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Medullary thyroid carcinoma (MTC) is a special type of thyroid cancer distinct from differentiated thyroid cancers. This cancer starts in the parafollicular C cells of the thyroid gland. These cells make a hormone called calcitonin. Calcitonin is not made from iodine unlike other thyroid hormones.
MTC is very rare in children. Most often, pediatric MTC is associated with a genetic predisposition: familial MTC or type 2 multiple endocrine neoplasias (MEN syndromes).
Hereditary or familial MTC is caused by a germline mutation of the RET gene. RET gene mutations can also lead to multiple endocrine neoplasia (MEN). These conditions affect the endocrine system and may include pheochromocytoma and hyperparathyroidism. The specific type of mutation can influence the management of MTC and related health conditions. Family members of patients with RET mutations should receive genetic counseling and testing.
The main symptom of thyroid cancer is a nodule, or lump, in the thyroid gland. Sometimes, lymph nodes in the neck will appear swollen. Other possible symptoms include problems breathing, difficulty or pain swallowing, and hoarseness. However, often thyroid cancer does not cause any symptoms and may be found as part of a routine exam.
In children, medullary thyroid cancer is most often seen as part of a genetic syndrome. In certain cases, the thyroid gland may be removed before there are any signs of cancer as a way to prevent MTC.
Doctors test for thyroid cancer in several ways. These tests include:
The stage, or extent of disease, of medullary thyroid cancer depends on the size of the tumor and whether the cancer has spread to lymph nodes or other parts of the body.
|Stage||Extent of disease|
|Stage 1||Tumor is 2 centimeters or less across and limited to the thyroid. There is no spread of disease.|
|Stage 2||Tumor is larger than 2 centimeters across. It is primarily limited to the thyroid with no spread to lymph nodes or other sites.|
|Stage 3||The tumor may have grown slightly outside the thryoid gland, and there is spread of disease to nearby lymph nodes in the neck.|
|Stage 4||There is evidence of morderate or advanced disease. The tumor has spread beyond the thyroid into other tissue; there is spread to regional lymph nodes; and/or the tumor has spread to distant sites.|
In children with known predisposition to have MTC, a major goal is to plan for safe removal of the thyroid before MTC develops, and particularly before distant spread of MTC. Prognosis is related to the extent (stage) of disease.
Factors that influence prognosis include:
A multidisciplinary team is needed for the evaluation and treatment of medullary thyroid cancer (MTC). Care decisions are focused on survival while lowering risk of continued disease and unwanted treatment effects. Because of the risk of recurrence and other considerations (e.g., hormone function, secondary cancers, genetic predisposition), long-term follow-up is needed for all patients. Total thyroidectomy to remove the thyroid gland is the recommended treatment for MTC. Unlike differentiated thyroid cancers, medullary thyroid cancer does not take up iodine. Therefore, radioactive iodine is not used for imaging and treatment of MTC. After surgery to remove the thyroid, patients need lifelong thyroid hormone replacement medication (levothyroxine). TSH is monitored and maintained in normal range. TSH suppression is not needed in medullary thyroid cancer.
Surgery to remove the thyroid gland (thyroidectomy) is the main treatment for medullary thyroid cancer. A total thyroidectomy is recommended. Complete removal of the thyroid helps to lower the risk of metastasis or continued disease. Neck dissection to remove lymph nodes and other tissues may also be performed to reduce the risk of recurrence. Assessment and care by a multidisciplinary pediatric team is important including a surgeon who is experienced in thyroid cancer surgeries.
Preventive Surgery for MEN Syndromes
The best chance of treating MTC is to prevent it from spreading. A prophylactic thyroidectomy is recommended for children with known genetic mutations. This means that the thyroid gland is surgically removed before cancer is detected because of the high risk of developing cancer. For children with a MEN2A mutation, prophylactic thyroidectomy is recommended before 5 years of age. Children with a MEN2B mutation should have a thyroidectomy before 1 year of age. MTC in patients with the MEN2B mutation has an early onset and is very aggressive.
Thyroidectomy should be done by an experienced surgeon who regularly performs these procedures on pediatric patients. Treatment guidelines recommend that surgery be performed by a high-volume thyroid surgeon who does at least 30 similar procedures each year. This reduces the risk of surgical complications. Risks of surgery include damage to structures in the neck region such as nerves and parathyroid glands.
Surgery to remove lymph nodes in the neck is called neck dissection. Central neck dissections are typically done when the primary thyroid tumor is larger than 4 cm or when the tumor has spread beyond the tissue that covers the thyroid gland (thyroid capsule).
Lateral neck dissections are most often done when the thyroid cancer has spread to the lymph nodes in the neck. Both types of neck dissections involve removing the lymph nodes that are most likely to communicate with the thyroid gland and are most likely to contain cancer cells which have spread.
Each individual has 4 parathyroid glands, which are very small structures located behind the thyroid and are responsible of maintaining normal levels of calcium in the body. Even in the absence of surgical damage, the parathyroid glands frequently get “stunned” after thyroidectomy; affected patients experience symptoms of low calcium (or hypocalcemia) including numbness and tingling in the hands, feet, and face and muscle cramps. Treatment requires the use of a potent form of vitamin D (calcitriol) and calcium supplementation until the resolution of this condition (“Transient post-surgical hypo-parathyroidism”). When the parathyroid glands are removed or permanently damaged, hypo-parathyroidism becomes permanent and patients require lifelong treatment for it.
Another risk of thyroid surgery is injury to the recurrent laryngeal nerve. This nerve allows the vocal cords to move and function for speech. Sometimes, the recurrent laryngeal nerve may have to be removed due to the tumor itself.
Before surgery, otolaryngologists typically perform a “scope” in the office to check vocal cord function. This procedure involves placing a flexible camera through the nose to visualize the vocal cords and to make sure that they are they are working properly. The procedure is repeated after surgery to evaluate vocal cord function.
To reduce the risk of injury to the nerve during surgery, a special endotracheal tube (breathing tube) can be used. This breathing tube has an electrode that detects and monitors the nerves during surgery.
If a vocal cord is injured during surgery, it is often temporary. However, it may take up to a year and a half to recover. If a patient has a change in voice or difficulty breathing or swallowing, the vocal cords can be injected with a temporary material to improve those functions. A re-innervation procedure may be needed if the nerve does not recover. This procedure connects the non-working recurrent laryngeal nerve with a working nerve to improve the function of the affected vocal cord.
These nerve complications due to thyroidectomy are rare and occur at a rate from 1.4% - 14%. The more experienced the surgeon, the lower the risk of complications.
Patients need lifelong monitoring and follow-up care by an interdisciplinary medical team after treatment for thyroid cancer. Specific recommendations for frequency and types of tests differ according to patient needs and thyroid cancer type and stage. Additional considerations include support for adherence to thyroid hormone replacement therapy.
Ongoing monitoring includes physical exams, measurement of calcitonin levels, and neck ultrasound. Patients should also be examined for signs of other cancers related to known genetic mutations.
Key Aspects of Long-Term Care:
Patients can benefit from psychosocial support during treatment and survivorship. Care team members representing Psychology, Child Life, Social Work, and other disciplines can assist with coping and adherence to treatments that may affect quality of life. Possible issues include adjustment to daily medication use, body image concerns due to surgical scars, and other adjustment needs.
Patients may also need physical therapy after surgery to assist with neck mobility and range of motion.
For general health and disease prevention, all cancer survivors should adopt healthy lifestyle and eating habits, as well as continue to have regular physical checkups and screenings by a primary physician at least annually.
Reviewed: June 2018