Whereas benign thyroid nodules are very common, malignancy of the thyroid is rare, varied and generally treatable.
There are several predisposing factors for thyroid cancer. Familial or genetic risks are rare, but irradiation (some nuclear isotopes), such as following nuclear reactor or nuclear bombs is a potentiator, especially in children. Several geographic areas have high background irradiation. Thyroid treatment with I 131 (radioactive iodine) is not a risk factor.
The diagnosis of thyroid cancer is difficult and many are detected only after thyroidectomy for other reasons. There are different types and there are very few specific symptoms.
The most common is called "well differentiated" and has a very good prognosis. There is also a group of "poorly differentiated" cancers. These are less common and some, called the anaplastic carcinomas, are difficult and resistant to many treatments.
The other groups are the medullary cancers, which are rare and can run in families, and a diverse group of "others" including lymphomas and cancers which have spread to the thyroid (metastatic).
The therapy for all forms of thyroid cancer is multi-disciplinary and involves different experts, but the mainstay is surgery in the form of total thyroidectomy. Removal of the whole thyroid often cures the disease, but more importantly enables other therapy such as I 131 and monitoring for recurrence with blood tests.