👉In October 2016, the AJCC (www.cancerstaging.org)
published the eighth edition of the AJCC / TNM cancer staging system, which replaced the seventh edition that had been used by clinicians, cancer registries, and researchers since 2009.
👉On the 1st of January 2018, tumor registries officially began using the eighth edition for tumor staging.
👉Whereas the staging tables for medullary
thyroid cancer and anaplastic thyroid cancer showed
only minimal changes, the rules for the staging of well differentiated thyroid cancer underwent substantial modifications.
👉These included the following:
- An increase of the age cutoff from 45 years to 55 years of age at diagnosis
- Removal of microscopic extrathyroidal extension as a key component of the staging system
- No longer mandating assignment of stage III to older patients with microscopic extrathyroidal extension or lymph node metastases
- Establishment of a new T3b category for tumors of any size that demonstrate gross extrathyroidal extension involving only the surrounding strap muscles
👉The AJCC Differentiated Thyroid Cancer Committee
carefully considered the possibility of inclusion of mo-
lecular markers (specifically, BRAFV600E and TERT
promoter mutations) in the AJCC prognostic staging
👉Whereas both of these mutations, particularly when present together, have been shown to be predictors of poor clinical outcomes, they appeared to add only marginal benefit to the traditional anatomic staging factors.
👉Thus, molecular characterization of differentiated thyroid cancers, although providing some prognostic information, were not powerful enough factors to merit upstaging tumors to prognostic stages above those mandated by TNM risk factors.
👉Nonetheless, similar to the approach used in the
ATA risk-stratification system, molecular results can be used to refine further and individualize risk within risk categories or stages.
👉The three critical factors that determine the prognostic stage groups of the eighth edition AJCC / TNM cancer staging system include the age at diagnosis, the presence or absence of distant metastases, and the presence or absence of gross extrathyroidal extension.
👉Rather than the use of the standard TNM staging tables provided in the AJCC / TNM manual, I find it
easier to use the flow diagram used by MSKCC to stage patients rapidly based on the key clinical risk factors (age at diagnosis, distant metastasis, gross extrathyroidal extension, and lymph node metastases).
👉In patients age under 55 years, this figure rapidly classifies patients as either stage I (any T, any N, M0) or stage II (any T, any N, M1).
👉In the older patients (55 years or older), additional factors, such as the presence or absence of distant metastasis, invasion of strap muscles, and extent of gross extrathyroidal extension, are also used to define the prognostic stage groups.
👉In the eighth edition of the AJCC / TNM cancer staging system, it was anticipated that the majority of patients would be classified as stage I or stage II, reflecting the excellent outcomes expected in the majority of thyroid cancer patients.
👉A smaller number of patients, particularly the
older patients with either distant metastases or gross extrathyroidal extension, were anticipated to do worse and are therefore classified as stage III or IV.
👉Multiple publications have demonstrated that the
eighth edition of the AJCC / TNM cancer staging system
moved a substantial number of patients into lower
prognostic stage groups without affecting the overall
survival of those lower-stage groups.
👉The patients who remained in the higher-stage groups had poorer prognoses, as expected.
👉This resulted in a much better separation of the four prognostic stage groups with respect to survival, such that 5- to 10-year disease-specific survival (DSS) was:
- 99% in stage I patients
- 88% to 97% in stage II patients
- 72% to 85% in stage III patients
- 67% to 72% in stage IV patients
👉Unlike previous editions of the AJCC / TNM staging
system in which there was substantial overlap in survival in patients with stage I, II, and III disease, the eighth edition provides meaningful separation among the prognostic stage groups that appear to be clinically relevant.
👉The differences in predicted and published 10-year survival rates are best seen when analyzed
based on age group (age less than 55 years vs age equal or greater than 55 years) as shown below.
👉The predicted 10-year DSS has been validated for all age and stage groups, with only the younger (age less than 55 years) stage II patients appearing to do more poorly than anticipated.
👉The lower-than-anticipated 10-year DSS in the younger patients (age less than 55 years) with stage II disease was the result of the stage migration of patients in the 45- to 55-year age
group from seventh edition AJCC stage IV to eighth
edition AJCC stage II.
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