Thyroid Nodules & Cancer — UKMLA Guide 2026

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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.

Key points

Thyroid nodules are very common (~50% by USS in >50 year olds) — the vast majority are benign
Red flags for malignancy: rapid growth, fixation, hoarse voice, cervical lymphadenopathy, family history (MEN2)
Investigation: TSH → if normal/elevated: USS with U-classification → FNAC if U3–U5 → Thy cytology grading
Papillary carcinoma is the commonest (80%) — excellent prognosis. Follicular (10–15%). Medullary (5%) — check calcitonin. Anaplastic (<2%) — very poor prognosis
Treatment: total thyroidectomy ± radioactive iodine ablation ± TSH suppression with levothyroxine
Suspected cancer pathway referral for unexplained thyroid lump (NICE NG12)

Overview

Thyroid nodules are discrete lesions within the thyroid gland that are distinct from the surrounding parenchyma. They are extremely common — palpable in approximately 5% of adults and detectable by ultrasound in up to 50% of those over 50. The vast majority are benign (colloid nodules, cysts, follicular adenomas). Thyroid cancer accounts for approximately 3,800 new cases per year in the UK. The main histological types are: papillary (80%), follicular (10–15%), medullary (5% — from parafollicular C-cells, associated with MEN2), and anaplastic (<2% — undifferentiated, very aggressive). Differentiated thyroid cancers (papillary and follicular) have an excellent prognosis with 10-year survival >95%.

Epidemiology

Thyroid cancer is the most common endocrine malignancy. Incidence is rising, partly due to incidental detection on imaging. Female:male ratio approximately 3:1. Peak incidence 30–50 years for papillary and follicular types. Risk factors include: previous neck irradiation (especially in childhood), family history (MEN2 for medullary, familial adenomatous polyposis for papillary), iodine deficiency (increases follicular type risk), and female sex. Medullary thyroid cancer is associated with MEN2A (medullary thyroid cancer + phaeochromocytoma + hyperparathyroidism) and MEN2B (medullary + phaeochromocytoma + mucosal neuromas + Marfanoid habitus) via RET proto-oncogene mutations.

Clinical Features

Symptoms

Painless thyroid lump or swelling — most common presentation

Often incidental finding on examination or imaging

Hoarseness (recurrent laryngeal nerve involvement)

Dysphagia or sensation of pressure in the neck

Stridor (tracheal compression — advanced disease)

Rapid enlargement of a thyroid lump

Signs

Firm, irregular, non-tender thyroid nodule

Fixed nodule (does not move with swallowing)

Cervical lymphadenopathy

Vocal cord paralysis on flexible nasendoscopy

Most patients are euthyroid — TFTs usually normal unless concurrent thyroid disease

Investigations

First-line

TSHFirst-line. If suppressed → suggests autonomous nodule (hot nodule) → technetium scan. Hot nodules are rarely malignant

Thyroid ultrasound (USS)Characterise nodule using U-classification (U1=normal, U2=benign, U3=indeterminate/equivocal, U4=suspicious, U5=malignant)

Second-line

Fine needle aspiration cytology (FNAC)USS-guided FNAC for U3, U4, U5 nodules. Thy classification: Thy1=non-diagnostic, Thy2=non-neoplastic, Thy3=neoplasm possible/suspected, Thy4=suspicious of malignancy, Thy5=malignant

CalcitoninMeasure if medullary thyroid cancer suspected (family history of MEN2, suspicious USS features). Elevated in MTC. NOT routine for all nodules (NICE NG230)

Specialist

CT neck and chestStaging — assess for local invasion and pulmonary metastases

Genetic testing (RET mutation)If medullary thyroid cancer confirmed — screen for MEN2. Cascade testing of first-degree relatives

ThyroglobulinTumour marker for differentiated thyroid cancer — used post-operatively for surveillance, not for initial diagnosis

Management

NICE NG230 (Thyroid cancer), 2022; NICE NG12 (Suspected cancer), 2015

Referral

Suspected cancer pathway referral for anyone with an unexplained thyroid lump (NICE NG12)
Benign nodules (U2, Thy2): discharge or monitor depending on size and symptoms
Indeterminate (U3, Thy3): diagnostic hemithyroidectomy or active surveillance depending on clinical context

Surgery

Total thyroidectomy: for most thyroid cancers, especially if bilateral, >4 cm, extrathyroidal extension, or nodal metastases
Hemithyroidectomy (lobectomy): may be sufficient for low-risk papillary microcarcinoma (<1 cm) or minimally invasive follicular cancer
Central ± lateral neck dissection if lymph node metastases
Risks: recurrent laryngeal nerve injury (hoarseness), hypoparathyroidism (hypocalcaemia), bleeding/haematoma

Radioactive iodine (RAI) ablation

Post-thyroidectomy for differentiated thyroid cancer — destroys residual thyroid tissue and micrometastases
Requires thyroid hormone withdrawal (or recombinant TSH) to raise TSH before administration
Not effective for medullary or anaplastic types (do not take up iodine)

Thyroid hormone suppression + surveillance

Levothyroxine at TSH-suppressive doses (target TSH <0.1 mU/L) for differentiated thyroid cancer — reduces recurrence
Surveillance: thyroglobulin levels + neck USS. Rising thyroglobulin suggests recurrence
Medullary thyroid cancer: follow calcitonin and CEA levels

Complications

Surgical complications: Recurrent laryngeal nerve palsy (hoarseness), hypoparathyroidism (hypocalcaemia — may be permanent), haematoma
Hypothyroidism: Inevitable after total thyroidectomy — lifelong levothyroxine
Recurrence: ~10–15% for papillary/follicular. Detected by rising thyroglobulin or structural disease on imaging
Metastases: Papillary → cervical lymph nodes (common, good prognosis). Follicular → haematogenous (lung, bone). Anaplastic → rapidly locally invasive
MEN2-associated cancers: If medullary thyroid cancer → screen for phaeochromocytoma (before thyroid surgery to avoid crisis)

UKMLA Exam Tips

1Papillary = most common, lymph node spread, psammoma bodies on histology, excellent prognosis. "Papillary Pushes to nodes"
2Follicular = haematogenous spread (lung/bone), cannot distinguish from adenoma on FNAC (need capsular invasion on histology)
3Medullary = C-cells, produces calcitonin, associated with MEN2. Always check for phaeochromocytoma BEFORE surgery
4Anaplastic = undifferentiated, elderly, rapidly enlarging hard mass, very poor prognosis (<6 months)
5Cold nodule on isotope scan = not functioning = higher malignancy risk. Hot nodule = functioning = rarely malignant
6Unexplained thyroid lump → suspected cancer pathway referral (NICE NG12). Do NOT delay for TFTs
7Post-thyroidectomy hypocalcaemia: check calcium within 24 hours. Chvostek and Trousseau signs = hypocalcaemia

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