6. Thyroid malignancies: staging and treatment

Thyroid malignancies: staging and treatment

OVERVIEW AND HISTOLOGY

• Thyroid cancer includes differentiated papillary and follicular carcinoma, medullary carcinoma from parafollicular C cells, and anaplastic carcinoma.
• Papillary carcinoma is the commonest and often spreads via lymphatics to cervical nodes.
• Follicular carcinoma more often spreads haematogenously to bone and lung; capsular or vascular invasion distinguishes carcinoma from follicular adenoma.
• Medullary carcinoma may be sporadic or associated with MEN2/RET mutations and secretes calcitonin.
• Anaplastic carcinoma is aggressive, often presents in older adults with a rapidly enlarging neck mass and compressive symptoms.

RISK FACTORS AND ANATOMY

• Risk factors include childhood head/neck radiation, familial syndromes, family history and certain genetic alterations.
• The thyroid is adjacent to the trachea, oesophagus, recurrent laryngeal nerves and parathyroids; tumour invasion or surgery may affect voice, swallowing and calcium regulation.
• Cervical nodal levels and central compartment nodes are important for staging and operative planning.

CLINICAL PRESENTATION

• A thyroid nodule is often asymptomatic.
• Suspicious features include rapid growth, hard/fixed nodule, vocal cord palsy, cervical lymphadenopathy, prior radiation or strong family history.
• Papillary cancer may present with a lateral neck node.
• Medullary cancer may be associated with diarrhoea/flushing in advanced disease or endocrine features of MEN2.
• Anaplastic cancer can cause dysphagia, dyspnoea, stridor and pain.

DIAGNOSIS AND STAGING

• Initial evaluation includes TSH and high-resolution ultrasound of thyroid and cervical nodes.
• Ultrasound features of concern include marked hypoechogenicity, irregular margins, microcalcifications, taller-than-wide shape and suspicious nodes.
• Fine-needle aspiration is interpreted using a standard cytology system; indeterminate follicular-pattern lesions may require diagnostic lobectomy because cytology cannot assess capsular/vascular invasion.
• Measure calcitonin when medullary carcinoma is suspected or according to local practice.
• For medullary cancer, assess RET and screen for pheochromocytoma and hyperparathyroidism before thyroid surgery.
• CT/MRI is used for bulky, invasive or substernal disease; laryngoscopy documents vocal cord function when indicated.

STAGING

• AJCC TNM staging uses tumour size and local extension (T), regional lymph nodes (N) and distant metastases (M).
• Age is incorporated into differentiated thyroid cancer staging and the age cut-off differs by staging edition; use the current local AJCC edition rather than memorising outdated cut-offs.
• Risk stratification after surgery also considers histology, extent, margins, vascular invasion, nodal burden, postoperative thyroglobulin and imaging.
• Staging predicts disease-specific mortality, while recurrence-risk systems guide follow-up intensity.