Types of cancer

Thyroid

Thyroid cancer develops in the gland that is located at the front part of the neck and is responsible for the production of metabolism hormones. Exposure to radiation and a diet low in iodine are the main risk factors. Learn more.
5 min de leitura
por: Grupo Oncoclínicas
Thyroid
Thyroid cancer is the most common cancer of the head and neck region and affects three times more women than men.

What is Thyroid Cancer

The thyroid gland is located at the front of the neck, below the thyroid cartilage (Adam’s apple) and produces hormones that help regulate metabolism, heart rate, blood pressure and body temperature. Thyroid cancer forms when thyroid cells begin to grow and multiply uncontrollably.

It is the most common cancer of the head and neck region and affects three times more women than men.

The main risk factors for thyroid cancer are:

  • Radiation exposure – a proven risk factor for thyroid cancer. Sources of such radiation include some medical treatments and also radioactive fallout from power plant accidents or nuclear weapons;
  • Poor diet – follicular thyroid cancers are more common in areas of the world where people’s diets are low in iodine. Adding iodine to salt, common in many countries, prevents the disease.

It is worth pointing out that the presence of thyroid nodules is not always an indication of cancer, as most of these nodules are benign – only about 5% to 10% of thyroid nodules are cancerous. These nodules appear at any age, but are more common in older adults.

Thyroid Cancer Subtypes

Different types of cancer develop from each cell type in the region, which is important to detect because they impact the severity of the cancer and the treatment needed.

The main subtypes of thyroid cancer are:

  • Well-differentiated carcinomas – their cells look very similar to normal thyroid tissue when viewed in the lab. They develop from thyroid follicular cells and represent the majority of thyroid cancers. In general, they have little aggressive behavior and are highly responsive to iodine therapy.  Well differentiated carcinomas, in turn, aggregate three different subtypes: papillary (most frequent – 80% of the cases), follicular and Hurthle cell carcinoma;
  • Medullary carcinoma – it develops from the C cells of the thyroid gland, which normally produce calcitonin, a hormone that helps to control the amount of calcium in the blood. It is rare and shows slow growth and no responsiveness to iodine therapy;
  • Anaplastic carcinoma or undifferentiated carcinoma – is a rare form of thyroid tumor, representing about 2% of all cases. It is called undifferentiated because the cancerous cells do not resemble the normal thyroid cells. It is an aggressive cancer, with rapid and early growth, which compromises the structures of the neck. The prognosis is worse than the other subtypes.

Symptoms and signs of thyroid cancer

Often in small tumors, patients are asymptomatic. When they do manifest themselves, the main symptoms or signs of thyroid cancer are:

  • Nodule or lump (especially if they are fast growing);
  • Swelling in the neck;
  • Pain in the anterior part of the neck, sometimes radiating to the ears;
  • Persistent hoarseness or other voice changes
  • Difficulty swallowing
  • Breathing problems;
  • Constant coughing.

There are benign conditions that also cause symptoms like these, particularly the presence of nodules. Any of these signs requires seeking a doctor for a more detailed evaluation of the clinical picture.

Diagnosis of thyroid cancer

Physical examination and patient history are the first steps in detecting thyroid cancer.

After the suspicion, tests are used to confirm the neoplasm, including staging and defining the best course of treatment. Imaging tests are important because they help find suspicious areas that may be cancer and check whether the neoplasm has spread, which impacts the choice of treatment. The main ones are:

  • Ultrasound – is one of the first tests and helps determine whether a thyroid nodule is solid or cystic (fluid-filled) – solid nodules are more likely to be cancerous. It can also be used to check the number and size of nodules and help determine if any nearby lymph nodes have been affected by cancer. Also, in thyroid nodules too small to palpate it can guide the needle that will perform the biopsy;
  • Iodine scintigraphy – helps determine if a lump in the neck may be thyroid cancer. It is also used in people who have already been diagnosed with differentiated thyroid cancer (papillary, follicular, or Hürthle cell) to see if it has spread. For this test, a small amount of radioactive iodine is swallowed or injected into the vein – the iodine is taken up by the thyroid gland (or thyroid cells anywhere in the body) and a special camera is used to see where the radioactivity is because medullary thyroid cancer cells do not take up iodine;
  • Computed tomography (CT) scan of the neck and chest – multiple X-ray test that makes detailed cross-sectional images of the body. Help determine the location and size of thyroid cancer and see if it has spread to nearby areas or to distant organs, such as the lungs. One problem with CT in relation to thyroid cancer is that the contrast dye contains iodine, which interferes with radioiodine scans. For this reason, an MRI scan is often preferred for evaluation of the neck, or the CT scan is performed without contrast;
  • MRI of the neck – provides detailed images of the thyroid gland, the tumor, and any lymph nodes that are compromised by disease in the neck;
  • PET Scan – the positron emission tomography (PET Scan) can be very useful if the thyroid cancer is one that does not absorb radioactive iodine. In this situation, by PET scan it is possible to see if the cancer has spread.

The puncture/biopsy is fundamental to close the diagnosis of the disease. The simplest way to find out if a nodule is cancerous is by fine needle aspiration (FNA). This type of biopsy can often be done in the doctor’s office, with or without local anesthetic. Bleeding at the biopsy site is very rare, except in people with bleeding disorders.

Treatment

The treatment for thyroid cancer is usually surgical, and a total thyroidectomy (removal of the entire thyroid) or partial (only part of the thyroid), with the removal or not of the lymph nodes (swellings) of the neck, may be done, depending on each case.

In well-differentiated carcinomas, the surgical treatment can be complemented with radioactive iodine in order to reduce the risk of cancer recurring. Medullary carcinoma and anaplastic carcinoma do not respond to iodine, and this therapy is not used in these cases.

For cases of metastatic disease, other therapeutic options for disease control include tyrosine kinase inhibitors (oral medications).

Prevention

Several inherited diseases have been associated with different types of thyroid cancer, as has family history. However, most people who develop thyroid cancer do not have an inherited disease or a family history of the disease. The only possible prevention involves avoiding the risk factors (such as radiation exposure and iodine-poor diets mentioned earlier).

There is no scientific evidence that screening for thyroid cancer brings more benefits than risks and therefore at the moment it is not recommended.

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