Thyroid

What is thyroid cancer

The thyroid gland is located in 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 occurs when thyroid cells begin to grow and multiply uncontrollably.

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

The main risk factors for thyroid cancer are:

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

It’s worth noting that the presence of nodules in the thyroid 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 can appear at any age, but they are more common in older adults.

Subtypes of thyroid cancer

Different types of cancer develop from each type of cell in the region, which is important to detect because it impacts the severity of the cancer and the necessary treatment.

The main subtypes of thyroid cancer are:

• Well-differentiated carcinomas – their cells closely resemble normal thyroid tissue when viewed under a microscope. They develop from the follicular cells of the thyroid and account for the majority of thyroid cancers. Generally, they have a less aggressive behavior and are highly responsive to iodine therapy. Well-differentiated carcinomas, in turn, include three different subtypes: papillary (most common – 80% of cases), follicular, and Hurthle cell carcinoma;
• Medullary carcinoma – develops from the C cells of the thyroid gland, which normally produce calcitonin, a hormone that helps control the amount of calcium in the blood. It is rare and has a slow growth rate and no responsiveness to iodine therapy;
• Anaplastic carcinoma or undifferentiated carcinoma – is a rare form of thyroid tumor, accounting for about 2% of all cases. It is called undifferentiated because the cancer cells do not resemble 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

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

• Nodule or lump (especially if they grow rapidly);
• Swelling in the neck;
• Pain in the front of the neck, sometimes radiating to the ears;
• Hoarseness or other persistent voice changes;
• Difficulty swallowing;
• Breathing problems;
• Constant cough.

There are benign conditions that can 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 medical history of patients are the first steps in detecting thyroid cancer.

After 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 cancerous and determine if the neoplasm has spread, which impacts treatment choice. The main ones are:

• Ultrasound – is one of the first exams and helps determine if a thyroid nodule is solid or cystic (filled with fluid) – 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. Additionally, in nodules of the thyroid too small to be palpated, it can guide the needle that will perform the biopsy.
• Iodine Scan – 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 a 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, as medullary thyroid cancer cells do not take up iodine.
• Computed Tomography (CT) of the neck and chest – a test that uses multiple X-ray beams to create detailed cross-sectional images of the body. It helps determine the location and size of thyroid cancer and check if it has spread to nearby areas or distant organs, such as the lungs. One issue with CT scans for thyroid cancer is that the contrast dye contains iodine, which interferes with radioiodine scans. For this reason, an MRI scan of the neck may be preferred for evaluation, or the CT scan is performed without contrast.
• Magnetic Resonance Imaging (MRI) of the neck – provides detailed images of the thyroid gland, the tumor, and any lymph nodes that may be affected by the disease in the neck.
• Positron Emission Tomography (PET Scan) – PET scan can be very useful if the thyroid cancer is one that does not absorb radioactive iodine. In this situation, PET scan can determine if the cancer has spread.

Biopsy is fundamental to confirm the diagnosis of the disease. The simplest way to determine if a nodule is cancerous is through fine-needle aspiration (FNA) biopsy. This type of biopsy can often be done in the office, with or without local anesthesia. Bleeding at the biopsy site is very rare, except in people with bleeding disorders.

Treatment for thyroid cancer

The treatment for thyroid cancer is generally surgical, and it can involve either total thyroidectomy (complete removal of the thyroid) or partial thyroidectomy (removal of part of the thyroid), with or without the removal of lymph nodes in the neck, depending on each case.

In well-differentiated carcinomas, surgical treatment can be complemented with radioactive iodine to reduce the risk of cancer recurrence. Medullary and anaplastic carcinomas do not respond to iodine, so 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 of thyroid cancer

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

There is no scientific evidence that thyroid cancer screening brings more benefits than risks, and therefore, it is not recommended at this time.