Medullary thyroid cancer staging refers to TNM staging of medullary thyroid carcinomas. Papillary, follicular, and anaplastic thyroid carcinomas have similar TNM category definitions but different prognostic stage group definitions. The following article reflects the 8^th version published by the American Joint Committee on Cancer, which is used for staging starting January 1, 2018 ^1,2.

Primary tumor (T)

• TX: primary tumor cannot be assessed 

• T0: no evidence of primary tumor

• T1: tumor ≤2 cm in greatest dimension limited to the thyroid

  • T1a: tumor ≤1 cm, limited to the thyroid

  • T1b: tumor >1 cm but ≤2 cm, limited to the thyroid

• T2: tumor >2 cm but ≤4 cm, limited to the thyroid

• T3: tumor >4 cm limited to the thyroid or gross extrathyroidal extension invading only strap muscles

  • T3a: tumor >4 cm, limited to the thyroid

  • T3b: gross extrathyroidal extension invading only strap muscles (sternohyoid, sternothyroid, thyrohyoid, or omohyoid muscles)

• T4: advanced disease with gross extrathyroidal extension beyond the strap muscles

  • T4a: tumor invading subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve

  • T4b: tumor extending toward the spine, invading prevertebral fascia, into nearby blood vessels, or encasing carotid artery or mediastinal vessels

Regional lymph node (N)

• NX: regional lymph nodes cannot be assessed

• N0: no regional lymph node metastasis

  • N0a: one or more lymph nodes confirmed benign by cytology/histology

  • N0b: no radiologic or clinical evidence of regional lymph node metastasis

• N1: regional lymph node metastasis

  • N1a: central lymph node metastases to level VI (pretracheal, paratracheal, and prelaryngeal/Delphian lymph nodes) or level VII (upper mediastinal); can be unilateral or bilateral

  • N1b: lateral neck lymph node metastases (levels I, II, III, IV, or V, or retropharyngeal); can be unilateral, bilateral, or contralateral

Distant metastases (M)

The terms pM0 and MX are not valid TNM categories. The following categories may be used:

• cM0: no evidence of metastases

• cM1: distant metastasis

• pM1: distant metastasis, microscopically confirmed

Stage groups

• stage I

  • T1, N0, M0

• stage II

  • [T2, T3], N0, M0

• stage III

  • [T1, T2, T3], N1a, M0

• stage IVA

  • [T1, T2, T3], N1b, M0

  • T4a, [Any N], M0

• stage IVB

  • T4b, [Any N], M0

• stage IVC

  • [Any T], [Any N], M1

Changes since prior versions

Since the 7^th edition, upper mediastinal lymph nodes were added to the N1a category.