WHO classification of thyroid tumours (1988)

I. Epithelial tumours

• Benign
  • Follicular adenoma and variants
  • Others including hyalinizing trabecular adenoma
• Malignant
  • Follicular carcinoma including minimally invasive, widely invasive and poorly differentiated subtypes
  • Papillary carcinoma and variants including papillary microcarcinoma, follicular variant and diffuse sclerosing variant
  • Medullary carcinoma and variants including mixed medullary-follicular carcinoma
  • Undifferentiated (anaplastic) carcinoma
  • Others

II. Non-epithelial tumours

• Benign
• Malignant
• Angiosarcoma
• Others

III. Malignant lymphomas

IV. Miscellanous tumours