Before trying to understand metastatic thyroid carcinoma, you have to know the concept called "metastasis" first. Metastasis is the movement or spread of a disease or an infection from one organ to another non-contiguous organ. The term is often used to refer to cancer cells. Malignant tumor cells usually spread through the bloodstream or the lymph system. They penetrate into lymphatic and blood vessels, circulate throughout the body and grow in normal cells, tissues, or organs located somewhere else in the body far from the primary tumor.
New tumors formed through metastasis is called a metastatic or secondary tumor. Its cells are the same as that of the original or primary tumor. For example, if pancreatic cancer spreads to the liver, the metastatic tumor is made up of abnormal pancreatic cells and not liver cells. The disease is called “metastatic pancreatic cancer.”
So what is metastatic thyroid cancer? It is the disease formed by thyroid cancer cells growing in an organ far from the thyroid. For example, if thyroid cancer spreads to the stomach, the cancer cells in the stomach are thyroid cancer cells. That is a metastatic thyroid cancer. It will, then, be treated as thyroid cancer, not as cancer of the stomach. The original tumor must be treated just the same.
To treat a metastatic carcinoma, many factors have to be taken into consideration. What stage is the cancer in? Is the cancer papillary, follicular, medullary, or anaplastic? Where is the original tumor located? Where is the metastatic or secondary tumor located? What organ did it grow in? How old is the patient?
The treatment will be the same as to an ordinary thyroid cancer. Surgery is still the most common and the easiest way to solve the problem. Total thyroidectomy is usually performed. After the operation, the patient undergoes radioiodine scanning to find metastatic tumor cells growing somewhere distant from the thyroid. Radioablation of any residual disease follows. Chemotherapy also works and can also be used for curing metastatic thyroid cancer.