Thyroid Cancer

Thyroid cancer is a malignancy originating from the tissues of the thyroid gland, characterised by abnormal cell growth with potential metastasis. It is commonly diagnosed through the presence of a neck swelling or lump and affects women more frequently than men.

Signs and Symptoms

The initial symptom of thyroid cancer is often a noticeable nodule in the thyroid region of the neck. While many adults have small thyroid nodules, less than 10% are cancerous. In some cases, an enlarged lymph node may be the first sign. Advanced symptoms include neck pain and voice changes due to recurrent laryngeal nerve involvement. Thyroid cancer is typically found in euthyroid patients, although hyperthyroidism or hypothyroidism may be present in large or metastatic tumours.

Causes and Risk Factors

The aetiology of thyroid cancer involves a combination of environmental and genetic factors. Ionising radiation exposure, especially in childhood, is a significant environmental risk. This includes radiation from medical treatments and nuclear accidents. Thyroiditis and other thyroid diseases also predispose individuals to thyroid cancer. Genetically, multiple endocrine neoplasia type 2 is a notable risk factor, particularly for medullary thyroid cancer.

Diagnosis

Diagnosis begins with the detection of thyroid nodules via physical examination, followed by an ultrasound to confirm the nodule and assess the thyroid gland. Blood tests measuring thyroid hormones and antibodies help identify associated thyroid diseases. A fine needle aspiration cytology test, reported according to the Bethesda system, is essential for a definitive diagnosis. For metastasis assessment or post-surgical monitoring, radioactive iodine scans may be employed. Routine screening for asymptomatic adults is not recommended.

Classification

Thyroid cancers are classified histopathologically into several types:

• Papillary thyroid cancer (75-85%): Common in young females with an excellent prognosis.
• Follicular thyroid cancer (10-20%): May include Hürthle cell carcinoma.
• Medullary thyroid cancer (5-8%): Associated with parafollicular cells and multiple endocrine neoplasia type 2.
• Anaplastic thyroid cancer (1-2%): Highly aggressive with poor treatment response.
• Other types: Including thyroid lymphoma, squamous cell thyroid carcinoma, and sarcoma of the thyroid.

Staging

Thyroid cancer staging uses the TNM system to determine the extent of cancer development. Various stages from T1a (small localised tumour) to T4b (advanced local invasion) are identified, guiding treatment options and prognosis.

Treatment

Initial treatment often involves thyroidectomy and possibly central neck dissection. Radioactive iodine-131 is used for ablation of residual tissue in well-differentiated cancers. External radiation may be applied for unresectable or recurrent cancers. Medullary and anaplastic thyroid cancers do not benefit from radioactive iodine therapy. Advanced metastatic cases may be treated with targeted therapies such as sorafenib and lenvatinib. Monitoring post-surgery includes imaging and blood tests for tumour markers.

Prognosis

The prognosis for thyroid cancer varies with type and stage. Papillary thyroid cancer has an excellent overall prognosis, with a 5-year survival rate of around 96-97%. The prognosis is generally better for younger patients and those diagnosed early. However, anaplastic thyroid cancer has a significantly poorer prognosis, with a 5-year survival rate of only 7-14%. Recent advancements in targeted therapies are improving outcomes for advanced stages.

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Self-assessment MCQs (single best answer)

What is the first noticeable symptom often associated with thyroid cancer?

Which type of thyroid cancer is most common?

What environmental factor is a significant risk for developing thyroid cancer?

Which genetic condition is particularly associated with medullary thyroid cancer?

Which diagnostic test is essential for definitively diagnosing thyroid cancer?

What is the typical prognosis for patients with papillary thyroid cancer?

Which treatment is NOT typically used for medullary thyroid cancer?

What does the TNM system in thyroid cancer staging refer to?

Which thyroid cancer type is highly aggressive with poor treatment response?

What is a common site for metastasis in thyroid cancer that can be detected in post-surgical monitoring?