Differentiated thyroid cancer (staging)

Successful treatment of thyroid cancer highly depends on accurate preoperative staging.

Ultrasound and ultrasound-guided FNA or core biopsy remain the investigation of choice for diagnosing primary thyroid malignancies. CT and MRI are inferior to ultrasound for characterising thyroid nodules, however, are useful for demonstrating extrathyroid extension and nodal metastases ⁴. 

It is important to note that patients who are to undergo diagnostic or therapeutic procedures involving radioisotope scanning of the thyroid (including thyroid cancer treatment) will have radioisotope uptake prevented for 8 weeks following iodinated contrast administration ³, and as such the risks and benefits of administering IV contrast should be considered and discussed with the referring clinician. 

Staging

For staging of the differentiated thyroid cancers (including papillary, follicular and medullary) the TNM staging system is widely used.

For anaplastic cancer, there is no generally accepted stating system and all patients with anaplastic thyroid cancer, all patients are considered to have stage IV disease.

T: Tumour

• Tx: primary tumour cannot be assessed 
• T0: no evidence of primary tumour
• T1: tumour ≤2 cm in greatest dimension limited to the thyroid
  • T1a: tumour ≤1 cm, limited to the thyroid
  • T1b: tumour >1 cm but ≤2 cm in greatest dimension, limited to the thyroid
• T2: tumour >2 cm but ≤4 cm in greatest dimension, limited to the thyroid
• T3: tumour >4 cm in greatest dimension limited to the thyroid or any tumour with minimal extrathyroid extension (e.g. extension to sternothyroid muscle or perithyroid soft tissues)

• T4: advanced disease
  • T4a: moderately advanced disease - tumour of any size extending beyond the thyroid capsule to invade subcutaneous soft tissues, larynx, trachea, oesophagus, or recurrent laryngeal nerve
  • T4b: very advanced disease - tumour invades prevertebral fascia or encases carotid artery or mediastinal vessels
  • ​cT4a: intrathyroidal anaplastic carcinoma
  • cT4b: anaplastic carcinoma with gross extrathyroid extension

N: Nodes

• Nx: regional lymph nodes cannot be assessed
• N0: no regional lymph node metastasis
• N1: regional lymph node metastasis
  • N1a: metastases to level VI (pretracheal, paratracheal, and prelaryngeal/Delphian lymph nodes)
  • N1b: metastases to unilateral, bilateral, or contralateral cervical (levels I, II, III, IV, or V) or retropharyngeal or superior mediastinal lymph nodes (level VII)

M: Metastases

• Mx: distant metastases cannot be assessed
• M0: no distant metastasis
• M1: distant metastasis