[4] Risk factors include radiation exposure at a young age, having an enlarged thyroid, family history and obesity.

Later symptoms that can be present are pain in the anterior region of the neck and changes in voice due to an involvement of the recurrent laryngeal nerve.

[16] Thyroid cancer is usually found in a euthyroid patient, but symptoms of hyperthyroidism or hypothyroidism may be associated with a large or metastatic, well-differentiated tumor.

[17] Thyroid cancers are thought to be related to a number of environmental and genetic predisposing factors, but significant uncertainty remains regarding their causes.

[18] Environmental exposure to ionizing radiation from both natural background sources and artificial sources is suspected to play a significant role, and significantly increased rates of thyroid cancer occur in those exposed to mantlefield radiation for lymphoma, and those exposed to iodine-131 following the Chernobyl,[19] Fukushima, Kyshtym, and Windscale[20] nuclear disasters.

[20][22] Genetic causes include multiple endocrine neoplasia type 2, which markedly increases rates, particularly of the rarer medullary form of the disease.

[10] After a thyroid nodule is found during a physical examination or incidentially on imaging, a referral to an endocrinologist or a thyroidologist may occur.

Various radiological clinical criteria, including the thyroid imaging reporting and data system (TI-RADs) score, are used to characterize the risk of malignancy.

[24] TI-RADS developed by the American College of Radiology (ACR) guides clinicians in deciding which nodules require fine-needle aspiration cytology (FNAC) and in planning follow-up.

[25] On ultrasound, nodules that are hypoechogenic (solid consistency), having irregular borders, increased vascularity, calcifications, or being taller than wide on transverse views are associated with malignancy.

To achieve a definitive diagnosis, a fine needle aspiration cytology test may be performed and reported according to the Bethesda system.

[29] After diagnosis, to understand potential for spread of disease, or for follow up monitoring after surgery, a whole body I-131 or I-123 radioactive iodine scan may be performed.

[33][34] These variants can be distinguished (distribution over various subtypes may show regional variation): The follicular and papillary types together can be classified as "differentiated thyroid cancer".

The tumor infiltrates into infrahyoid muscles, trachea, oesophagus, recurrent laryngeal nerve, carotid sheath, etc.

The tumor emboli do angioinvasion of lungs; end of long bones, skull, and vertebrae are affected.

[49] Thyroidectomy and dissection of central neck compartment is the initial step in treatment of thyroid cancer in the majority of cases.

[14] Thyroid-preserving operations may be applied in cases, when thyroid cancer exhibits low biological aggressiveness (e.g. well-differentiated cancer, no evidence of lymph-node metastases, low MIB-1 index, no major genetic alterations like BRAF mutations, RET/PTC rearrangements, p53 mutations etc.)

[52] Post surgical monitoring for recurrence or metastasis may include routine ultrasound, CT scans, FDG-PET/CT, radioactive iodine whole body scans, and routine laboratory blood tests for changes in thyroglobulin, thyroglobulin antibodies, or calcitonin, depending on the subtype of thyroid cancer.

[14] External irradiation may be used when the cancer is unresectable, when it recurs after resection, or to relieve pain from bone metastasis.

[59] Increasingly, small thyroid nodules are discovered as incidental findings on imaging (CT scan, MRI, ultrasound) performed for another purpose.

[10] RasGTPase mutations are seen in 13% of papillary and 25-50% of follicular cancers and are associated with increased risk of vascular invasion and higher response to radioactive iodine.