Thyroid cancer

Notes

Introduction

Thyroid cancer accounts for around 1% of new malignancies in the UK each year.

Thyroid cancer refers to a group of malignant conditions affecting the thyroid gland. They most commonly present with a thyroid lump and are diagnosed following triple assessment.

Surgical resection (thyroidectomy and hemithyroidectomy) is the mainstay of treatment. Prognosis is related to the type, stage and age at diagnosis.

This note will focus primarily on the diagnosis and management of papillary and follicular thyroid cancer (together often referred to as differentiated thyroid cancers).

Thyroid cancer statistics

Epidemiology

There are approximately 3,700 diagnoses of thyroid cancer in the UK each year.

It is more common in women who make up 70-75% of new diagnoses. Overall it is the 20th most common cancer in the UK.

Yearly figures show that over the past decades there has been a gradual increase in cases in both men and women.

Types

Papillary and follicular are the most common types of thyroid cancer.

We can broadly divide the types of thyroid cancer into:

  • Thyroid follicular epithelial derived cancer:
    • Papillary
    • Follicular
    • Anaplastic
  • Medullary thyroid cancer
  • Primary thyroid lymphoma

Comparison of types of thyroid cancer

Thyroid follicular epithelial derived cancer

Papillary is by far the most common thyroid cancer, accounting for around 70% of all thyroid cancers, whilst follicular accounts for 10-20%. Together, papillary and follicular cancers may be referred to as differentiated thyroid cancer.

Anaplastic cancer is far rarer accounting for around 2% of all thyroid tumours. They have a far graver prognosis developing rapidly with aggressive local spread. Median survival is just 3-8 months.

Medullary thyroid cancer

These are neuroendocrine tumours originating from parafollicular C cells. In 75% of cases they are sporadic but in the remaining 25% there is an association with MEN type 2 and mutation of the RET proto-oncogene.

Surgical resection forms the mainstay of management. In MEN type 2 where penetrance approaches 100%, prophylactic thyroidectomy is indicated.

Primary thyroid lymphoma

This is a rare condition accounting for approximately 2% of thyroid cancers. It typically occurs on a background of Hashimoto’s thyroiditis. Treatment tends to consist of radiotherapy, chemotherapy or a combination of the two.

Risk factors

There are a number of risk factors associated with papillary and follicular thyroid cancer.

The major risk factors are: 

  • Radiation exposure (particularly in childhood)
  • Family history / familial thyroid cancer
  • Female sex

Other risk factors include obesity, endemic goitre, FAP and Cowden’s syndrome

Clinical features

The most common presentation of differentiated thyroid cancer is a thyroid nodule/mass.

The majority (90-95%) of those with a thyroid lump will have benign disease, however further work-up is often needed. Clinical features that may be seen include:

  • Thyroid nodule / mass
  • Hoarseness / change in voice
  • Cervical lymphadenopathy
  • Stridor 

Referral

Any patient with suspected thyroid cancer should be referred on a two-week wait pathway.

Referral of thyroid lump

With reference to suspected thyroid cancer, NICE guidelines: Suspected cancer: recognition and referral (2015) advise:

  • Consider a suspected cancer pathway referral for thyroid cancer in people with an unexplained thyroid lump.

Remember - if there are signs of upper airway obstruction such as stridor arrange for urgent hospital admission and ENT review.

Evaluation

Suspicious thyroid lumps should be investigated with clinical examination, ultrasound scan +/- fine needle aspiration cytology (FNAC).

1. History, examination and thyroid function tests

All patients should have a full clinical review including a medical history (carefully evaluating family history and any exposure to radiation). This is followed by a clinical examination looking for signs of thyroid hormone imbalance and lymphadenopathy as well as evaluating the nodule itself. TFTs should be sent if not already by the referring clinician. 

2. Ultrasound scan

Ultrasound is the imaging modality of choice for thyroid lumps. A score U 1-5 is given based on the radiographical appearance of the nodule.

  • U 1: Normal
  • U 2: Benign
  • U 3: Indeterminate/equivocal 
  • U 4: Suspicious 
  • U 5: Malignant

In addition, any lymphadenopathy, retrosternal extension or tracheal compression should be commented upon. 

FNAC should be carried out on all U 3 – 5 lesions. Patients with U 1 and U 2 lesions do not need FNAC unless considered high risk for malignancy.

3. Fine needle aspiration cytology 

FNAC allows for cytological assessment of a thyroid nodule. Reports may classify results as:

  • Thy 1: Non-diagnostic
  • Thy 2: Non-neoplastic
  • Thy 3:
    • Thy 3a: Atypical features, may be suboptimal specimen, at times repeat FNAC indicated
    • Thy 3f: Follicular neoplasm suspected, cannot determine between hyperplastic nodule, follicular adenoma and follicular cancer
  • Thy 4: Likely malignancy (68-70%)
  • Thy 5: Malignancy (98-99%)

Pre-operative investigations

The triple assessment described above are the most important pre-operative investigations.

All patients will have an USS, TFTs and cytology result prior to any operative procedure. In those with extra-thyroidal extension or lymph node involvement additional imaging in the form of MRI or CT may be arranged. Suspicious lymph nodes may be sampled with FNAC.

Patient specific investigations may be organised depending on specific risk factors as part of routine pre-assessment (e.g. Echo). 

It is generally considered good practice to formally evaluate vocal cord function with Fiberoptic Nasendoscopy (FNE) pre-operatively.

Diagnostic surgery

Patients with Thy3f have cytology that cannot differentiate between follicular cancer and benign lesions may need a diagnostic hemithyroidectomy.

Those with Thy3f cytology generally need a diagnostic hemithyroidectomy (following case discussion at MDT). The tissue is sent for histology and if cancer is found a completion thyroidectomy may be completed following discussion with the patient and at MDT. Intra-operative frozen section is not used for follicular lesions.

Intra-operative frozen section may be completed on small, discrete lesions suspicious for papillary cancer with Thy4 cytology. This can allow single stage surgery.

Surgical management

Surgical resection forms the mainstay of management.

Surgery

Total thyroidectomy is commonly performed but increases the risk of hypoparathyroidism. Hemithyroidectomy may be considered in those with small, unifocal tumours without extra‐thyroidal spread.

Lymph node involvement requires appropriate lymph node dissection. Central and selective lateral neck dissection may be completed.

Post-op care

Serum calcium (+/- PTH) are monitored post-operatively. Normally that evening and the following morning at a minimum. Ongoing testing will depend on the levels.

It is generally considered good practice to formally evaluate vocal cord function with Fiberoptic Nasendoscopy (FNE).

Complications

Recurrent laryngeal nerve injury

Damage to the recurrent laryngeal nerve results in vocal cord dysfunction. This may present as a change in the character of a patients voice. Bilateral injury can threaten the airway and present with stridor - a medical emergency.

Recurrent laryngeal nerve anatomy

Haematoma

Rarely post-operative bleeding leads to the development of a haematoma in the neck. There is limited space for expansion and increasing pressure can threaten the airway.

An immediate medical emergency call should be put out and the surgical ward cover will re-open the neck on the ward if the airway is compromised. The patient will need to return to theatre for haemostatic control.

Hypoparathyroidism

Thyroidectomy risks the removal, de-vascularisation or damage of the parathyroid glands, responsible for calcium homeostasis.

Around 30% of patients will need calcium (+/- alfacalcidol) supplementation after a total thyroidectomy. This hypoparathyroidism is normally transient with less than 10% affected at 3 months.

Complications of thyroidectomy

Adjuvant therapy

Adjuvant therapy may be used to increase the chance of cure or long term remission.

Radioiodine remnant ablation

131Iodine mediated destruction of remnant thyroid tissue may be used as an adjunct to total or near total thyroidectomy. The decision to use RRA is taken by MDT with reference to the patients wishes.

External beam radiotherapy

EBRT may be considered in certain patients with high risk features (high risk of recurrence, local spread, residual/recurrent tumour).

In may also be used in the palliative setting, particularly in cases of bone/spinal and brain metastasis.

Further management

TSH suppression and thyroglobulin monitoring may be used to aid managment.

TSH suppression

Suppression of TSH with supra-normal levels of levothyroxine can reduce the risk of recurrence. This treatment is not without risks that include osteoporosis, AF and cardiovascular disease.

The decision to offer suppression is made by specialist MDT taking into account a myriad of factors.

Thyroglobulin

Thyroglobulin is a large glycoprotein produced by both normal and cancerous thyroid cells. It can be used post-operatively to assess for residual tissue or recurrent disease. It is normally first measured 6 weeks after surgery.

In patients who have not had total thyroidectomy and radioiodine remnant ablation it can be difficult to differentiate between residual tissue, residual disease or recurrent disease. Serial measurement and trends can be helpful.

Prognosis

As with most malignancies prognosis is related to stage and age at diagnosis. 

According to figures from Cancer Research UK overall:

  • 91.4% survive one year or more
  • 87.4 survive five years or more

Prognosis is better for younger and female patients, almost everyone diagnosed aged 15-49 survive their disease for five years or more.

Pulsenotes uses cookies. By continuing to browse and use this application, you are agreeing to our use of cookies. Find out more here.