 months after the operation, the patient is alive without any signs of local or distant metastasis.

Gastric carcinoma in young and old age adults showed no significant difference in respect of the expression of cell adhesion molecule markers. Our result shows that young age alone cannot be predictive of more metastasis and invasion potential.