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Thyroid Cancer

  • What is Thyroid Cancer?

    Thyroid cancer is cancer affecting the thyroid, a butterfly-shaped gland at the base of the neck that produces hormones that regulate your heart rate, blood pressure, body temperature and weight. It is the 8th most common cancer affecting women in Singapore.

    infographic showing a cancerous thyroid and a healthy thyroid

    Types of thyroid cancers

    Thyroid cancers are classified according to their cell types

    • Papillary thyroid cancer – This is the most common form arising from thyroid follicles.
    • Follicular thyroid cancer – Also rises from thyroid follicles. May be difficult to differentiate from non-cancerous thyroid nodules.
    • Medullary thyroid cancer – This is an uncommon form of cancer that arises from cells located between thyroid follicles.
    • Anaplastic thyroid cancer – While uncommon, this form is aggressive and carries a poorer prognosis.
    • Thyroid lymphoma – A rare form of cancer.

    Causes

    Thyroid cancer may affect both the young and old. While everyone dreads being diagnosed with any form of cancer, thyroid cancers in general are readily treatable and carry very good prognoses, particularly in younger persons.

    Mutations of certain genes have been identified to cause papillary and follicular thyroid cancer. Unfortunately, the causative reasons for these gene mutations are not entirely clear. Excessive exposure to radiation is a well-established cause. Certain inherited medical conditions such as familial polyposis and Type 2 Multiple Endocrine Neoplasia (rare) are associated with thyroid cancers as well.

  • Signs & Symptoms

    lump in throat

    You may be at risk if you have a family history of thyroid cancer, or if you have previously been diagnosed with one of the above rare familial conditions. But, by and large, the majority of cases are sporadic in nature. They often present as a visible lump in the neck or are incidentally discovered as thyroid nodules on imaging done for other reasons. While most such lumps or nodules are non-cancerous, the possibility of thyroid cancer must be considered if they occur in the very young or the elderly, the nodule is rapidly enlarging, there is weight loss, hoarseness of voice or presence of enlarged lymph nodes in the neck.

  • Diagnosis & Assessment

    anatomy of a cancerous thyroid gland

    You should see an endocrinologist (hormone specialist) for assessment. Every thyroid lump or nodule should be evaluated by ultrasound, which is inexpensive, safe and easily available. Ultrasound allows doctors to accurately measure the size of a nodule. Certain sonographic features may help to differentiate between benign and cancerous nodules. Nodules that are small (below 1cm), well-defined or contain mostly fluid are likely benign. Hypoechoic nodules that appear tall with irregular borders, microcalcifications, hypervascularity and exceed 4cm with enlarged lymph nodes are more likely to be cancerous. Thyroid function and thyroid antibodies should also be assessed through blood tests as higher levels of thyroid stimulating hormone and antibodies are associated with a greater likelihood of cancer.

    Determining if a thyroid nodule is cancerous

    All nodules exceeding 1cm should be biopsied. This is very helpful in determining whether a nodule is benign or cancerous. This procedure may be easily performed by an experienced radiologist or endocrinologist in the clinic. Using ultrasound to visualise the nodule, a very fine needle is inserted into the nodule to draw out cells, which are then spread onto a slide and examined under a microscope. This procedure is known as Fine Needle Aspiration (FNA). No anaesthesia is required as the patient will only experience minor discomfort, superficial bleeding and mild bruising, if at all. The whole procedure should be completed within a few minutes. The result is classified into 6 categories (the Bethesda system) ranging from benign to cancerous. Should the result be indeterminate, a repeat FNA should be performed. Nodules that are benign need not be removed; they only need to be assessed annually with an ultrasound and possibly an FNA to monitor for any changes. The likelihood of a benign nodule becoming cancerous is very low.

  • Treatment & Care

    The patient should be ‘staged’ to determine the extent of the disease. Stage 1 is the earliest stage with the best prognosis while Stage 4 carries the least favourable prognosis. Special scans such as radionuclide scans are utilised for staging. Age is the most important determinant of stage, as persons below 45 years at the time of diagnosis usually has early stage disease. Other determinants include the size of the tumour and the extent of spread.

    thyroid disease sign

    Surgical excision of the entire thyroid gland, including the surrounding lymph nodes in the neck, is the preferred option. This carries the best chance for cure, particularly in persons with early stage disease, and surgery may be the only treatment necessary for this group of people. Removal of the entire thyroid gland also allows the endocrinologist to monitor for any possible recurrence by measuring the blood levels of thyroglobulin, which ought to be undetectable if thyroid cancer has been eradicated. Surgery is also the treatment of choice for medullary thyroid cancer and thyroid lymphoma.

    Following surgery, persons with papillary or follicular thyroid cancer greater than 1cm should receive radioiodine treatment about 4 weeks later. This is usually just a 1-time treatment where the patient drinks a small quantity of solution laced with radioactive iodine. As only thyroid cells assimilate iodine, this treatment will not harm other organ systems in the body. Radioiodine removes any remaining thyroid tissue that may still be present after surgery.

    After radioiodine treatment, a whole-body radionuclide scan is performed to ascertain that there is no remaining viable thyroid tissue in the body, following which the patient will have to start on lifelong thyroid hormone replacement. Thyroxine replacement serves to provide thyroid hormones for our bodily needs, and also helps to prevent thyroid cancer from recurring. Your endocrinologist will help to fine-tune and adjust the dosing appropriate for you. Patients with no evidence of disease recurrence only need to have their serum thyroglobulin and thyroid function checked every 6 months.

    Patients with advanced or recurrent disease may require additional doses of radioiodine. Radioiodine is not useful in medullary thyroid cancer and thyroid lymphoma. External beam radiation, chemotherapy and targeted therapy with tyrosine kinase inhibitors may be necessary for such cases.

    Information kindly provided by Dr Richard Chen, Consultant Endocrinologist, Gleneagles Hospital.