Carcinoma of the thyroid gland is an uncommon cancer, but is the most common malignancy of human endocrine system. Differentiated tumors, whether those are papillary or follicular, are highly treatable and are usually curable. Poorly differentiated tumors such as medullary or anaplastic are much less common. These tumors are aggressive, metastasize early, and have a much poorer prognosis. Thyroid cancer affects women more often than men and usually occurs in people between the ages of 25 and 65 years old. The incidence of this malignancy has been increasing over the last decade, and thyroid cancer commonly presents as a cold nodule. The overall incidence of cancer in a cold nodule is 12% to 15%, but it is higher in people younger than 40 years.What is follicualr thyroid carcinoma
Follicular carcinomas are the second most common thyroid cancers. Follicular carcinoma is considered more malignant and aggressive than is papillary carcinoma. It occurs in a slightly older age group than papillary. This kind of cancer is also less common in children. In contrast to papillary cancer, it occurs only rarely after radiation therapy, and mortality is related to the degree of vascular invasion. Age is a very important factor in terms of prognosis for folicular thyroid carcinoma. Patients over 40 have a more aggressive disease and typically the tumor does not concentrate iodine as well as it is in younger patients. Vascular invasion is characteristic for follicular carcinoma and therefore distant metastasis is much more common. Distant metastasis may occur in a small primary, where lung, bone, brain, liver, bladder, and skin are potential sites of distant spread. Lymph node involvement is far less common than in papillary carcinoma.
Risk factors
Patients with a history of radiation administered in infancy and childhood for benign conditions of the head and neck, such as enlarged thymus, acne, or tonsillar or adenoidal enlargement, have an increased risk of cancer.
These patients have increased risk for some other abnormalities of the thyroid gland as well. In this group of patients, malignancies of the thyroid gland first appear beginning as early as 5 years following radiation and may appear 20 or even more years later. Radiation exposure as a consequence of nuclear fallout has also been associated with a high risk of thyroid cancer, and this consequence is especially high in children. Other risk factors for the development of thyroid cancer include a history of goiter, family history of thyroid disease, female gender, and sometimes Asian race.
Causes of thyroid cancer
Everyone is susceptible to thyroid cancer, but thyroid gland is particularly sensitive to the effects of ionizing radiation. Exposure to ionizing radiation results in a 30% risk for thyroid cancer, while a history of exposure of the head and neck to x-ray beams, especially during childhood, has been recognized as an important contributing factor to the development of all kinds of thyroid cancers. For example, 7% of the individuals exposed to the atomic bomb in Japan developed thyroid cancer later in life. Therapeutic irradiation of body areas was used to treat tumors and benign conditions, such as acne, excessive facial hair, tuberculosis in the neck, fungus diseases of the scalp, sore throats, chronic coughs, and enlargement of the thymus, tonsils, from the 1920s to the 1960s. About 10% of these individuals who were treated with irradiation developed thyroid cancer after 30 years of latency period. Patients who need radiotherapy for certain types of cancer of the head and neck area may have an increased risk of developing thyroid cancer as well. However, exposure to diagnostic x-rays does not increase the risk of developing thyroid cancer. Although follicular cancer is frequently present in goitrous thyroids, the relationship between prolonged elevation of thyroid-stimulating hormone and follicular carcinoma is not known. In the same time, several reports have shown a relationship between iodine deficiency and the incidence of thyroid carcinoma. Incidence of folicular thyroid cancer has decreased in geographic areas of endemic goiter where the iodination of salt was instituted. Some studies demonstrate that mutations of the ras oncogene could be implicated in the neoplastic transformation of thyrocytes in folicular thyroid cancer. N-ras and h-ras mutations should be the first events in the pathogenesis of folicular thyroid cancer, followed by several further mutations. Some molecules that physiologically regulate the growth of the thyrocytes, as interleukins or other cytokines could play a role in the pathogenesis of the FTC.
Medical care after surgery
About five weeks after surgical thyroid removal, patients must have radioiodine to detect and destroy any metastasis and any residual tissue in the thyroid. Patients will probably take thyroid replacement therapy for life, especially after total thyroidectomy. This entails taking 2.5-3.5 mcg/kg of L-T4 every day of their life. A number of indications for external beam radiation apply to the management of folicular thyroid cancer. If all gross disease cannot be resected, or if residual disease is not avid for radioactive iodine, external beam radiation therapy often is employed for locally advanced disease. Similarly, radiation is indicated for unresectable disease extending into adjacent structures, such as the trachea, esophagus, great vessels, mediastinum, and connective tissue. In this situation, radiation doses of 6000-6500 cGy typically are commonly used. Following RT for unresectable disease, the patient should undergo I-131 scanning, so if uptake is detected, a dose of I-131 should be administered as well. External beam radio therapy also may be used after resection of recurrent folicular thyroid cancer that is no longer avid for radioactive iodine. In the postoperative setting, radiation doses of 5000-6000 cGy commonly are delivered to the tumor bed to reduce the risk of local-regional recurrence. Careful treatment planning should be employed to minimize the risks of these radiation therapy complications. Finally, a palliative course of radiation is useful to relieve pain from common bone metastases. Chemotherapy with cisplatin or doxorubicin has limited efficacy, producing occasional objective responses and these responses are generally for short durations. Because of the high toxicity of chemotherapy with cisplatin or doxorubicin, it may be considered in symptomatic patients with recurrent or advancing disease, which could improve quality of life in patients with bone metastases. However, no standard protocol exists for chemotherapy of metastatic folicular thyroid cancer.
Prognostic factors
The prognosis for differentiated carcinoma is better for patients younger than 40 years. Prognosis is especially better for young people without extracapsular extension or vascular invasion. Age appears to be the single most important prognostic factor, while the prognostic significance of lymph node status is controversial. Adverse factors included age older than 45 years, follicular histology, primary tumor %26gt;4 cm, extrathyroid extension, and distant metastases. Regional lymph node involvement had no effect or even an adverse effect on patients survival. Diffuse, intense immunostaining for vascular endothelial growth factor in patients with papillary cancer has been associated with a high rate of local recurrence and distant metastases for most of the patients. Elevated serum thyroglobulin level correlates strongly with recurrent tumor when found in patients with differentiated thyroid cancer, during their postoperative evaluations. Serum thyroglobulin levels are most sensitive when patients are hypothyroid and have elevated serum thyroid-stimulating hormone levels and expression of the tumor suppressor gene p53 has also been associated with an adverse prognosis for patients with thyroid cancer. Patients considered to be low risk by the age, metastases, extent, and size risk criteria include women younger than 50 years and men younger than 40 years without evidence of distant metastases. Also included in the low-risk group are older patients with primary tumors %26lt;5 cm and papillary cancer without evidence of gross extrathyroid invasion or follicular cancer without major capsular invasion or blood vessel invasion. The fact is that thyroid gland may occasionally be the site of other primary tumors, including sarcomas, lymphomas, epidermoid carcinomas, and teratomas and may be the site of metastasis from other cancers. These metastaese are particularly of the lung, breast, and kidney.
What about thyroid hormone pills after thyroid cancer surgery?
Regardless of whether a patient has just one thyroid lobe and the isthmus removed, or the entire thyroid gland removed, most experts agree they should be placed on thyroid hormone. As you could already hear, it is recommended to use for the rest of their lives. This is to replace the hormone in those who have no thyroid left, and to suppress further growth of the gland in those with some tissue left in neck. There is good evidence that follicular carcinoma responds to thyroid stimulating hormone secreted by the pituitary. Therefore, exogenous thyroid hormone is given which results in decreased TSH levels and a lower impetus for any remaining cancer cells to grow, where recurrence and mortality rates have been shown to be lower in patients receiving suppression.
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