Thyroid Cancer

Introduction

Thyroid lumps are a common presentation, seen in up to 5% of the population, however only a small proportion of them are cancerous.

There are different types of cancer that can affect the thyroid gland, all of which can present with different features. The main types of thyroid cancer are papillary, follicular, medullary, anaplastic, and lymphoma.

Fig. 1 – Anterior view of the neck, showing the anatomical position of the thyroid gland

Thyroid Cancer Subtypes

Papillary Carcinoma

This is the commonest type of thyroid cancer (75%), most commonly seen between 40-50 years and in women.

There can be multiple lesions within the gland and they are rarely encapsulated. Histologically, cells are a mixture of papillary and colloid-filled follicles, with papillary projections and pale empty nuclei. jThey commonly spread via the lymphatics.

Follicular Carcinoma

Usually seen at 40-60 years and in women, the second most common thyroid malignancy (15%).

They present as focal encapsulated lesions (multifocal disease is rare), with microscopic capsular invasion*. Where metastasis occurs, it is usually via haematogenous spread to bones and lungs.

*Hurthle cell tumours are a variant of follicular neoplasms in which oxyphil cells predominate

Medullary Carcinoma

These make up around 3% of thyroid cancers and arise in the parafollicular cells (C-cells, derived from the neural crest cells). Consequently, they produce a raised calcitonin levels and are associated (20% cases) with MEN II syndrome.

Medullary carcinoma can spread by both lymphatic and medullary routes; unfortunately nodal disease is associated with a very poor prognosis.

Anaplastic Thyroid Cancer

These rare tumours, accounting for 5% of thyroid cancers, usually present in the elderly and are very aggressive.

They tend to grow rapidly with early local invasion and often have spread by the time of presentation. Prognosis is poor and treatment is supportive.

Lymphoma

Thyroid lymphomas are very rare, making up only 1-2% of all thyroid cancers. They usually present in people over 60 years old.

They may grow quite rapidly, with marked compressive symptoms and B-Cell symptoms.

Fig. 2 – Histological slides of the thyroid cancer subtypes: (1) Papillary (2) Follicular (3) Medullary (4) Anaplastic


Risk Factors

  • Female
  • Family history
    • Also includes relevant cancer syndromes (e.g. medullary subtype associated with Multiple Endocrine Neoplasia (MEN) Syndrome type II)
  • Radiation exposure in childhood
  • Full body radiotherapy for bone marrow transplant
  • Hashimoto’s disease
    • Predisposes to lymphoma subtype

Clinical Features

Thyroid cancers maybe present as a palpable lump, multiple lumps, or be found incidentally on imaging of the neck.

The red flag signs to be aware of with any neck lump are:

  • Pain
  • Rapid growth
  • Cough, hoarse voice, or stridor
  • Multiple enlarged cervical lymph nodes
  • Tethering of the lump to surrounding structures

Differential Diagnosis

Fig. 3 – A Thyroid Neck Lump

It is important to remember that most lumps or swellings of the thyroid are not malignant, however some of them may still require surgical intervention for diagnosis or management.

  • Benign thyroid adenoma or thyroid cyst
  • Toxic multinodular goitre
    • Toxic refers to excessive productive of thyroid hormone which results in the clinical features of hyperthyroidism
  • Non-toxic multi-nodular goitre
  • Thyroglossal duct cyst (not in the thyroid itself)
    • Will move superiorly as the patient sticks out their tongue

Investigations

Most patients with a neck lumps should have initial Thyroid Function Tests* (TFTs) performed. Any evidence of a toxic nodule (low TSH or raised T3 or T4, or radio-nucleotide imaging showing a “hot” nodule), then no further investigation for malignancy will be required as overactive nodules are very rarely malignant.

*Serum calcitonin may be useful for the diagnosis and monitoring of treatment response in medullary carcinoma.

 

Most cases of suspected thyroid malignancy require US thyroid, used to assess the nodule and look for cervical lymphadenopathy. Suspicious features on ultrasound include:

  • Microcalcifications
  • Hypoechongenicity
  • Irregular margin

A score will be allocated (U1-U5). U1-U2 lesions have low risk of malignancy and will not require fine needle aspiration cytology (FNAC), U3-U5 lesions should undergo FNAC.

Fig. 4 – US Thyroid showing an Anaplastic Thyroid Malignancy

Fine Needle Aspiration Cytology (FNAC) involves passing a needle into the thyroid nodule and aspirating cells out of it. These cells will be reviewed and the relevant score allocated (Thy1-Thy5); the TNM staging system is used for thyroid cancers once diagnosis is confirmed:

  • Thy1 is inconclusive and requires a further sample
  • Thy2 is non-malignant
  • Thy3 is follicular lesion and requires diagnostic hemithyroidectomy for histology to determine between follicular adenoma (benign) or carcinoma
  • Thy4 is suspicious and requires diagnostic hemithyroidectomy
  • Thy5 is malignant and requires work up for appropriate treatment

Management

Thyroid cancer should be managed by a Multi-Disciplinary Team, including endocrinologists, histopathologists, radiologists, oncologists, and ENT surgeons, alongside of specialist nurses and speech and language therapists.

The management varies depending on the type of cancer as well as the stage. Management options include surgical, chemotherapy, radiotherapy, and radio-iodine therapy.

Surgical Treatment

  • Hemi-thyroidectomy– This involves removing half of the thyroid that contains the lesion, however is only suitable for certain tumours (e.g. small low grade non-metastatic malignancy)
  • Total Thyroidectomy– This involves removing the whole thyroid (including the isthmus). Patients will always need to take thyroid hormone replacement following this surgery
  • Neck dissection – To remove groups of lymph nodes in cases of locally advanced disease

Complications of Thyroid Surgery

Bleeding immediately after the operation can result in a haematoma forming beneath the skin. Large haematomas can cause airway obstruction, which is an emergency. In this situation the surgical wound must be re-opened (on the ward!) to allow drainage of the haematoma and the patient will need to go back to theatre to stop the bleeding.

Hypocalcaemia may occur if there is damage to or removal of the parathyroid glands. After a total thyroidectomy, patients must be monitored for symptoms of hypocalcaemia, such as paraesthesia or tetany.  PTH and serum calcium levels must be checked the next day (however levels can become significantly low within hours post-operatively)

The recurrent laryngeal nerves run close to the thyroid gland, hence care during surgery must to taken to prevent damage causing vocal cord paralysis. Unilateral  palsy will result in a hoarse voice however a bilateral paralysis can result in a life-threatening stridor and tracheostomy may be warranted.

Non-Surgical Treatment

Radioiodine therapy involves administration of a radioactive iodine solution, which is taken up preferentially by residual thyroid tissue, acting a focal radiation targeting the malignancy (used for papillary or follicular carcinomas). Only effective after total thyroidectomy.

External beam radiotherapy can be used as primary or adjunct therapy (curative or palliative). Chemotherapy can also be used for similar means, classically lymphomas usually responding well to chemotherapy, and symptoms can improve within a few doses.


Prognosis

The prognosis of thyroid cancer depends on the histological subtype, grade, and stage of the malignancy.

  • For papillary cancer, prognosis is quite good with 10 year survival of 90% (this drops considerably if the tumour has spread beyond the gland)
  • Follicular cancer has a high 10 year survival, at around 85% (haematogenous spread is a marker of poorer prognosis)
  • Medullary cancer also has a good prognosis, with 10 year survival dropping only below 90% when nodal or metastatic spread is seen.
  • Anaplastic thyroid cancer has a very poor prognosis with a 1 year survival of 10-20%

Quiz

Question 1 / 5
Which patient is most suspicious for thyroid cancer?

Quiz

Question 2 / 5
Which of the following types of thyroid cancer has the worst prognosis?

Quiz

Question 3 / 5
A patient is experiencing voice hoarseness several days post-operatively after thyroidectomy for follicular thyroid cancer. What is the most likely reason for this?

Quiz

Question 4 / 5
What blood test is used to test for recurrence of medullary thyroid cancer after initial treatment?

Quiz

Question 5 / 5
Which type of thyroid cancer has a hereditary component and is associated with MEN-2 syndrome?

Results

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