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Papillary thyroid cancer

Papillary thyroid cancer (PTC) is three times more likely in women than in men. It accounts for 80% of the thyroid cancers in adults. The tumor is generally slow growing and may have exist for decades prior to diagnosis. 


Risk factors

Your endocrinologist will review your history to determine if you have risk factors for the development of thyroid cancer. Radiation exposure during childhood is the most important risk factor for the development of differentiated thyroid cancer. Potentially sources of radiation include use of radiation for treating childhood cancers, or environmental exposure to atomic weapons or nuclear power plant accidents. Family history of thyroid cancer in a first degree relative (mother, father, brother, sister) or a cancer syndrome (family polyposis, Carney complex, multiple endocrine neoplasia type 2, Cowdens syndrome) increase the risk that a thyroid nodule may contain cancer. There is an increased risk of cancer if a patient notices rapid growth of a thyroid nodule or fixation of the nodule to surrounding tissues, new onset hoarseness, vocal cord paralysis, or the presences of abnormal appearing lymph nodules in the neck on the same side as a suspicious nodule. 

Clinical presentation

In the past, patients with thyroid cancers were found when a physician felt an abnormal thyroid on physical examination. Since the advent of more accessible imaging of non-thyroid structures, many non-palpable thyroid nodules are being found incidentally. Regardless of how discovered, the diagnosis can be determined by fine needle aspiration biopsy

Causes

Mutations or rearrangements in the genes encoding for proteins in the MAPK pathway seem to be part of the cause of differentiated thyroid cancers. This is an evolving field of research. In some series of patients, as many as 70% of well differentiated thyroid cancer have activation mutations in ret/PTC, NTRK1, Ras, or BRAF.  In mouse models, substances which activate these genes, result in the creation of thyroid cancer. Tumors that have a BRAF mutation may be more aggressive with higher rates of metastases and recurrence. 

Prognosis

Most patients with PTC do not die of their disease. In one study (1) with a median followup of 16 years, the patients likelyhood of death directly from the cancer in patients without metastases was only 6%. The features of PTC that imply a higher risk of recurrence and cancer related mortality are age greater than 45 at time of diagnosis, increasing size of the tumor, and presence of soft tissue invasion or distant metastases. Patients diagnosed between the ages of 20 and 45 years of age have the best long term prognosis; in a 30 year follow up period there was no effect on survival for patients less than 45 years at diagnosis. When tumors are small the patient has an excellent prognosis. There are currently a couple of staging systems used to help with prognosis and treatment. Specific molecular tools are being investigated to help with prognosis. 

Variants

Follicular variant of PTC is 10% of PTC cases. 
Tall cell variant is a more aggressive form of PTC and account for about 1% of PTC cases. 



References
1. Long-term impact of initial surgical and medical therapy on papillary and follicular thyroid cancer. Mazzaferri EL, Jhiang SM. Am J Med. 1994;97(5):418.
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