Thyroid carcinoma is the commonest endocrine malignancy and accounts for about 0.5% of newly diagnosed cancer. About 4-7% of the population will have a clinically evident thyroid nodule (which is 4 times commoner in women) and about 2-3% of these are malignant.

Risk factors for thyroid malignancy

• MEN II
• Radiation exposure
• A prior thyroid malignancy
• Age (children and the over 60s more at risk)
• Evidence of effect on surrounding structures (hoarseness, stridor or dysphagia)
• Presence of lymphadenopathy
• Patients with a family history of polyposis syndromes
• A single cold nodule

Presentation

Most present with an asymptomatic neck mass. About a 1 in 5 will have palpable lymphadenopath.

Differential Diagnosis

1. Adenoma
2. Cyst
3. Goitre
4. Nodular hyperplasia
5. Carcinoma
6. Lymphoma
7. Metastasis

Follicular adenoma

Forms the majority of benign disease but remember this is on full histology only. FNAC can not differentiate between follicular adenoma and carcinoma and so surgical excision is required. Most consider it reasonable to perform lobeectomy and await histology. See follicular carcinoma below for the controversy in treatment.

• Can be inactive but most are
• Isotope scanning might show up a cold nodule (10%)

Papillary Adenoma

There is no such thing as a papillary adenoma, all should be considered malignant and treated as such.

Papillary carcinoma

• Makes up about 70% of the thyroid cancers
• Occurs in a young popluation, 20-40 years old
• More common in females (3:1)
• Tend to be multiple and un-encapsulated
• Spread is via lymphatics and cervical node involvement occurs early in the disease. Distant metastasis are rare.
• Note the "lateral aberrant thyroid" is a mis-nomer and usually represents cervical metastasis from this tumour
• Tumours can be mixed papillary / follicular. Should be treated as papillary even if mainly follicular
• Can be diagnosed on FNAC

Treatment can be by thyroid lobectomy if the tumour is confined in a single lobe otherwise a total thyroidectomy is required. Local lymph node spread can be treated with a modified cervical block disection and radio-active iodine is only required if the tumour has invaded beyond the capsule.

Thyroxine should be given after a lobectomy to suppress disease recurrance and of would be needed after total thyroidectomy.

Follicular carcinoma

• Forrms about 15% of the tyroid malignancies
• Usually an older age group than papillary (mean age 45)
• More common in females (3:1)
• More common in regions with endemic goitres
• Usually solitary and encapulated
• Heamatogenous spread to lung and bone
• Local lymph node spread is a sign of late disease

The reason FNAC can not be used to differentiate is that malignancy is defined as capsular invasion and vascular spread and is not based on cytology.

The treatment is controversial. Classical teaching is to perform a total thyroidectomy followed by radioactive iodine therapy. However, 80% of specimens removed will be benign and the risks of surgery are increased by performed a total thyroidectomy. Risk of permanent hypo-parathyroidism increases from 4% to 9% and the risk of recurrent laryngeal nerve injury from 1% to 9%.

A group of low risk individuals can be identified.

• Young (under 45)
• Tumour less than 4cm
• No Hurtle or T-cell variant on histology
• No extension beyond the thyroid gland
• No distant metastasis
• No lymph node involvement

For these low risk individuals a limited (i.e. hemi-thyroidectomy) seems reasonable. All patients should receive thyroxine afterwards to reduce thyroid stimulating hormone levels which seems to improve survival.

Medullary carcinoma

• Accounts for 5-10% of thyroid malignancy
• Arises in the para-follicular (C-cells) of the thyroid. These cells produce calcitonin
• Occurs in all age groups
• About one fifth are hereditary (note MEN II a or b) but most occur spontaneously
• Lymph node involvment is high at about 25% at presentation

These tumours can present with diarrohea due to hormone secretion (Calcitonin / carcinoembryonic antigen (CEA))

Treatment is by total thyroidectomy with a block disection on the side of the disease regardless of node status. If the disease is present in both lobes then bilateral block disection is required. Calcitonin levels can be used to monitor for recurrance. The use of radio-iodine, radio-therapy and chemo-therapy is reserved for recurrance. Node positive disease has a significantly worse 5 year survival at 50% cf 90% for node negative.

Lymphoma

• Rare (~1%)
• Remeber that this can represent secondary disease as well as de nova neoplasia
• Usually quite diffuse
• Occurs in the elderly and affects women more than men
• Rapid growth
• In about one third pre-existing Hashimoto's disease is found

For primary disease the treatment is total thyroidectomy with post-operative radiotherapy. If the diisease is secondaries or a recurrance then the treatment is with chemotherapy.

Squamous

• Very rare
• Should be distinguished from squamous metaplasia of a papillary tumour
• This is a very aggressive tumour and treatments are generally ineffective

Thyroid Sarcoma

• Again very rare and with a very poor prognosis

Thyroid Teratoma

• In adults a very aggressive malignancy with very few patients surviving 1 year
• In children however the disease is considered benign with most doing well after surgical excision

Metastatic Disease to the Thyroid

• Is rare
• When is does occur think breast, malignant melanoma or lymphoma

Further Reading

Risk group-based management of differentiated thyroid carcinoma : This RCS of Endinburgh article has a nice summary of the managment of follicular adenoma / carcinoma