About thyroid neoplasia (thyroid cancer)
Tumours of the thyroid gland can be benign or malignant. Typically, thyroid malignancies present as a single nodule on the thyroid gland. Any patient presenting with a solitary thyroid nodule needs to investigate it thoroughly to rule out malignancy. However, malignant tumours of the thyroid gland are rare, accounting for around 5% of thyroid lumps. Even when malignancy is present, these tumours usually have an excellent prognosis.
Risk Factors
The single most important risk factor for thyroid neoplasia is a history of radiation to the head and neck. This is of greater significance if the exposure occurred prior to the age of 20. Other risk factors for thyroid neoplasia include:
- Smoking
- History of certain benign thyroid diseases, such as benign nodules, thyroiditis and multinodular goitre
- Family history of thyroid cancer
- Familial adenomatous polyposis – a condition which greatly increases the chance of developing bowel cancer
Benign or Malignant?
There are a few features relating to a patient’s presentation which may increase the suspicion that a thyroid nodule is malignant. These are not definitive signs of malignancy – the only way of definitively determining whether a thyroid nodule is benign or malignant is by taking a biopsy. Some features which may suggest malignancy include:
- “Cold nodules”. These are nodules which do not take up as much radioactive iodine as other parts of the thyroid gland in a nuclear medicine scan
- Patients aged younger than 30 or older than 60
- A solitary nodule
- A hard, firm nodule
- Male patients – a nodule in a male patient is more likely to be malignant than a nodule in a female patient
There are also symptoms which the patient may experience that also suggest a malignancy. These include:
- A painless lump in throat
- Change in the character/quality of voice
- Fast rate of growth
Follicular Adenoma
Follicular adenomas are derived from the follicular cells of the thyroid. The follicular cells are epithelial cells within the thyroid gland which are involved in the secretion and production of the thyroid hormones, T3 and T4. Follicular adenomas are benign; however, it can be difficult to differentiate them from a follicular carcinoma or hyperplastic nodules as they present similarly. They also have similar appearances under the microscope. Follicular adenomas are cold nodules on a thyroid scan, whereas toxic adenomas will be hot nodules.
In most instances, follicular adenomas are non-functional and do not produce any thyroid hormones. However, in some cases, follicular adenomas may produce a large quantity of thyroid hormones and present with symptoms of thyrotoxicosis. These are called toxic adenomas.
Microscopically, a follicular adenoma may look similar to the normal thyroid tissue. There follicular cells are arranged into a follicular pattern on the whole; however, the follicles have less colloid cells than normal and are not as well organised. The nuclei of the adenomatous cells are large exhibit an increased nucleus to cytoplasm ratio. Follicular adenomas are surrounded by a connective tissue capsule which helps to demarcate it from normal thyroid tissue. The normal, surrounding thyroid tissue is usually compressed by the adenoma. In some adenomas, there are microscopic signs of haemorrhage, calcification, fibrosis (scarring) and cysts. Some follicular adenomas have cells which possess granules in their cytoplasm; these cells are called Hurthle cell adenomas.
Follicular adenomas are typically painless nodules, and are often discovered as an incidental finding on a physical examination. Larger nodules may be symptomatic if they lead to compression and obstruction of underlying structures, such as the trachea and oesophagus. Diagnosis is made based on the histopathological characteristics of a biopsy.
Follicular Carcinoma
Follicular carcinomas account for approximately 15% of all thyroid carcinomas. These are malignant tumours which have a similar histological profile to follicular adenoma with one key difference. A follicular carcinoma, by definition, will invade the connective tissue capsule surrounding the nodule. They may also invade the surrounding vasculature or surrounding normal thyroid tissue.
Follicular carcinomas tend to be more prevalent in areas of endemic iodine deficiency and have a high incidence amongst middle aged adults. On nuclear medicine scans, follicular carcinomas are typically cold nodules. Follicular carcinomas do not usually metastasise to the lymph nodes; instead they spread by the blood to other organs, such as the bones, lungs and the liver.
Papillary Carcinoma
Papillary carcinomas are the most common form of thyroid carcinoma, accounting for up to 85% of all thyroid carcinomas. They tend to present as a painless nodule in the neck. Papillary carcinomas are rarely functional and hence do not secrete thyroid hormones. Papillary carcinomas tend to spread via the lymph nodes, and sometimes metastases are found in the lymph nodes of the neck. However, even with spread to the regional lymph nodes, there are excellent ten-year survival rates. Papillary carcinomas are the most common carcinomas seen in patients with a history of ionising radiation to the head and neck region. They are commonly found in patients between the ages of 20 and 40; however, they can present at any age.
Papillary carcinomas have different histological features to follicular carcinoma. There may be one or more nodules present in the gland. In general, papillary carcinomas tend to invade the surrounding thyroid tissue. Some cases, however, have connective tissue capsules and are well circumscribed. The nuclei of the cells are clear, an appearance known as “orphan Annie eye”. Others have a “coffee bean” appearance. The tumours often have a fibrovascular core. The amount of colloid in the tumour is also sparse. Another histological feature is the psammoma body; which is a calcified structure seen in some histological specimens.
Medullary Carcinoma
Medullary carcinomas are tumours of the C cells (or parafollicular cells), which secrete the hormone calcitonin, which is released when there are high blood levels of calcium. This causes deposition of calcium into the bones. The levels of calcitonin in the bloodstream are commonly measured as part of the diagnosis of this tumour. About 1/5th of medullary carcinomas have a familial basis, and can occur as part of multiple endocrine neoplasia syndromes (MEN 2A or 2B). Patients with the MEN 2A/2B syndromes tend to develop the tumours in early adulthood, and sometimes even during adolescence and childhood.
Medullary carcinomas tend to present as either one or multiple masses in the neck. Cases associated with MEN 2A/2B tend to have multiple tumours within the thyroid gland. Larger tumours can present with obstructive symptoms, such as difficulty swallowing or voice changes. Despite elevated levels of calcitonin, patients do not usually have pathologically low levels of blood calcium (hypocalcaemia). Microscopically, medullary carcinomas have a characteristic deposition of amyloid plaques (collections of proteins outside of the cell). The morphology of the cells is variable. Some tumours have a follicular pattern, whereas others have a trabecular pattern. Special stains can be applied to the biopsy, which stain the calcitonin being secreted by the tumour. Familial carcinomas also tend to show hyperplasia of the C cells in the surrounding normal thyroid tissue.
Anaplastic Carcinoma
Anaplastic thyroid carcinomas generally have a worse prognosis and are very aggressively growing tumours. The aggressive growth rate means that patients often exhibit obstructive and compressive symptoms, such as difficulty swallowing, stridor and voice changes. The tumour may often grow beyond the normal distribution of the thyroid gland into other neck structures. The cells of an anaplastic thyroid carcinoma exhibit no differentiation. Anaplastic carcinomas are more common in elderly patients. Many patients found to have an anaplastic carcinoma tend to report a previous history of another thyroid disorder, including multinodular goitre or other type of carcinoma. Some patients have another form of differentiated thyroid carcinoma (follicular, medullary or papillary) at the same time as the anaplastic tumour. This suggests that anaplastic carcinomas may arise from other thyroid carcinomas. Microscopically, the following may be seen in an anaplastic carcinoma:
- Spindle cells
- Giant cells
- Mixed spindle and giant cells
- Small cells
Diagnosis
If you have a lump in your thyroid gland that could be thyroid cancer, your doctor may do a biopsy to check for cancer cells. A biopsy is a simple procedure in which a small piece of the thyroid tissue is removed, usually with a needle, and then checked.
Sometimes the results of a biopsy are not clear. In this case, you may need surgery to remove the lump to find out if you have thyroid cancer.
If you have questions about thyroid cancer make an appointment to see our thyroid surgeon.
