The eighth edition of the American Joint Committee on Cancer/tumor node metastasis staging system for differentiated thyroid cancer was a better predictor of overall and disease-specific survival than the seventh edition of the staging system regardless of cancer subtype, according to data published in Thyroid.
“This study shows that in a European population of patients with differentiated thyroid cancer harboring a large subset of follicular thyroid cancer patients, applying the AJCC/TNM eighth edition leads to reclassification of 36% of the patients into a lower stage,” Evert F.S. van Velsen, MD, MSc, a PhD student and internist in training at the Academic Center for Thyroid Diseases in the department of internal medicine at Erasmus Medical Center in Rotterdam, the Netherlands, and colleagues wrote. “Furthermore, using this eighth edition, there is no significant difference between papillary thyroid cancer and follicular thyroid cancer anymore regarding survival rates per stage, implying that AJCC/TNM stage is a good predictor for both differentiated thyroid cancer subtypes.”
The researchers evaluated retrospective data from 792 patients (79% with papillary thyroid cancer and 21% with follicular thyroid cancer) who were diagnosed and/or treated at the Erasmus Medical Center in Rotterdam from 2002 to April 2016. Researchers categorized patients according to the seventh edition of the American Joint Committee on Cancer/tumor node metastasis (AJCC/TNM) staging system and then reclassified them using the eighth edition, which was introduced in clinical practice in January.
After a median follow-up of 86 months, 106 patients (13%) had died, 54% from differentiated thyroid cancer. Patients with follicular thyroid cancer were older (P < .001) and had a higher mortality rate (P < .001).
Researchers classified disease stage using both the seventh and eighth editions of the staging systems. Based on the seventh edition, 431 patients (54%) were classified as stage I, 82 (10%) as stage II, 96 (12%) as stage III and 183 (23%) as stage IV. Based on the eighth edition, 282 patients (36%) — 49% with follicular thyroid cancer and 32% with papillary thyroid cancer — were reclassified into a lower stage. The number of patients diagnosed as stage I increased from 431 with the seventh edition to 575 with the eighth edition; similarly, the number of patients diagnosed as stage II increased from 82 to 129. The numbers of patients diagnosed with stage III and stage IV disease decreased from 96 to 30 and 183 to 58, respectively. Researchers found similar patterns when they separately evaluated patients with papillary and follicular thyroid cancer.
To further analyze the reclassification patterns, the researchers classified patients using the eighth edition classification system with the seventh edition’s age cutoff. They found that 271 patients (34%) were still reclassified into a lower stage, but fewer were reclassified to stage I and more were reclassified into stages II and III.
Regardless of stage at diagnosis, patients with papillary thyroid cancer had higher 10-year overall and disease-specific survival compared with patients with follicular thyroid cancer (P < .001) using both editions of the classification system. Stage at diagnosis was related to overall and disease-specific survival for differentiated thyroid cancer as well as papillary and follicular thyroid cancer separately using either edition of the classification system (P < .001). However, the eighth edition showed a better distinction between the stages for survival and a worse prognosis for patients with stage II (10-year disease-specific survival = 100% with the seventh edition vs. 85% with the eighth edition), stage III (96% vs. 46%) and stage IV (59% vs. 28%) thyroid cancer. Researchers observed the same pattern when evaluating papillary and follicular thyroid cancer separately.
“The eighth edition performs well regardless if your patient has papillary or follicular thyroid cancer,” van Velsen told Endocrine Today. “This important information can be used in counseling patients upon diagnosis.” – by Tina DiMarcantonio-Brown
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