The tumor can be of any size and the cancer may have spread from the thyroid to the nearby neck muscles. It is known that the primary mode of spread in papillary thyroid carcinoma (PCT) is through lymphatic vessels, while bloodborne metastases to distant sites are rare. The known sites of distant dissemination in PCT are bone, lung, skin, and brain, while involvement of the recurrent laryngeal nerve, larynx, pharynx, trachea, and esophagus occurs due to direct infiltration. Distant metastases have also been reported to the kidney, cerebellum, skin and esophagus.
Most patients with thyroid cancer have the cancer contained in the thyroid at the time of diagnosis. About 30% will have metastatic cancer, and most will have spread to the lymph nodes in the neck and only 1 to 4% will have spread the cancer outside the neck to other organs, such as the lungs and bones. Despite this, most patients with thyroid cancer have an excellent prognosis, even if there is spread outside the neck at diagnosis. In order to determine factors that predict prognosis for those with metastatic cancer outside the neck, a study was conducted using data from Memorial Sloan-Kettering institutional database.
It was found that multiorgan distant metastases confer poorer disease-specific survival in differentiated thyroid cancer. Cancer spread to individual organs occurred in 93 patients and multiorgan spread was observed in 32 patients. The TNM system is used to stage thyroid cancer. This system uses letters “A”, “B” and “C” to indicate how much the cancer has spread.
Staging is a way of describing where the cancer is found, if it has spread or where, and if it is affecting other parts of the body. In addition to this system, papillary and follicular thyroid cancers are also staged based on the patient's age. A radical approach to treating advanced cases would involve total thyroidectomy and partial laryngopharyngectomy. The absence of retropharyngeal and central compartment lymphadenopathy and the predominant nodal spread to the lateral compartment (levels II, III, IV) is also an argument against this.
In some cases, a thyroidectomy attempt may fail due to extensive extra thyroid infiltration of the tumor.