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 8^th most common cancer affecting women in Singapore.

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.

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.