Tumour of the parafollicular cells which secrete calcitonin (C-cells)

Aetiology

• Can be:
  • Sporadic (70%) - seen in adults (40s-50s)
  • Medullary carcinoma associated with Multiple Endocrine Neoplasia Type 2a (MEN2a) can arise in very young patients
    • MTC associated with phaeochromocytoma and hyperparathyroidism in these patients
    • Consider prophylactic thyroidectomy as child
  • Familial non-MEN seen in adults (40s-50s)

Genetic features

• Germline RET mutations

Pathophysiology

Morphology

• Sporadic cases - solitary nodule
• Familial cases - bilateral/multicentric
  • C cell hyperplasia
• Composed of spindle or polygonal cells arranged in nests, trabeculae or follicles
• Associated amyloid deposition (abnormally folded calcitonin)

Prognostic factors

Good prognostic factors

• Young age, female
• Smaller tumour rise, confined to thyroid, no metastases

Negative prognostic factors

• Necrosis
• Many mitosis
• Squamous metaplasia
• Small cell morphology