Thyroid cancer refers to cancer that develops within the thyroid, a gland found at the front of the neck. The thyroid produces hormones that help control certain processes in the body such as heart rate, digestion, body temperature and weight.

The thyroid is primarily made up of two types of cells:

• Follicular cells – these produce and store the hormones T3 (triiodothyronine) and T4 (thyroxine) and the protein Tg (thyroglobulin)
• Parafollicular cells (C-cells) – these produce the hormone calcitonin, which helps control calcium levels in the body

Thyroid cancer is often differentiated by the type of cell the cancer develops from.

The four types of thyroid cancer include:

• Papillary thyroid cancer – slow-growing cancer that develops from the follicular cells in the thyroid. This is the most common type of thyroid cancer, accounting for 70-80% of all thyroid cancer diagnoses
• Follicular thyroid cancer – cancer that also develops from the follicular cells in the thyroid. This accounts for 15-20% of all thyroid cancer cases and includes Hürthle cell carcinoma
• Medullary thyroid cancer – an often hereditary cancer that develops from the parafollicular cells in the thyroid. This accounts for 4-5% of all thyroid cancer diagnoses and can be associated with tumours in other glands
• Anaplastic thyroid cancer – rare fast-growing cancer that develops from the follicular or parafollicular cells in the thyroid. This accounts for 1-2% of all thyroid cancer cases and typically occurs in people over the age of 60

Thyroid cancer is the eighth most common cancer in Singaporean women and 13^th most common cancer across Singapore.

Thyroid cancer can be described in stages depending on how early or advanced the cancer is.

The TNM system is used to stage thyroid cancer and helps doctors understand what your cancer looks like. TNM stands for:

• Tumour – the degree to which the tumour has affected other tissue.
• Node – is a measure of whether lymph nodes have been affected.
• Metastasis – the degree to which the cancer has spread to other organs of the body.

The TNM information, along with other tests helps determine the stage of your thyroid cancer.

Papillary and follicular thyroid cancer (only Stage I and Stage II apply to those under 55 years of age):

• Stage I – the cancer is no larger than 4 cm and confined to the thyroid. For those under 55, the cancer may be any size and might or might not have spread to nearby lymph nodes.
• Stage II – the cancer is no larger than 4 cm across and confined to the thyroid, but has spread to nearby lymph nodes. For those under 55, the cancer may be any size and has spread to other areas of the body such as distant lymph nodes, internal organs or bone.
• Stage III – the cancer may be any size and has spread to nearby tissue such as the larynx, trachea or oesophagus. It might or might not have spread to nearby lymph nodes.
• Stage IVA – the cancer may be any size and has spread extensively beyond the thyroid toward the spine or into nearby large blood vessels. It might or might not have spread to nearby lymph nodes.
• Stage IVB – the cancer is any size and might or might not have spread to nearby lymph nodes, but has spread to distant areas of the body such as lymph nodes, internal organs or bone.

Anaplastic thyroid cancer (all anaplastic thyroid cancers are considered Stage IV):

• Stage IVA – the cancer is any size and confined to the thyroid.
• Stage IVB – the cancer is any size and confined to the thyroid, but has spread to nearby lymph nodes. Alternatively, the cancer is any size and has grown into the strap muscles around the thyroid, but might or might not have spread to nearby lymph nodes.
• Stage IVC – the cancer is any size and might or not have spread to nearby lymph nodes, but has spread to distant areas of the body such as lymph nodes, internal organs or bone.

Medullary thyroid cancer:

• Stage I – the cancer is no larger than 2 cm and confined to the thyroid.
• Stage II – the cancer is no larger than 4 cm across and confined to the thyroid. Alternatively, the cancer is larger than 4 cm and confined to the thyroid, or any size and growing outside of the thyroid but not involving nearby structures.
• Stage III – the cancer is any size and may be growing outside of the thyroid but not involving nearby structures. It has spread to lymph nodes in the neck.
• Stage IVA – the cancer is any size and has grown into nearby tissues in the neck, such as the larynx, trachea or oesophagus. It might or might not have spread to nearby lymph nodes. Alternatively, the cancer is any size and might be growing outside of the thyroid, but has spread to certain lymph nodes in the neck.
• Stage IVB – the cancer is any size and has grown toward the spine or into nearby large blood vessels, but might or might not have spread to nearby lymph nodes.
• Stage IVC – the cancer is any size and might have grown into nearby structures or lymph nodes, but has spread to distant areas of the body such as the liver, lung, bone or brain.