Rare Thyroid Cancers and Metastasis into the Thyroid
There are rare types of cancer that could spread to or araise within the thyroid gland. Thyroid involvement by metastatic disease is an uncommon but well-documented occurrence. Metastatic disease to the thyroid is an uncommon but welldocumented event and accounts for 1–9 % of all thyroid malignancies. Therefore, metastatic disease should be considered in the differential diagnosis in patients with a prior history of cancer with new thyroid nodules or thyromegaly.
Thyroid paraganglioma is an extremely rare tumor and frequently mistaken for other thyroid neoplasms. Paraganglioma is a neuroendocrine tumour derived from extra-adrenal cells of the neural crest paraganglia of the autonomic nervous system. These rare neoplasms comprise of around 0.012% of head and neck tumours. Radiological examinations is nonspecific and none had been diagnosed correctly before surgery. Accurate diagnosis relies on the histopathogical findings and adjunctive immunohistochemcial studies after removal of the tumor. To date, all the reported cases have pursued a benign course. Although atypical features seem to have no association with clinical behavior, long time postoperative surveillance with biochemical screening of hormone secretion, cervical ultrasonography and whole-body CT scan is recommended.
Squamous Cell Epidermoid Carcinoma of the Thyroid
Primary squamous cell carcinoma (SCC) of the thyroid gland is an extremely rare malignancy that presents with advanced disease and poor prognosis. This type of thyroid malignancy is seen less than 1% of all thyroid cancers and is highly lethal. Metastatic disease should always be excluded. It is difficult to diagnose the carcinoma in the early stage. FNA Biopsy should be strongly recommended. The best treatment for SCC of the thyroid is early diagnosis and aggressive surgery combined with radiation and chemotherapy. Unfortunately, due to its aggressive behavior, complete surgical resection is rarely possible. A median survival time of 6.5 months was reported.
Fibrosarcoma of the Thyroid
A primary sarcoma may develop in any organ due to the ubiquity of mesenchyma in the human body. Fibrosarcomas affect organs containing fibrous tissue, most often the lower and upper limbs as well as the trunk. The thyroid is extremely rarely affected by fibrosarcoma. Thyroid sarcomas constitute less than 1% of all thyroid tumors. Primary fibrosarcoma of the thyroid gland has very rarely been presented in literature. The prognosis is poor and the recommended treatment is surgical resection.
Metastases to the Thyroid Gland from Renal Cell Carcinomar and Other Cancers
The three most common neoplasms to metastasize to the thyroid were from the kidney (Renal Cell Carcinoma [RCC]), lung, gastrointestinal tract and breast, respectively. Also melanoma and colorectal cancer could have metastatis into the thyroid gland. Malignant mesothelioma is an aggressive tumor with a poor prognosis as the median survival is 12 months from diagnosis. Malignant mesothelioma most commonly spreads to the pleural cavity and neighboring organs such as the lung and chest wall, but rarely presents with distant metastases. Intrathyroidal metastases secondary to malignant mesothelioma has only been reported in three prior cases, both of which were diagnosed by FNA. Metastases to the thyroid gland from renal cancer pose a challenge to physicians, due in part to the rarity of the phenomenon, the prolonged time interval between removal of the primary renal cancer and the appearance of metastases, the difficulty in diagnosis, and the uncertainty regarding long-term prognosis. Surgical treatment of solitary thyroid metastases is recommended. The treatment options in patients with metastatic disease to the thyroid gland should be made based upon the condition of the patient, extent of the disease, stage, and volume. However, most patients with thyroid metastases have widespread disseminated disease, which is associated with a poor prognosis, and palliative care is the indicated recommendation.
The overall prognosis of the patient may also vary with the histologic grade and subtype of the primary neoplasm. Patients with metastatic renal and breast carcinoma were reported to have an average of 32 and 37 months after thyroidectomy versus patients with lung and gastrointestinal carcinoma with an average of 1.5 and 2 months after thyroidectomy. Therefore, patients with certain malignancies such as renal carcinoma are associated with improved overall survival while others such as lung carcinoma are associated with a poorer prognosis. Radiation and chemotherapy is often reserved as palliative care for patients with widespread disease or in those with comorbidities which precludes surgical intervention.
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