Thyroid cancer is a cancer originating from follicular or parafollicular thyroid cells (Pic. 1) within the thyroid gland. Thyroid cancer is the most prevailing endocrine malignancy, and its incidence presents a growing tendency during the last decades in the all world. The thyroid gland presents a wide spectrum of tumors derived from follicular cells that range from well differentiated, papillary and follicular carcinoma, usually carrying a good prognosis, to the clinically aggressive, poorly differentiated and undifferentiated thyroid carcinoma.
Thyroid cancers have been shown to be more prevalent in women than in men with a 3:1 ratio, and are usually diagnosed in the fourth to fifth decade of life. The most common presentation of thyroid cancers is an asymptomatic mass felt in the neck.
According to the histological features the thyroid cancers are divided into:
Papillary thyroid carcinoma (Pic. 2) is the most common thyroid cancer; this cancer presents relatively low malignancy, good prognosis, and a 10-year survival rate of over 90 %. The cancer arises from follicular cells, which produce and store thyroid hormones. It occurs more frequently in women and presents in the 20–55 year age group.
Follicular thyroid carcinoma (Pic. 3) accounts for 10–20 % of differentiated thyroid carcinomas, and it is the second malignant tumor originating from the follicular cells of the thyroid. FTC is defined by the presence of capsular and/or vascular invasion and by the absence of nuclear features typical of papillary thyroid carcinoma (PTC). FTC is more likely to metastasize to distant organs rather than to regional lymph nodes because of its tendency to invade blood vessels thus resulting in hematogenous dissemination. It usually affects people older than age 50.
Medullary thyroid carcinoma (Pic. 4) is a rare malignancy that arises from calcitonin-producing C-cells (parafolicullar cells) and frequently metastasizes to lymph nodes in the neck. Distant metastases may involve bone, lung, and liver. MTC accounts for as much as 5%–10% of all thyroid malignancies and as much as 13% of all thyroid cancer-related deaths.
Anaplastic thyroid carcinoma (Pic. 5) is rare, representing only 1-2% of all thyroid cancers, but nevertheless accounts for up to 50% of all thyroid cancer deaths. Survival time is generally short with one-year survival rates being reported at 10–20%. Long-term survival is rare and can lead to doubts about diagnosis. ATC typically occurs in adults age 60 and older.
Thyroid lymphoma is a relatively rare disease of the thyroid gland. It represents approximately 1%-5% of thyroid malignancies and less than 2% of extra nodal lymphomas: the prognosis is generally good. Thyroid lymphomas are more common in women with a predominance of 3-4:1.
After the discovery of a thyroid nodule by palpation or incidentally by imaging method the diagnosis of thyroid cancer is made on the basis of a biopsy by fine needle aspiration or after the nodule removal by surgery. Imaging tests (Pic. 6) may be done for a number of reasons, including helping find suspicious areas that might be cancer, to learn how far cancer may have spread, and to help determine if treatment is working.
Generally, 85% of patients with differentiated thyroid carcinomas are cured with surgery (Pic. 7), radioactive iodine, and thyroid-stimulating hormone (TSH) suppression. Of those that recur, the vast majority will recur in the neck, and best treatment options are surgical with potential further radioactive iodine. A small percentage of patients will develop or present with metastases and are more difficult to treat. When metastases have radioiodine avidity, prognosis is better, and further radioactive iodine may be used. However, when multiple doses of radioactive iodine have been tried or the patient has nonradioactive iodine avid disease, other options need to be considered.
Metastasis of thyroid cancers represents the main complication. In case of differentiated types of thyroid cancers, it is less probable to happen, as they are less aggressive. Due to alteration of hormonal balance within the bade, fertility potential is usually also reduced.
Despite treatment, thyroid cancer can return, even after thyroidectomy (removal of the thyroid gland; Pic. 8). Complications specific to thyroid surgery include injury to the recurrent laryngeal nerves, causing hoarseness and dysphagia (difficulty in swallowing), and injury to the parathyroids causing hypocalcemia (low blood calcium levels). Both complication types are considered permanent if they persist beyond six months postoperatively. Since thyroid cancer is unlikely to kill the patient, a permanent complication translates into lifelong, life-changing complications. Patients suffering permanent recurrent laryngeal nerve injury will have chronic problems with communication, swallowing, and aspiration often necessitating procedures like vocal cord injection and/or medialization. These complications, while specific to thyroidectomy, really do not reflect oncologic outcomes specific to thyroid cancer since they can occur regardless of the indication for thyroidectomy.
The main risk factors for thyroid cancer are:
Genetic factors are also included emphasizing:
It is not clear what causes most cases of thyroid cancer, so there's no way to prevent thyroid cancer in people who have an average risk of the disease.
In the case of family history of MTC, blood testcan be done to look for the gene mutations found in familial MTC. Thus, most of the cases of familial MTC can be prevented and treated early by removing the thyroid gland to prevent cancer.
As in case of any other cancers, thyroid cancers are also connected with (lower or higher) chances of metastasis plus the cancer treatment is most often detrimental for the function of gonads (ovaries or testicles) making the conception impossible.
Therefore, a cryopreservation of generative cells (sperm cells and oocytes) should be considered to preserve the fertility. Cryopreservation involves the storage of reproductive cells (oocytes and sperm cells) within carbon dioxide ensuring extremely low temperatures to prevent cell ageing.
Differentiated thyroid carcinoma (papillary and follicular) has a favorable prognosis with an 85% 10-year survival. The patients that recur often require surgery and further radioactive iodine to render them disease-free. Women have a short-term decrease in fertility in the first three to six months after radioactive iodine treatment and often have irregular menstrual bleeding during that time period. For some women, irregular periods may last up to a year after treatment. Women receiving radioactive iodine therapy are strongly encouraged to avoid pregnancy for at least six months and, ideally, one year after treatment. In men, an impairment of fertility potential is already present after treatment, the option of freezing semen should be considered.
Despite the generally good prognosis of thyroid carcinoma, about 5% of patients will develop metastatic disease which fails to respond to radioactive iodine, exhibiting a more aggressive behavior. These patients will die of their disease.
Prognosis of anaplastic carcinoma is poor, regardless of therapy. Therapeutic options currently for anaplastic thyroid carcinoma are limited and have not proven effective. Surgical debulking of tumors followed by chemoradiotherapy is most affective against localized tumors. Unfortunately, anaplastic cancer often presents as more advanced, extracapular, metastatic disease.