Thyroid (Differentiated)

Minor extrathyroidal extension was removed from the definition of T3 disease. Minor extrathyroidal extension (identified on microscopy only) does not affect either the T category or group stage in the 8^th edition.
The rationale for this change was based on the fact that the fibrous capsule of the thyroid is often incomplete, so it is difficult to differentiate on microscopy the difference between an invasive process and the absence of a well defined capsule.
T3a now is defined as any primary thyroid tumour >4 cm in dimension that remains limited to the thyroid gland.
T3b is now defined as a primary thyroid tumour of any size with gross extrathyroidal extension (identifiable intraoperatively) to the strap muscles only.

N1a now includes both level VI and level VII (central compartment lymph nodes). Previously level VII was considered N1b disease.
N1b is now defined by lateral neck or retropharyngeal lymph node involvement only.

Previously, staging for well differentiated thyroid cancer varied depending on whether you were < 45 or 45 or older. Now, the cutoff has been changed to 55 years.

T Category	Criteria
T0	No evidence of primary tumour
TX	Primary tumour cannot be assessed
T1	2 cm or smaller and limited to the thyroid.
T1a	1 cm or less and limited to the thyroid.
T1b	> 1 - 2 cm and limited to the thyroid.
T2	>2 - 4 cm and limited to the thyroid.
T3	>4 cm and limited to the thyroid OR any size with gross extrathyroidal extension to the straps only.
T3a	>4 cm and limited to the thyroid
T3b	Primary tumour of any size with gross extrathyroidal extension to the straps only.
T4	Gross extrathyroidal extension beyond the strap muscles.
T4a	Gross extrathyroidal extension to the trachea, esophagus, soft tissues of the neck, larynx, or recurrent laryngeal nerve.
T4b	Gross extrathyroidal extension invading the pre-vertebral fascia, carotid artery encasement, or mediastinal vessels.

Note that vocal fold fixation (involvement of the RLN) puts you in the T4a category for differentiated thyroid carcinoma.
Compare this to laryngeal carcinoma, where vocal fold fixation makes you T3.
Other structures involved in the T4a classification are similar to in the larynx (trachea, esophagus, soft tissues of the neck).

N Category	Criteria
NX	Regional lymph nodes cannot be assessed.
N0	No evidence of locoregional lymph node metastasis.
N0a	One or more cytologically or histologically confirmed benign lymph nodes.
N0b	No radiologic or clinical evidence of lymph node metastasis.
N1	Metastasis to regional nodes.
N1a	Metastasis to level VI or level VII (central compartment lymph nodes)
N1b	Metastasis to lateral neck nodes (I-V) or retropharyngeal lymph nodes.

Level VI: Laterally bounded by the common carotids, superiorly by the hyoid, inferiorly by the sternal notch.
Level VII (upper mediastinal): Laterally bounded by the innominate on the right, the left common carotid on the left, the aortic arch inferiorly, and the sternal notch superiorly.

M Category	Criteria
M0	No distant metastasis
M1	Distant metastasis present

	Any N M0	Any N M1
Any T	I	II

If age at diagnosis is < 55:
- Your group stage is Stage I unless you have distal metastasis, in which case you are considered Stage II.
If age at diagnosis is ≥ 55:
- T3 disease upstages you to at least Stage II.
- N1 disease upstages you to at least Stage II.
- T4a disease upstages you to at least Stage III.
- T4b disease upstages you to at least Stage IVA.
- Distal metastasis (M1) upstages you to Stage IVB.

Stage I→ 98-100%
Stage II→ 85-95%
Stage III→ 60-70%
Stage IV→ <50%
Kaplan-Meier curves based on Memorial Sloan Kettering Cancer Centre data (1810 patients between 1986 and 2005) analyzed using 8th Edition Guidelines: