Box 3.31Classification of thyroid epithelial cell tumors

These are classified according to histological features

Primary

• Adenomata
  • Follicular — including colloid, Hurthle cell and other variants
  • Papillary — this may include some follicular elements
  • Teratoma
• Carcinomata
  • Differentiated
    • Papillary
      • Pure papillary
      • Mixed papillary and follicular
      • Follicular
  • Undifferentiated
• Other — e.g. lymphoma, fibrosarcoma

Secondary

• TNM Grading
• T — primary tumor
  • T0 — no palpable tumor
  • T1 — single tumor confined to the gland
  • T2 — multiple tumors confined to the gland
  • T3 — tumor extending beyond the gland
• N — regional lymph nodes
  • N0 — no palpable nodes
  • N1 — moveable nodes on one side
  • N2 — moveable bilateral nodes
  • N3 — fixed nodes
• M — distant metastases
  • M0 — none
  • M1 — distant metastases

Clinically, the dominant factor in governing prognosis in thyroid epithelial cell cancer is age. Others factors include size of primary tumor, degree of invasiveness, histological grade and the presence of metastases. Of these, all except histological grade are incorporated into the TNM classification.