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Combining AJCC, ATA thyroid cancer classifications provides more patient-specific outlooks

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September 13, 2018

Combining the eighth edition of the American Joint Committee on Cancer staging system and the American Thyroid Association risk classification system can provide more precise estimates of recurrence risk and disease-specific survival for patients with thyroid cancer, according to findings published in Thyroid.

Sana A. Ghaznavi

With the release of the eighth edition of the American Joint Committee on Cancer (AJCC) staging system, thyroid cancers diagnosed at age younger than 55 years, rather than 45 years as in the previous edition, are classified as either stage I or stage II disease. This change creates a potential problem.

“Oftentimes we speak about thyroid cancer in young patients (< 55 years old) being a ‘low-risk’ cancer, meaning that patients with this disease have a good prognosis. Indeed, about 98% of patients in the ‘young’ group fall into the lowest stage, stage I, disease,” Sana A. Ghaznavi, MD, interdisciplinary thyroid cancer fellow at Memorial Sloan Kettering Cancer Center, told Endocrine Today. “While young stage I patients have a 98% 10-year disease-specific survival as a group, there exists a small but significant number of patients within this cohort that have a higher risk of dying from thyroid cancer. It is clinically important to identify and manage these patients differently than patients with low-risk disease.”

Ghaznavi and colleagues examined data from 4,881 adults (73% women) with differentiated thyroid cancer who began treatment between 1980 and 2016 and were included in the Memorial Sloan Kettering Cancer Center tumor registry. Participants older than 55 years were excluded, as were those who had a follow-up time of fewer than 2 years after diagnosis and those with anaplastic or medullary thyroid cancer. The final sample was stratified based on age, with one group made up of those aged 18 to 45 years (n = 3,167; stage I, n = 3,131) and the other aged 45 to 55 years (n = 1,714; stage I, n = 1,666).

Among the cohort, 98% fell into the AJCC stage I category. Of those, 37% were of the ATA’s low-risk designation for recurrence while 55% were of intermediate risk. The remaining 8% were of high risk.

The 122 thyroid cancer-related deaths reported in the data made up 2.5% of the sample, which was roughly half of the total deaths in the group (n = 229). Most disease-associated deaths were linked to progressive distant metastases (89%), and 75% of them occurred in adults aged 40 to 55 years. The bulk of the disease-specific deaths occurred at least 5 years after diagnosis.

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Patients with stage I disease had a median time from diagnosis to disease-specific death of 10 years, whereas those with stage II disease had a median of 6.5 years (P = .003). There were 96 disease-specific deaths in the stage I group (n = 4,797) and 26 in the stage II group (n = 84). Additionally, 68% of stage II patients had a disease-specific survival rate of 10 years vs. 98% of stage I patients (P < .0001).

Using ATA’s guideline, high-risk patients had an 87% disease-specific survival rate of more than 10 years, which was down by more than 10% compared with low-risk (100%) and intermediate-risk (98%) patients (P < .0001). Disease-specific deaths were decreased for ATA low-risk patients (zero deaths; n = 1,799) and intermediate-risk patients (59 deaths; n = 2,692) compared with 63 deaths among the 390 classified as high risk.

R. Michael Tuttle

“I don’t think the outcome was particularly surprising since we know that disease-specific survival gets progressively worse with increasing age at diagnosis,” R. Michael Tuttle, MD, of the department of medicine at Memorial Sloan Kettering Cancer Center, told Endocrine Today. “But it was nice to show how both ATA risk and the AJCC stage could be integrated to provide more individualized estimate of disease-specific survival. In fact, the ATA guidelines recommend using both the ATA risk and AJCC staging for risk stratification and patient management.”

With these results, the researchers recommended six classification groups based on ATA risk, AJCC staging and age: stage I, low risk (100% 10-year disease-specific survival); stage I, intermediate risk (98%); stage I, high risk, < 45 years (95%); stage I, high risk, 45-55 years (89%); stage II, high risk, < 45 years (78%); and stage II, high risk, 45-55 years (61%).

“Greater refinement of risk estimates allows us to individualize the management approach of these patients, sparing low-risk patients from unnecessary treatments like radioiodine therapy, and reserving more aggressive therapies for those at highest risk of death from their disease,” Ghaznavi said. “The bottom-line: Not all thyroid cancer is created equal, even in young patients that typically have a good prognosis. By refining the estimates of disease-specific survival in young patients with thyroid cancer, we can begin to move from a ‘one-size-fits-all’ approach to a personalized approach to their oncologic care.” – by Phil Neuffer

Disclosures: The authors report no relevant financial disclosures.