Over the last several decades, the prevalence of thyroid cancer has risen sharply in many high-income countries, including Canada. An estimated 6300 Canadians are diagnosed with thyroid cancer annually, and it is the sixth most common cancer among women.

TYPES OF THYROID CANCER

There are 4 different types of thyroid cancer: papillary, follicular, medullary, and anaplastic. Papillary thyroid cancer (PTC) is the most common type, and accounts for nearly 80% of cases. Follicular thyroid cancer (FTC) accounts for 5-10% of cases. Taken together, papillary and follicular thyroid cancer represent “differentiated thyroid cancer” (DTC) which carries an excellent prognosis for most patients. Medullary thyroid cancer (MTC) occurs in 5% of cases, arising from a type of cell within the thyroid called parafollicular cells. Around 25% of MTC present as part of a hereditary syndrome. Anaplastic thyroid cancer (ATC) is a rare form of thyroid cancer accounting for only 1-2% cases, and carries a very poor prognosis. Occasionally, individuals develop lymphoma of the thyroid gland or have other types of cancer that spread to the thyroid.

DIAGNOSIS

The diagnosis of thyroid cancer is made on the basis of a fine needle aspiration (FNA) biopsy of a thyroid nodule and/or a suspicious lymph node. The biopsy result usually specifies what type of thyroid cancer it is (PTC, MTC, or ATC) but FTC are more difficult to diagnose on a biopsy.

Occasionally, the biopsy comes back “indeterminate” meaning the pathologist cannot tell if the nodule is benign or cancerous based on the biopsy sample. In select cases, patients undergo surgical removal of the thyroid lobe that contains the nodule in question, termed a “diagnostic lobectomy” to arrive at a diagnosis. If cancer is found on the diagnostic lobectomy, a subset of patients will need a second surgery (“completion thyroidectomy”) to take out the other lobe to facilitate follow up and radioactive iodine.

MANAGEMENT

The management of thyroid cancer depends on the type, size, and stage of the thyroid cancer. Although in the past the mainstay of treatment for DTC was total thyroidectomy (complete surgical removal of the thyroid) followed by radioactive iodine, modern treatment is tailored to the individual and the aggressiveness of their cancer.

Broadly speaking, there are 3 possible approaches to the initial management of thyroid cancer:

1. Active surveillance of low risk papillary microcarcinoma: monitoring the thyroid cancer with neck ultrasound (also known as “watchful waiting”) as opposed to immediate surgery
   • There is increasing evidence for the safety of active surveillance as opposed to immediate surgery for small (typically < 1-2 cm), low risk PTC that are confined to the thyroid.
   • Safe monitoring of thyroid cancers requires ongoing medical follow up, access to high quality neck ultrasounds, and an experienced medical team comprising of a radiologist and clinician (endocrinologist or thyroid surgeon).
   • The obvious benefit of active surveillance is avoiding surgery and being able to keep one’s thyroid, however, this approach is not right for everyone, and interested patients should discuss their eligibility with their healthcare team.
2. Lobectomy: surgical removal of half the thyroid
   • Patients with tumors between 1-4 cm, confined to the thyroid, and with no concerning nodules in the other lobe of the thyroid, may be eligible for a lobectomy for treatment of their thyroid cancer.
3. Total thyroidectomy: surgical removal of the entire thyroid
   • This remains the most common treatment approach for thyroid cancers and is necessary is cases where it is expected that the patient will require radioactive iodine post-operatively
   • Total thyroidectomy is undertaken due to larger tumour sizes, when there is suspicion that the thyroid cancer has spread outside the thyroid to lymph nodes or surrounding neck structures, or for any other reason where it is expected that the patient will need radioactive iodine.

Thyroid surgeons will discuss eligibility for lobectomy versus total thyroidectomy, including surgical risks, complications, and the pros/cons of each approach. Patient preference is also an important consideration for deciding on the extent of surgery.

POSTOPERATIVE MANAGEMENT

Your medical team will integrate details about your thyroid cancer including the preoperative imaging (usually neck ultrasound), operative report, pathology report, and post operative tests such as thyroid tumour marker (“thyroglobulin”) to arrive at the AJCC stage and ATA risk of recurrence of a cancer.

It is very important that your medical team have access to your pathology report. The most important pathology features about a thyroid cancer include the tumour size, whether the tumour spread outside the thyroid or not (“extrathyroidal extension”), the size and number of metastatic lymph nodes found, and whether cancer cells were found inside the blood vessels of the thyroid (“vascular invasion”).

RADIOACTIVE IODINE THERAPY

Depending on the findings at the time of surgery, radioactive iodine may be considered post-operatively. Radioactive iodine is administered in either a capsule or liquid form several weeks after surgery. Most patients are prepared for the radioactive iodine with a low iodine diet (lasting between 5-14 days depending on the centre), as well as a drug called recombinant TSH (Thyrogen®). After the radioactive iodine is administered, patients need to follow certain protocols/procedures to ensure they do not expose others to radiation. Occasionally, patients require admission to hospital for a few days where they carry out their isolation.

Immediate side effects of radioactive iodine include nausea, headache, and transient neck discomfort. These symptoms typically last for a few hours to a few days and are easily treated with supportive medication such as pain killers or anti-nausea medication. Symptoms that can last for a few weeks to a few months include decreased saliva and tear formation (resulting in dry mouth and eyes) and alteration in taste. Most patients will only require one dose of radioactive iodine, however, occasionally this treatment is repeated if residual or recurrent thyroid cancer is detected. Data suggests a slight increase in secondary cancers in patients receiving high doses of radioiodine over their lifetime.

EXTERNAL BEAM RADIATION THERAPY (EBRT)

In certain aggressive cases of thyroid cancer, patients require external beam radiation therapy after or instead of thyroid surgery. External radiation is administered over a 4 to 6 week interval in small divided doses to the neck region. A radiation oncologist will be involved in cases where EBRT is being considered and will discuss the treatment details including expected side effects such as sore throat or skin reactions.

CHEMOTHERAPY

Traditional chemotherapy is not very effective against thyroid cancer and is thus seldom used. However, metastatic thyroid cancer that is growing and not responding to radioactive iodine (known as “radioactive iodine refractory thyroid cancer”) can be treated by a class of medication known as tyrosine kinase inhibitors (TKI). TKI are oral pills taken daily and work by disrupting the blood supply to tumour cells. TKI therapy has a number of known and expected side effects and treatment with TKI should only be undertaken by an experienced multidisciplinary team, typically when other treatment options such as surgery or RAI have been exhausted.

POST TREATMENT CHECK-UPS

Long term follow up of thyroid cancer entails the following:

1. Thyroid hormone replacement therapy: your doctor will keep an eye on your thyroid hormone levels through measurement of TSH (and occasionally thyroid hormone levels). The target TSH level depends on the stage/risk of the thyroid cancer, the status of the disease (in remission or recurring), and the patient’s other medical problems and symptoms related to hypothyroidism or hyperthyroidism.
2. Surveillance: your doctor will monitor you for thyroid cancer recurrence through measurement of serum thyroglobulin (Tg) which is a tumour marker for thyroid cancer that is detected in the blood. In addition, patients will need neck ultrasounds, and occasionally other imaging like CT scan or PET scan. The frequency and type of medical imaging depends on the stage/risk of the thyroid cancer and the status of the cancer. In general, lower risk cancers need less frequent imaging, and higher risk cancers need more frequent imaging.

Your doctor will integrate your tumour marker level (Tg) and imaging results to communicate about the status of your thyroid cancer (whether it is all gone or if there is evidence that it is growing back).

 

Updated in May 2024 by Sana Ghaznavi, MD, FRCPC, Clinical Assistant Professor, Division of Endocrinology & Metabolism, at the University of Calgary, from the original text written by: Irving B. Rosen, MD., FRCS(C), FACS, and Paul G. Walfish CM, MD, FRCP(C), FACP, FRSM.